Comparison of Electrical

Standards IEC, BS and US

IEC60364, BS7671, NFPA 70

Introduction

This study seeks to determine the differences and similarities between the BS, IEC and NEC standards with

the purpose of preventing fire and shock hazards. As a result, this study revealed that the misapplication of

these standards results in the destruction of equipment and apparatus. Destruction of equipment, printed

circuit boards and appliances can occur when IEC designed equipment is installed to a system that is based

on the NEC and vice versa. The main reason for this loss is because the installer or troubleshooter did not

make provisions for the differences of the standards and power source design. This study revealed that

improper wiring methods, overcurrent protection, and grounding/bonding techniques occur when the

installer does not recognize the difference in the standards. This results in a potential shock, fire hazard, or

reliability issue. In most cases the installer or troubleshooter is not aware of the difference that exists.

Interviews have shown that the installer or troubleshooter did not fully understand the nomenclature used

by the standard that is/was governing the application. The study has also revealed that nomenclature is an

issue. Electron theory is not changed by geography or nomenclature; the principles are the same

worldwide. The applications of the principles however, are different. We found in this study, along with

others, that both the IEC and the NEC were using the same principle and requirement but different

terminology.

Example would be the relationship between the “equipment grounding conductor” (NEC terminology) and

the “protective conductor” (BS & IEC terminology).

The different terminologies are compared in this study.

Understanding the principles of shock and fire protection is imperative for safety and reliability. As the two

standards are compared it becomes apparent that it is impossible to write on paper all scenarios that may

be encountered by the electrical industry. History (100 years) has proven that applying these shock and

fire prevention principles produces reliability of operation and reduces maintenance requirements. We

have advanced considerable since 640 BC when the Greeks discovered the movement of electrons. The

principles of electron flow have not changed but the progress we have made with application and direction

of electron flow has dictated a need for congruent standards. Global electrical needs and commerce

demand a understanding of both standards.

The IEC/BS voltage ranges have the advantage lower current which means the use of smaller wire sizes.

The savings in conductor and raceway sizes can be tremendous. However, the risk of fire and shock

hazards is greater with the higher voltage applications. In retrospect, the Europeans have managed to keep

a good safety record in terms of shock and fire hazards. One of the noted reasons is that Europeans

typically respect and have self-discipline concerning electrical needs.

The NEC is published by the National Fire Protection Association located in Quincy, Massachusetts. The

International Electrotechnical Commission (IEC) is headquartered in Geneva Switzerland. The commission

has a responsibility for creating electrical standards primarily for Europeans. The United States has

participated in the International Electrotechnical Commission for many decades with varying degree of

involvement.

The United States has typically been on the peripheral concerning the European standards until recent

years. The leaders of the IEC have typically been Germans, French, and the British. The South Africans

have made significant contributions in specific areas such as residual current device standards.

The IEC, as would be expected, is heavily based on European and German practices. These practices have

been passed down from previous generations. The IEC manpower toward developing and maintaining

electrical standards is about 10 times that of the United States. Most members on the IEC are very skilled,

competent and multilingual engineers. The IEC standards and the German standards are almost identical.

The procedural difference between the NEC and the IEC is that the NEC is a consensus standard based

upon past shock and fire hazards while the IEC is not a consensus standard. Although shock and fire

hazards are greatly considered by the IEC other considerations are included which may the delayed in the

NEC based on adverse circumstances. The NEC committee members consist of those who are associated in

some form or fashion to electrical industry. The writers of the NEC consist of engineers, electricians,

inspectors and manufactures while the IEC consists primarily of engineers.

Table of Contents Overall Assessment of NEC and IEC ................................................................................................. 6

Electrical Systems ...................................................................................................................... 11

Publication Time Period ............................................................................................................. 11

Adoption (AHJ) ........................................................................................................................... 12

NEC ......................................................................................................................................... 12

IEC .......................................................................................................................................... 12

Equipment Approval .................................................................................................................. 13

Product Requirements ........................................................................................................... 13

Definitions ...................................................................................................................................... 17

Conductors ................................................................................................................................. 17

Branch Circuits ........................................................................................................................... 18

Disconnecting Means ................................................................................................................. 19

Electrical Equipment .................................................................................................................. 20

Exposed Live Parts ..................................................................................................................... 20

Feeders ...................................................................................................................................... 22

Grounding – that trips OCPD When A Ground Faults ................................................................ 23

Equipment Ground ................................................................................................................ 23

Protective Ground ................................................................................................................. 23

Grounding Electrode Conductor – Earth Ground ...................................................................... 24

Guarding of Electrical Equipment .............................................................................................. 24

Overcurrent Protection.............................................................................................................. 25

Short Circuit Protection ............................................................................................................. 25

Overload .................................................................................................................................... 27

Premise Wiring System .............................................................................................................. 27

Qualified Person ........................................................................................................................ 28

Service Drop and Service Supply ............................................................................................... 28

Underground Service ................................................................................................................. 29

Utilization Equipment ................................................................................................................ 29

Requirements for Electrical Installations ....................................................................................... 30

Examination of Equipment ........................................................................................................ 30

Short Circuit Coordination ......................................................................................................... 31

Workmanship............................................................................................................................. 31

Identification Equipment ........................................................................................................... 31

Grounding - Types of Earthing ................................................................................................... 33

Identification of Grounding Means ........................................................................................... 33

Color Code Comparison ............................................................................................................. 36

Identification of Terminals ......................................................................................................... 38

Reverse Polarity ......................................................................................................................... 39

Receptacles Comparison to Sockets .......................................................................................... 39

Ground Fault Circuit Interrupter ................................................................................................ 41

Residual Circuit Device............................................................................................................... 41

Function of a RCD and GF Relay ................................................................................................ 43

Branch Circuits Requirements ................................................................................................... 45

Comparison of Conductor Ampacities ....................................................................................... 46

Conductor Sizing ........................................................................................................................ 48

Overcurrent Protection and Conductor Sizing .......................................................................... 48

Grounding and Bonding Language ............................................................................................ 53

Grounding Technique Based on Power Source ......................................................................... 55

Grounding Central Diesel Power Plants ..................................................................................... 55

Wiring Methods ............................................................................................................................. 58

Protection From Physical Damage ............................................................................................. 58

Voltage Drop Calculations ........................................................................................................ 59

Wet Areas .................................................................................................................................. 60

Temporary Wiring ...................................................................................................................... 61

Cable Trays ................................................................................................................................. 61

Flexible Cords and Cables .......................................................................................................... 63

Motors, Generators and Transformers .......................................................................................... 64

Types of IEC Transformer Systems ........................................................................................ 64

IT network .............................................................................................................................. 65

TT Network ............................................................................................................................ 65

TN networks ........................................................................................................................... 67

TN- C.: ........................................................................................................................................ 67

Hazardous Locations ...................................................................................................................... 68

Appendix 1 ..................................................................................................................................... 84

Overall Assessment of NEC,BS, and IEC

OVERALL ASSESSMENT

• National Electrical Code, NFPA 70

– 100 years old.

– written in mandatory language

– designers, engineers, installers, and enforcement

– close relationship with and reliance on provisions in product standards

The National Electrical Code, NFPA 70

General—The National Electrical Code has been in existence for over 100 years. The NEC is designed to be an

enforcement tool and is written in mandatory and non-mandatory language. The code is suitable for use by AHJ’s

such as inspection services, engineers, maintenance and construction. It is designed to be used in all of the local

industrial, commercial, and residential applications. This standard is to serve as guidance to the authority having

jurisdiction. The primary purpose of the NEC is to provide guidance to prevent shock and fire hazards. Although it

may be used often as a design criterion, it was never intended to be a design manual.

The NEC has been adopted and used in various governing bodies of the United States and in a number of other

countries. It has been translated into several languages including Japanese, Korean, and Spanish. While the NEC

was never intended as performances guide the natural results of preventing shock and fire hazards strengthens

performance and quality assurance. Code rules are generally based on past shock or fire hazards. Construction and

performance of products, equipment, wiring methods, and past practice are taken into consideration when code

rules are determined.

Electrical products must be evaluated and certified not only for risks to life and property, but also for potential

conformity to the installation and use provisions of the NEC. The NEC is revised every three years. Product safety

standards must be reviewed and revised when necessary to maintain continued compatibility. The NEC covers

electrical installations from the service point to the outlets and it includes some requirements for utilization

equipment.

Relationship with Product Standards— the code typically gives the authority having jurisdiction (AHJ) guidance to

determine product reliability and safety. When the AHJ does not have the means to properly test or evaluate

products for safety or reliability they may rely on third-party certification. Third-party certification must be

accomplished by a nationally recognized testing (NTRL). Third-party certification is not mandatory but serves as

guidance to the authority having jurisdiction. Most AHJ rely heavily on internal wiring systems of machines and

equipment to be tested by third-party for certification

Organization, Layout, and Content—the Code consists of an introduction and nine chapters. Chapters 1 through 8

contain articles. Administration is article 80. Introduction is article 90. Chapter 9 contains tables. Appendix is

considered to be advisory along with fine print notes and informational notes. Text is in sections, the numbers for

which include the article designation, e.g. section 110-3. Chapters 1 through 4 of the Code apply generally;

Chapters 5, 6, and 7 apply to special occupancies, special equipment, or other special conditions. These latter

chapters supplement or modify the general rules. Chapters 1 through 4 apply, except as amended by Chapters 5,

6, and 7 for the particular conditions. Chapter 8 covers communications systems and is independent of the other

chapters, except where they are specifically referenced therein.

The provisions of the NEC cover specific requirements for installation, use, and maintenance of electrical systems

in various types of premises, other than those under the exclusive control of electric or communications utilities,

and as stated in Section 90-2(b) of the NEC. The rules also address certain features of utilization (current-using)

equipment. This ensures that proper overcurrent protection and other safety features are provided on the

equipment. The equipment must be suitable for the circuit to which it is connected. Likewise, the circuit must be

capable of supplying the particular connected load(s) without risks to life and property.

OVERALL ASSESSMENT

• International Electrotechnical Commission -IEC 60364

• intended to serve as a basis for development of national requirements

• 1969 – Europe fire and life safety principles

• British Standard BS 7671

• fundamental principles

International Electrotechnical Commission - IEC 60364

General—The standard, Electrical Installations of Buildings, IEC 60364, was developed by the International

Electrotechnical Commission with headquarters in Geneva, Switzerland. This standard was developed around the

same time the national code was developed. European countries are in close proximity to each which made the

need for a universal standard that could be adopted by all countries. In 1969, a concerted effort was made to

harmonize a national wiring method and practice for use by European countries. This effort failed because the

agreement on the rules, methods and practice cannot be agreed. However, it was agreed that a standard to

determine fire and life safety principles and objectives was feasible. These principles then could serve as the basis

on which national wiring practices could be developed.

Chapter 13 IEC 60364

The note to Chapter 13, which covers fundamental principles, indicates that:

“Where countries not yet having national regulations for electrical installations deem it necessary to establish

legal requirements for this purpose, it is recommended that such requirements be limited to fundamental

principles which are not subject to frequent modification on account of technical development. The contents of

Chapter 13 may be used as a basis for such legislation.”

British Standard BS 7671

British Standard BS 7671 – the British standard is based on IEC 60364, "Requirements for electrical installations" in

the United Kingdom for low voltage electrical installations. It is also used as a national standard by Mauritius, St

Lucia, Saint Vincent and the Grenadines, Sierra Leone, Sri Lanka, Trinidad and Tobago, and Uganda, and several

other countries base their wiring regulations on BS 7671. The IET (formerly IEE) has published wiring regulations in

the United Kingdom since 1882. Since their 15th edition (1981), these regulations have closely followed the

corresponding international standard IEC 60364. In 1992, the IEE Wiring Regulations became British Standard BS

7671 and they are now treated similar to other British Standards. They are maintained by the Joint IET/BSI

Technical Committee JPEL/64, the UK National Committee for Wiring Regulations. Although the IET and BSI are

non-governmental organizations and the Wiring Regulations are non-statutory, they are referenced in several UK

statutory instruments.

It is the Technical Committees that, formally, approve a British Standard, which is then presented to the Secretary

of the supervisory Sector Board for endorsement of the fact that the Technical Committee has indeed completed a

task for which it was constituted.

In the United Kingdom wiring installations are regulated by the Institution of Engineering and Technology

Requirements for Electrical Installations: IEE Wiring Regulations, BS 7671: 2008, which are harmonized with IEC

60364. The previous edition (16th) was replaced by the current 17th Edition in January 2008. The 17th edition

includes new sections for micro-generation and solar photovoltaic systems. The first edition was published in 1882.

The BSI publishes numerous titles concerning acceptable standards of design/safety/quality etc. in various fields.

BS 7671 : 2001 (AMD No 2 : 2004) concerns the safety of electrical wiring in buildings (dwellings, commercial,

industrial or otherwise).

IEC and NEC Base

The electrical safety principles cover the need for protection against shock and fire hazards that may occur due to

the use of electricity. Unlike the NEC which is consensus-based. The IEC 60364 is performance-based and is not

intended to be used as a guide for development of national wiring rules.

Organization, Layout, and Content—IEC 60364 is an assembly of 38 separate documents and 10 amendments of

various publication dates. A number of provisions in the documents are incomplete, i.e. they are indicated as

being under consideration. Some of the documents have not been revised since they were issued, as early as

1977.

The IEC 60364 documents cover electrical installations from the service entrance, but stop at the outlets for

current-using equipment. Installations in hazardous locations (explosive atmospheres) are covered in separate IEC

60079 documents. Also, IEC 60364 limits its scope to installations of circuits up to 1000 V, whereas the NEC does

not contain a specific voltage limitation for premises installations. This lack of rules for higher voltages could be a

serious consideration for high-rise building installations.

The fundamental principles contained in Chapter 13 of Part 1 encompass protection for safety: electric shock,

thermal effects, overcurrent, fault currents, and overvoltage; as well as design, selection of electrical equipment,

and erection and initial verification of electrical installations. These basic principles cover known hazards.

Knowledge of the involved hazards and statements for the need of protection against such hazards may not be

sufficient for guarding persons and property without more specific rules on how the protection is to be

accomplished. Other parts of IEC 60364 deal with conditions which may introduce hazards and measures of

protection to be provided.

The numbering system and plan of IEC 60364 are indicated in Annex A to Part 1 of IEC 60364. The numbering

system and updated plan are contained in Annex A-2 of this report. In general, it can be stated that IEC 60364

documents are organized by function. Part 1 contains the scope, object, and fundamental principles. Part 2

contains definitions. Part 3 deals with assessment of general characteristics, such as purposes, supplies, and

structure, classification of external influences, compatibility, maintainability, and safety services. Part 4 addresses

protection for safety. The hazards that are being addressed are electric shock (direct and indirect contact),

thermal effects, overcurrent for conductors and cables, overvoltage, undervoltage, isolation, and switching,

application of protective measures for safety, and choices of protective measures as function of external

influences. Part 5 deals with selection and erection of electrical equipment. It contains common rules, addresses

wiring systems, switchgear, and control gear, earthing arrangements and protective conductors, other equipment,

and safety services. Part 6 covers verification, and Part 7 addresses requirements for special installations or

locations, such as bathrooms, swimming pools, sauna heaters, construction sites, agricultural and horticultural

premises, restrictive conducting locations, earthing requirements for installation of data processing equipment,

electrical installations in caravan parks and caravans, electrical installations in marinas and pleasure craft, medical

locations and associated areas, and electrical installations in exhibitions, shows, stands, and fun fairs.

Example—The difficulty in using the IEC 60364 documents for direct application to an installation can be best

illustrated by example. The statements covering overcurrent protection, permitted type and location of

disconnect means, and other rules concerning installation of appliances, are located throughout the documents

and may be subject to choice and interpretation. For instance, on overcurrent protection, the section on

Protection for Safety has Clause 131.4 covering protection against overcurrent. Section 132 on Design has Clause

132.8 on protective equipment, wherein the characteristics of protective equipment shall be determined with

respect to their function for which the equipment provides protection. Among the effects against which

protection needs to be provided are overcurrent (overload, short-circuit) and earth-fault current. Then, Part 4,

which covers Protection for Safety, has Chapter 43, Protection against Overcurrent. This chapter includes general

statements on the nature of protective devices; protection against overload current, protection against short-

circuits current, and coordination of overload and short-circuit protection. The chapter was issued in 1977, but

contains Amendment No. 1, which deletes references to some outdated fuse types. Protection requirements are

expressed in formulas and deal mainly with protection of conductors. Since the IEC 60364 rules stop at the socket

outlet, overcurrent protection for current-using equipment is not addressed. Typically, electrical equipment is

designed for connection to circuits provided with a specific rating(s) and type(s) of overcurrent device. Lack of

code rules on safety features for electrical equipment could result in inappropriate or hazardous installations. In

addition to the foregoing there is Section 473 on Measures of Protection against Overcurrent. Certain aspects of

overcurrent protection are treated in a number of separate sections.

In a similar manner, Chapter 46 covers Isolation and Switching, while Section 537 covers Devices for Isolation and

Switching. Rules which cover one safety feature are located in different parts of the documents.

Electrical Systems

• North America and Others 120Volts

• European countries and Others 240V

Electrical Systems The NEC specifically has different rules for below 600volts and above 600volts. The nominal voltage system’s are

different when comparing the North American electrical system’s and the European in a system’s. This difference

dictates the type of safety rules that should be applied to different systems.

The North American systems along with other countries typically have a single phase voltage of 120 V, (between

conductors and to ground). Although there are exceptions to the rule. The European countries and some other

parts of the world typically use 240 V, ac, (between conductors and to ground) as the norm. When comparing the

two systems we see that the North American systems typically consist of wye and delta transformer winding

configurations with variations. The European system consists of TT and TN systems with variations. The type

system used as source of energy determines the proper over current protection, wiring methods, grounding, and

bonding techniques required. This will be discussed later in this book, in detail. Countries with TT, TNC, TNS, and

TNCS systems may adopt Chapter 13 on fundamental principles as the guiding principles and adopt the NEC as the

national installation and wiring rules, or they could use IEC 60364 as a basis for development of their national

rules.

In areas of the world where TT premises wiring systems exist, the IEC 60364 documents may be more suitable for

promulgating national wiring rules. The NEC specifically prohibits TT supply systems. The IEC 60364 documents

contain the requirements for the additional safety features, which are necessary for TT supply systems.

Publication Time Period IEC - Approximately two months after final voting period

NEC - Approximately three months after issuance of the new edition by the NFPA Standards Council.

COST –

IEC 60364 single copy: $1900.00 U.S

IEC 60079 - $1784.00 U.S..

NEC 2011- $125.00

Adoption (AHJ)

NEC

1. Adoption by Reference: Public authorities and others are urged to reference this document in laws, ordinances,

regulations, administrative orders, or similar instruments. Any deletions, additions, and changes desired by the

adopting authority must be noted separately. Those using this method are requested to notify the NFPA

(Attention: Secretary, Standards Council) in writing of such use. The term “adoption by reference” means the

citing of title and publishing information only.

IEC

2. Adoption by Transcription: Public authorities with lawmaking or rulemaking powers only, upon written notice to

the NFPA (Attention: Secretary, Standards Council), will be granted a royalty-free license to print and republish this

document in whole or in part, with changes and additions, if any, noted separately, in laws, ordinances,

regulations, administrative orders, or similar instruments having the force of law, provided that: (states conditions

for license).

Some states, counties, cities or other municipalities adopt the NEC with or without deviations by one of the above

methods. Some entities in the U.S. develop their own electrical installation codes.

NOTE: IEC 60364-1, Chapter 13, Fundamental Principles

NOTE: Where countries not yet having national regulations for electrical installations deem it necessary to

establish legal requirements for this purpose, it is recommended that such requirements be limited to

fundamental principles which are not subject to frequent modification on account of technical development. The

contents of Chapter 13 may be used as a basis for such legislation.

Equipment Approval

Equipment Approval

NEC

• NEC - The conductors and equipment required or permitted by the Code shall be acceptable only if approved (110-2). Suitability of equipment may be evidenced by listing or labeling by a qualified electrical testing organization.

IEC

• IEC - “Every item of equipment shall comply with such IEC Standards as are appropriate and, in addition, with any applicable standards of the ISO” (511.1) by visual inspection. ISO – International Standards Organization

• BS – 511.1 & 511.2, Appendix I – Comply with relevant standards.

Product Requirements

Unless noted otherwise, all electrical material used shall be tested by a Nationally Recognized Testing Laboratory

(NRTL) such as Underwriters Laboratories (UL), and display the mark of the NRTL. In the event that NRTL-tested

materials are not available, the contractor may then select applicable IEC manufactured, and CE marked material

but the contractor must prove equivalence and must provide the government with a full copy of the relevant

specification(s)/standard(s). If IEC manufactured, CE marked material is chosen, the product shall be provided with

a “Declaration of Conformity”. The “Declaration of Conformity” contains information to allow tracing of the

product, including product identification, manufacturer’s name, address, signature and standards by which the

product is tested. IEC manufactured, CE marked material shall also be independently certified by a “Notified Body”

A “Notified Body” must serve as an independent test lab and perform tests properly that comply with the

applicable standards and directives called for by the applicable standards. These tests shall be recorded in

“Technical Documentation” by the laboratory and submitted for review. Adopted from AED Design Requirements.

NEC, NFPA 70

• Art. 90 IntroductionPurpose

• “The purpose of this Code is the practical safeguarding of persons and property from hazards arising from the use of electricity.” Furthermore, Sec. 90-1(b) indicates that “this Code contains provisions that are considered necessary for safety. Compliance therewith and proper maintenance will result in an installation that is essentially free from hazard but not necessarily efficient, convenient, or adequate for good service or future expansion of electrical use.”

IEC 60364

• Chapter 12 Object

• to provide safety and proper functioning for the use intended

BS 7671• Chapter 12 Object

• to provide safety and proper functioning for the use intended

National Electrical Code, NFPA 70

NEC - Art. 90 Introduction

Purpose

“The purpose of this Code is the practical safeguarding of persons and property from hazards arising from the use

of electricity.” Furthermore, Sec. 90-1(b) indicates that “this Code contains provisions that are considered

necessary for safety. Compliance therewith and proper maintenance will result in an installation that is essentially

free from hazard but not necessarily efficient, convenient, or adequate for good service or future expansion of

electrical use.” These statements correlate with Chapter 12 of IEC 60364.

IEC and BS 7671 - Chapter 12 Object

Clause 131.1 (Ensure safety)

Clause 12.1 indicates that “this standard contains the rules for the design and direction of electrical installations so

as to provide safety and proper functioning for the use intended.” The rules are expressed in generalities, i.e.

certain means of protection are required to be provided but the methods by which to accomplish the level of

protection specified are not indicated. From Clause 12.1, it is also evident that the object of IEC 60364 is to

provide safety and proper functioning for the use intended. If functioning is intended to include other than safety

functions, such aspects are considered to be outside the scope of the NEC.

NEC - 90-2 Scope

The installations included or excluded from the scope of each of the two documents are similar.

IEC - Chapter 11 Scope

NEC - 90-3 Code Arrangement

In addition, by use of the index and the specific requirements that, in most cases, are located in one particular part

of the Code, the safety aspects of an installation can be readily assessed.

IEC - There is no index to the IEC 60364 documents.

NEC - 90-4 Enforcement

Since the Code has the capability of being used as a legal document, issues relating to enforcement are important.

These are covered in Sec. 90-4.

Not covered

IEC - Aside from Chapter 6 on Verification, IEC 60364 does not address enforcement issues.

NEC - 90-5 Mandatory Rules and Explanatory Material

Mandatory rules, permissive rules, and explanatory material all are clearly defined. In addition, suitability for

adoption as a legal document precludes recommendatory statements.

IEC - Covered in ISO/IEC Directives, Part 3,

Clause 6.5.1, 6.6.1, and Annex E.

NEC - 90-6 Formal Interpretation

The authority having jurisdiction for enforcement of the Code has the responsibility for making interpretations of

the rules; however, there is a mechanism for obtaining formal interpretations by which clarification on the Code

text, not particular installations, can be obtained.

IEC - Not covered

Formal interpretation procedures are not in place.

NEC - 90-7 Examination of Equipment for Safety

In effect, these provisions relieve the inspection authority from delving into internal wiring of appliances and

equipment, and rely for safe operation on equipment that has been certified by a qualified electrical testing

laboratory as meeting appropriate identified standards.

IEC - Part 6 Verification

Compliance with the safety requirements of the relevant equipment standards is to be made by visual inspection

on permanently wired electrical equipment.

NEC - 90-8 Wiring Planning

IEC - Sec. 132 Design

NEC - 90-9 Metric Units of Measurement

IEC - Not covered; inherently metric

Definition

Definitions

NEC

• NEC -Art. 100 Definitions

• Contains only those definitions essential to proper application of the Code

IEC

• IEC - Part 2 Definitions

• Chapter 21 Guide to general

terms.

• Status: Purely informative in nature. Contains informative notes only for some terms in IEC 60050 (826).

BS

• Guide to general terms.

• Part 2

Definitions NEC -Art. 100 Definitions

Contains only those definitions essential to proper application of the Code.

This analysis includes the definitions for which a corollary can be made to an IEC 60050 definition and those

needed for clearer understanding of the U.S. Safety System.

IEC - Part 2 Definitions

Chapter 21 Guide to general terms.

Status: Purely informative in nature. Contains informative notes only for some terms in IEC 60050 (826).

Inside the covers of IEC publications is a note on terminology referring readers to IEC 60050, International

Electrotechnical Vocabulary. The following definitions are from IEC 60050. The definitions are preceded by the IEC

60050 Part designation in parentheses. Brackets contain the title of the Part (for other than Part 826: Electrical

Installations of Buildings).

Conductors

Conductor Carrying Current

NEC

• Article 100

• Ampacity: The current in amperes that a conductor can carry continuously under the conditions of use without exceeding its temperature rating.

IEC• (826) Current-carrying

capacity – Conductor Continuous

• The maximum current which can be carried continuously by a conductor under specified conditions without its steady state temperature exceeding a specified value.

BS• Part 2 – definition• Same as IEC

Branch Circuits

Branch CircuitNEC

• Article 100 - Branch Circuit: The circuit conductors between the final overcurrent device protecting the circuit and the outlet(s).

IEC• 826) Final circuit (of

buildings): A circuit connected directly to current-using equipment or to socket outlets.

Branch orFinal Circuit

Branch orFinal Circuit

BS• Part 2• 314• 433.1.5• 543.7.2

Disconnecting Means

Disconnect or Isolation SwitchNEC - Article 100

• - Disconnecting Means: A device, or group of devices, or other means by which the conductors of a circuit can be disconnected

from their source of supply.

IEC - 826

• (826) Isolation: A function intended to cut off for reasons of safety the supply from all or a discrete section of the installation by separating the installation or section from every source of electrical energy.

BS– 537.1.4• Isolator Part 2

• Switch Main – 537.1.4

Electrical Equipment

Electrical EquipmentNEC – Article 100

• Equipment: A general term including material, fittings, devices, appliances, fixtures, apparatus, and the like used as a part of, or in connection with, an electrical installation.

IEC - 826

• Electrical equipment: Any item used for such purposes as generation, conversion, transmission, distribution or utilization of electrical energy, such as machines, transformers, apparatus, measuring instruments, protective devices, equipment for wiring systems, appliances.

BS – Part 2• Same as IEC

Exposed Live Parts NEC - Exposed (as applied to live parts): Capable of being inadvertently touched or approached nearer than a safe

distance by a person. It is applied to parts not suitably guarded, isolated, or insulated. (See “Accessible” and

“Concealed”)

IEC - (826) Direct contact: Contact of persons or livestock with live parts.

NEC – Article 100 - Live Parts

Electric conductors, buses, terminals, or components that are uninsulated or exposed and a shock hazard exists.

IEC - (826) Live part

• A conductor or conductive part intended to be energized in normal use, including a neutral conductor, but, by convention, not a PEN conductor.

• Note: This term does not necessarily imply a risk of electric shock.

Feeders Art. 215 Feeders

NEC – Article 215 Feeder Circuits extend from service equipment to one or more distribution panelboards

IEC - No set definition

• 314.2 Separate distribution circuits where separate control is needed

• Judgment needs to be exercised in providing separate distribution circuits and those parts of the circuits where separate control is needed.

NEC - Art. 215 Feeders

Feeder: All circuit conductors between the service equipment or the source of a separately derived system and

the final branch-circuit overcurrent device.

Feeders typically extend from service equipment of the premises to one or more distribution panelboards. These

panelboards in turn supply branch circuits. The rules address minimum rating and size, ampacity relative to

service-entrance conductors, overcurrent protection, use of common neutral conductors, need for diagrams, and

various other aspects in regard to auto transformers and tapping circuits from a feeder. A ground-fault circuit

interrupter protection can be used on a feeder to protect all of the branch circuits emanating from the supplied

distribution panelboard. Also, each feeder having a disconnect rated 1000 amperes or more and connected in

specified voltage circuits, is required to be provided with ground-fault protection of equipment. The equipment

ground-fault protectors operate at a level below the potential short-circuit current of a circuit and they operate

before extensive equipment damage has taken place.

Distribution circuits—General rules apply

IEC - 314.2 Separate distribution circuits where separate control is needed

IEC - (826) Distribution circuit (of buildings): A circuit supplying a distribution board.

Judgment needs to be exercised in providing separate distribution circuits and those parts of the circuits where

separate control is needed.

Grounding – that trips OCPD When A Ground Faults

Equipment Ground

Protective Ground

Grounding – That Trips OCPD When A Ground Fault OccursIEC(826) Protective conductor (symbol PE):

• The conductor used to connect the noncurrent-carrying metal parts of equipment, raceways, and other enclosures to the system grounded conductor, the grounding electrode conductor, or both, at the service equipment or at the source of a separately derived system.

• A conductor required by some measures for protection against electric shock for electrically connecting any of the following parts:

• exposed conductive parts,

• extraneous conductive parts,

• main earthing terminal,

• earth electrode,

• earthed point of the source, or

• artificial neutral.

NEC – Article 100Grounding Conductor, Equipment

Grounding Electrode Conductor – Earth Ground

NEC - Grounding Electrode Conductor

• The conductor used to connect the grounding electrode to the equipment grounding conductor, to the grounded conductor, or to both, of the circuit at the service equipment or at the source of a separately derived system.

IEC - (826) Earthing conductor

• A protective conductor connecting the main earthing terminal or bar to the earth electrode.

Guarding of Electrical Equipment

NEC – Article 100 Guarded: IEC - 826 Barrier or Obstacle

NEC - Guarded: Covered, shielded, fenced, enclosed, or otherwise protected by means of suitable covers, casings,

barriers, rails, screens, mats, or platforms to remove the likelihood of approach or contact by persons or objects to

a point of danger.

IEC - (826) Barrier: A part providing protection against direct contact from any usual direction of access.

IEC - (826) Obstacle: A part preventing unintentional direct contact, but not preventing direct contact by

deliberate action.

Overcurrent Protection

NEC – Article 100

• Overcurrent: Any current in excess of the rated current of equipment or the ampacity of a conductor. It may result from overload, short circuit, or ground fault.

IEC - 826

• Overcurrent: Any current exceeding the rated value. For conductors, the rated value is the current-carrying capacity.

Short Circuit Protection

NEC – Article 100 & 110.9 Interrupting Rating

IEC - (441) Short circuit breaking capacity:

NEC - Interrupting Rating: The highest current at rated voltage that a device is intended to interrupt under

standard test conditions.

IEC - (441) Short circuit breaking capacity: A breaking capacity for which the prescribed conditions include a short

circuit at the terminals of the switching device .

[Switchgear, control gear, and fuses]

Overload

NEC – Article 100

• Overload: Operation of equipment in excess of normal, full-load rating, or of a conductor in excess of rated ampacity that, when it persists for a sufficient length of time, would cause damage or dangerous overheating.

IEC - 151

• Overload: The excess of actual load over full load.

• Note: The term “overload” should not be used as a synonym for “overcurrent.” [Electrical and Magnetic Devices]

Premise Wiring System

NEC – Article 100• Premises Wiring (System):

That interior and exterior wiring, including power, lighting, control, and signal circuit wiring…….., that extends from the service point of utility conductors or source of a separately derived system to the outlet(s).

IEC - 826

• Wiring system: An assembly made up of a cable or cables or busbarsand the parts which secure and, if necessary, enclose the cable(s) or busbars.

Qualified Person / Skilled Person

NEC – Article 100

• Qualified Person: One familiar with the construction and operation of the equipment and the hazards involved.

IEC 826, Amendment 2

• Skilled person: A person with relevant education and experience to enable him or her to avoid dangers and to prevent risks which electricity may create.

• Instructed person: A person adequately advised or supervised by skilled persons to enable him or her to avoid dangers and to prevent risks which electricity may create.

• Ordinary person: A person who is neither a skilled person nor an instructed person.

Service Drop and Supply Service

NEC – Article 100

• Service Drop: The overhead service conductors from the last pole or other aerial support to and including the splices, if any, connecting to the service-entrance conductors at the building or other structure.

IEC - 601

• (601) Supply service: A branch line from the distribution system to supply a customer’s installation.

• [Generation, transmission, and distribution of electricity—General]

Power Neutral is tied to Ground at pole and ground rod building

Ground Rod

Underground Service

NEC – Article 100

• Service Lateral: underground service service-entrance conductors from transformer (source) to meter, or other enclosure.

IEC - 601

• Supply service: A branch line from the distribution system to supply a customer’s installation.

• Generation, transmission, and distribution of electricity—General]

Utilization Equipment

NEC – Article 100

• Utilization Equipment: Equipment that utilizes electric energy for electronic, electromechanical, chemical, heating, lighting, or similar purposes.

IEC - 826

• Current-using equipment: Equipment intended to convert electrical energy into another form of energy, for example light, heat, motive power.

Requirements for Electrical Installations

NEC Article 110.2

• Approval

• Acceptable to the authority having jurisdiction.

IEC 60364

• IEC 60364 does not address issues relating to acceptance of an installation.

Examination of Equipment

NEC Article 110.3

• 110-3 Examination, Identification, Installation, and Use of Equipment

IEC

• This section is equivalent of Part 3 of IEC 60364, Assessment of General Characteristics and Chapter 61, Initial Verification.

CAUTION

Short Circuit Coordination

NEC – Article 110.9

• 110-9 Interrupting Rating

IEC – 533.2

• 533.2 Selection of devices for protection of wiring systems against overloads

Current - Limiting

434.3.1 Breaking capacity

Covers series combinations of short circuit protective devices. Note recommends obtaining of details on

coordination from equipment manufacturer.

Workmanship

NEC

• 110-12 Mechanical Execution of Work

IEC

• 134.1.1 (Good workmanship and proper materials)

Identification Equipment

110-22 Identification of Disconnecting Means

This section addresses not only identification of disconnecting means, but also indicates that if a series

combination of overcurrent devices is used, use of the system, the system rating, and that identified replacement

components are needed is also covered by the marking requirement. Because of the dynamic conditions during

the interruption process of short-circuit currents, the acceptability of a series combination of the two overcurrent

devices and the host equipment can be determined only by test. Equipment so evaluated is marked with

information indicated above.

Sec. 514 Identification

Covers identification of purpose

of switchgear and control gear;

identification of wiring for

specific reasons; color coding of

neutral and protective

conductors; identification of

protective devices as to circuit,

etc.; and provision of diagrams.

NEC

• 110-22 Identification of Disconnecting Means

IEC

• Sec. 514 Identification of purpose of switchgear and control gear; identification of wiring for specific reasons; color coding of neutral and protective conductors; identification of protective devices as to circuit, etc.; and provision of diagrams.

Mot

Pump Motor # 5

NEC

• 110-22 Identification of Disconnecting Means

IEC

• Sec. 514 Identification of purpose of switchgear and control gear; identification of wiring for specific reasons; color coding of neutral and protective conductors; identification of protective devices as to circuit, etc.; and provision of diagrams.

Mot

Pump Motor # 5

Grounding - Types of Earthing 312.2 Types of system earthing

546.2.2 The PEN conductor shall be insulated to the highest voltage to which it may be subjected to avoid stray

currents.

200-3 Connection to Grounded System

In conjunction with the foregoing section, the

electricity supply system also is required to have a

grounded circuit conductor (N or PEN conductor).

This rules out use of type IT supply systems, except

in a few specialized cases, one of which is in

patient care areas covered in Art. 517.

Identification of Grounding Means United Kingdom

British Standard BS 7671:2001 Amendment No 2:2004 adopted the IEC 60446 colours for fixed wiring in the United

Kingdom, with the extension that grey can also be used for line conductors, such that three colors are available for

three-phase installations. This extension is expected to be adopted across Europe and may even find its way into in

a future revision of

IEC 60446.

Amendment No 2,

2004 of BS

7671:2001,

Requirements for

Electrical

Installations (the 'IEE

Wiring Regulations'),

formally published

on 31 March 2004,

states the new

(harmonized) colors

and includes

guidance for

alterations and

additions to

installations wired in

the old cable colors.

The new (harmonized) color cables may be used on site from 31 March 2004. New installations or alterations to

existing installations may use either new or old colors, but not both, from 31 March 2004 until 31 March 2006.

Only the new colors may be used after 31 March 2006.

NEC

• Article 250-50, 52 Connection to Grounded System

IEC• 312.2 Types of system earthing

A1 & A2 – Exposed Conductive Parts – Motors, Equipment, etc…B1 & B2 - Extraneous Conductive Parts –Metal Water Pipe, Gas, Building Steel, Rebar etc…

B1 B1

A2A1

IEC -Earth ElectrodeNEC – Grounding

Electrode

IEC-Earthing ConductorNEC-Grounding Electrode Conductor

Main Equipotential

Bonding

IEC - Circuit Protective Conductor

IEC -Main Earthing TerminalNEC – Service Equipment Ground Terminal

NEC -Equipment GroundingConductor

NEC

• Article 250-50, 52 Connection to Grounded System

IEC• 312.2 Types of system earthing

A1 & A2 – Exposed Conductive Parts – Motors, Equipment, etc…B1 & B2 - Extraneous Conductive Parts –Metal Water Pipe, Gas, Building Steel, Rebar etc…

B1 B1

A2A1

IEC -Earth ElectrodeNEC – Grounding

Electrode

IEC-Earthing ConductorNEC-Grounding Electrode Conductor

Main Equipotential

Bonding

IEC - Circuit Protective Conductor

IEC -Main Earthing TerminalNEC – Service Equipment Ground Terminal

NEC -Equipment GroundingConductor

NEC• 200-6 Means of Identifying Grounded

Conductors

• 200-7 Use of White or Gray Color

• 250.119 Equipment Ground

IEC

• 514.3 Identification of neutral and protective conductors

• Per IEC 60446:

• Neutral: Light blue.

• Protective: Green with yellow stripe. Acknowledges U.S. color coding for grounded and equipment grounding conductors.

NEC• 200-6 Means of Identifying Grounded

Conductors

• 200-7 Use of White or Gray Color

• 250.119 Equipment Ground

IEC

• 514.3 Identification of neutral and protective conductors

• Per IEC 60446:

• Neutral: Light blue.

• Protective: Green with yellow stripe. Acknowledges U.S. color coding for grounded and equipment grounding conductors.

The following is history of how the color code, IEC standards, has changed. This will not be covered in class but is

for informational purposes only.

Q1. What are the changes that are proposed for the color identification of conductors?

For the fixed wiring of an installation, it is proposed to replace the traditional colors of red and black for the phase

and neutral conductors of single-phase circuits with brown for the phase conductor and blue for the neutral

conductor. The green-and-yellow bi-color identification of protective conductors will continue unchanged. The

proposed color identification will be familiar, having been used in appliance flexible cables and cords in the United

Kingdom for the past 28 + years.

The proposed colors for the conductors of three-phase circuits are brown, black and grey with a blue neutral

conductor, in place of the traditional red, yellow and blue with a black neutral. Again, the bi-color green-and-

yellow marking of protective conductors will remain unchanged.

The proposed change will implement the use of the core colors introduced in the revision of European

Harmonization document HD 308: Identification of cores in cables and flexible cords, and to align with BS EN

60446: 2000 Basic and safety principles for the man-machine interface - identification of conductors by colors or

numerals.

Q2. Why are the changes for conductor color identification necessary?

The United Kingdom agreed some 28 years ago to adopt the color blue for neutral conductors, and has since used

harmonized (brown/blue/green-and-yellow) colors for the identification of the cores of flexible cables and flexible

cords but, at that time, no move was made towards such harmonization for non-flexible cables used for fixed

wiring. Unfortunately, while the United Kingdom was contemplating such change, much of the rest of Europe was

standardizing on blue for neutral, with brown and/or black phases.

When it became evident in 1999 that, within a few years, a new European Standard would require the use of the

color blue (rather than black) for the neutral conductor of fixed wiring throughout Europe, it became necessary for

the United Kingdom to address the cable color issue with some urgency.

The joint BSI/Institution of Engineering and Technology committee now responsible for the technical content of

the Wiring Regulations (BS 7671) established a Working Group to consider the position the United Kingdom should

take with respect to the harmonization of the colors of the conductors of non-flexible cables for fixed wiring.

The Working Group concluded that the United Kingdom had no realistic option but to agree to use the color blue

for the neutral, and brown for the phase conductor of single-phase circuits.

It also concluded that, due to the widespread adoption in the rest of Europe, the United Kingdom would have to

accept black for one of the other phases of a multi-phase circuit. The Working Group also considered that there

was a need to be able to distinguish between the phases of a three-phase circuit and decided to propose the color

grey for one of the phases, because, of the very few remaining pan-European color options, this seemed to have

the fewest disadvantages.

The Working Group’s recommendations subsequently formed the basis of a United Kingdom proposal which was

accepted by the CENELEC countries almost unanimously. Europe now has the opportunity to fully harmonize the

color identification system not only for non-flexible cables for fixed wiring, but also for flexible cables and cords

and distribution cables.

Q3. How were the changes implemented?

The changes were included in Amendment No 2 to BS 7671:2001 Requirements for Electrical Installations. To assist

with the implementation of the new colors for fixed wiring, the amendment included a new appendix to BS 7671

providing advice on marking at the interface between the old and new colors, and general guidance on the

extended range of colors that may be used for line (not neutral or protective) conductors.

Q4. When did the changes come into effect?

BS 7671 permitted the use of the new conductor colors for fixed wiring commencing on site from 1 April 2004.

Continued use of the old colors was permitted until 1 April 2006, after which time only the use of the new colors

was permissible. During the two year transition period, it was permissible to use either the new or old colors, but

not a combination of both in the same installation work.

Q5. To minimize the number of new installations that will have mixed (old and new) colors, was it permissible to

use conductors with the new colors as soon as they become available, perhaps before BS 7671 was amended?

If a designer or other person responsible for specifying an installation decided to use the new cable colors in

advance of the amendment to BS 7671, it was necessary for that person to record on the Electrical Installation

Certificate for that installation a departure from the requirements of BS 7671, confirming that the same degree of

safety has been provided as that afforded by compliance with the Regulations. Regulations 120-02-01 and 511-01-

02 refer.

However, as some of the proposed requirements, including the marking of cables at terminations, were yet to be

agreed, it may have been impracticable for specifiers to provide the required confirmation until such time as all the

installation requirements had been firmly established by publication of the amendment to BS 7671. Use of the new

colors before all the related safety requirements had been established and communicated to the industry might be

considered inadvisable.

Q6. What is the most significant safety issue?

The change in the United Kingdom to adopt blue for neutral conductor and at least one black for a phase

conductor in a multi-phase circuit could, if not properly addressed, introduce the possibility of confusion with the

black neutral conductor and blue phase conductor in existing three-phase distribution circuits.

However, it is generally considered that the risk is a manageable one. It is acknowledged that other European

countries have reportedly made radical changes in their conductor color identification systems without

immoderate safety ramifications. The public in the United Kingdom is already familiar with a blue neutral and

brown phase in the leads of their domestic appliances.

Color Code Comparison

Gray

US AC Power Circuit Wiring Color Codes

UK AC Power Circuit Wiring Color Codes

Function label Color, IEC Old UK color

Protective earth PE green-yellow green-yellow

Neutral N blue black

Line, single phase L brown red

Line, 3-phase L1 brown red

Line, 3-phase L2 black yellow

Line, 3-phase L3 grey blue

Function label Color, common Color, alternative

Protective ground PGbare, green, or

green-yellow green

Neutral N white grey

Line, single phase Lblack or red (2nd

hot)

Line, 3-phase L1 black brown

Line, 3-phase L2 red orange

Line, 3-phase L3 blue yellow

NEC

• 200-9 Means of Identification of Terminals

IEC

• Not addressed

Identification of Terminals

NEC

• 200-10 Identification of Terminals (for grounded circuit conductor)

IEC

• Not addressed

EquipmentGround

Neutral

Hot Leg orPhase Conductor

NeutralConductor

Reverse Polarity

NEC

• 200-11 Polarity of Connections

IEC

• Not addressed

Reverse Polarity

Receptacles Comparison to Sockets

NEC• 210-7(a) through 210-7(e)

Receptacles and Cord Connectors (Grounding Requirements)

IEC

• NONE - 413.1.1.2 Earthing(other than the general provisions for earthing, no other specifications)

NEC - 210-7(f) Noninterchangeable Types (Receptacles) This provision is needed due to the presence of 120 and

240 volt circuits in dwelling units. In other occupancies, circuits of other voltages with socket outlets may be

present. Other than in recreational vehicles and marine craft, extra-low voltage circuits supplying power are

extremely rare. Art. 720 on circuits and equipment operating at less than 50 volts has been left over from earlier

times when some rural

premises were supplied only by

wind power and storage

batteries operating at the low

voltage. Sec. 210-7(f) is

applicable regardless of the

types of voltages present.

IEC - 411.3.4 Plugs and socket

outlets (for FELV systems only)

Considerable detail in

requirements is provided in

Sec. 411 covering protection

against both direct and indirect

contact by extra-low voltage,

SELV, and PELV sources. This

appears to be an indication that

extra-low voltage sources for supplying limited amounts of power are prevalent. Plugs on SELV and PELV circuits

are not prohibited from having the same configuration as 230 volt socket outlets.

NEC - 210-7(f) Noninterchangeable Types (Receptacles)

This provision is needed due to the presence of 120 and 240 volt circuits in dwelling units. In other occupancies,

circuits of other voltages with socket outlets may be present. Other than in recreational vehicles and marine craft,

extra-low voltage circuits supplying power are extremely rare. Art. 720 on circuits and equipment operating at less

than 50 volts has been left over from earlier times when some rural premises were supplied only by wind power

and storage batteries operating at the low voltage. Sec. 210-7(f) is applicable regardless of the types of voltages

present.

IEC - 411.3.4 Plugs and socket outlets (for FELV systems only)

Considerable detail in requirements is provided in Sec. 411 covering protection against both direct and indirect

contact by extra-low voltage, SELV, and PELV sources. This appears to be an indication that extra-low voltage

sources for supplying limited amounts of power are prevalent. Plugs on SELV and PELV circuits are not prohibited

from having the same configuration as 230 volt socket outlets.

NEC

210-7(f) NoninterchangeableTypes (Receptacles)

IEC

413.1.1.2 Earthing (other than the

general provisions for earthing, no

other specifications)

120 Volt duplex Receptacle

240 Volt Receptacle

230 volt socket outlets

NEC

210-7(f) NoninterchangeableTypes (Receptacles)

IEC

413.1.1.2 Earthing (other than the

general provisions for earthing, no

other specifications)

120 Volt duplex Receptacle

240 Volt Receptacle

230 volt socket outlets

Ground Fault Circuit Interrupter

Residual Circuit Device NEC - 210-8 Ground-Fault Circuit-Interrupter Protection for Personnel

Provision of ground-fault circuit-interrupter protection for personnel requirements have resulted in a notable

reduction in electrocutions in the U.S. These devices are required to have a trip setting of 4-6 mA of ground-fault

current. This level of protection ensures that a person being subjected to the shock current has the ability to let go

of the hazardous object. Typically, these devices are installed at locations or circuits for which they are specified.

Thus, they are not subjected to excessive leakage currents which may cause nuisance tripping. Concepts of whole-

house protection have been explored, however, increases in design trip point, which would be necessary, were

considered to be a reduction in the level of safety. Further efforts in whole-house protection methods are not

being actively pursued by use of GFCI type devices.

IEC -412.5 Additional protection

by residual current devices

IEC - 531.2 Residual current

devices

Clause 412.5 specifies that

protection by residual current

devices (RCDs) is to be provided

as an additional protection

method against electric shock.

The primary protection methods

include insulation of live parts,

barriers or enclosures, obstacles,

and placing out of reach.

The rated operating current for

the RCDs is not to exceed 30

mA. In the opinion of the U.S.

National Code Committee, a 30

mA trip rating is too high to prevent serious physiological effects other than ventricular fibrillation. These other

effects include inability to let go, interference with breathing, etc. (according to publication by Biegelmeier,

Skuggevig, and Takahashi, “The Influence of Low-Voltage Network Systems on the Safety of Electrical Energy

Distribution,” © 1995, UL).

For other than horticultural and agricultural buildings, the IEC 60364 documents specify 30 mA maximum RCDs

only as a method of protection against electric shock. For the above two types of premises, 705.422 specifies 0.5 A

RCDs as protection against fire.

Even though IEC 60364 documents specify 30 mA RCDs only for protection against indirect contact, there are

indications that to achieve the disconnecting times in Table 41A of Sec. 413 in an economical manner, RCDs with

ratings up to 300 mA are used in Europe and possibly elsewhere. Typically, these devices supply all or a number of

circuits in premises.

NEC

210-8 Ground-Fault Circuit-Interrupter Protection for Personnel

• 4-6 mA of ground-fault current

IEC

531.2 Residual Current

Devices

• RCDs is not to exceed 30 mA.

NEC

210-8 Ground-Fault Circuit-Interrupter Protection for Personnel

• 4-6 mA of ground-fault current

IEC

531.2 Residual Current

Devices

• RCDs is not to exceed 30 mA.

NOTE: The higher circuit voltage can create higher touch voltages. Together with the permitted variations in

supply system grounding (earthing) rules, a necessity is created to devote more attention to prevention of shock

hazards due to indirect contact (with accessible parts that may become live due to a fault).

One important consideration in development of new national electrical installation requirements, is the type of

existing infrastructure and electrical supply systems. In areas where the general purpose utilization circuits

operate at 120 V, ac, the NEC may be more appropriate. Even if these circuits operate at 240 V and the supply

systems are of TNS or TNCS type, the NEC could be applied with modifications to some parts of the Code, mainly in

Article 210 sections on branch circuit voltages. The Code also accommodates IT and TNC systems. In the event the

existing branch circuit conductors have metric dimensions and the common conductor sizes and overcurrent

device ratings of the IEC standards are employed, some adjustments in the NEC would be necessary, mostly for

unit conversions. However, from the standpoint of uniform application and enforcement, the NEC, with its

comprehensive requirements, would be a more appropriate base document for development of national wiring

rules.

Function of a RCD and GF Relay

RCD

PCB

Describe the operation of a GFCI and a RCD

Branch Circuits Requirements

NEC - 210-11

Branch Circuits Required

Based on load

calculations as specified in Art.

220 and the proliferation of

electrical appliances, specific

requirements for providing

separate branch (final) circuits

was deemed necessary.

IEC - 132.3 Nature of demand

Indicates only the

parameters that need to be

considered in

determining the number and types

of circuits required.

NEC -110-7 Insulation Integrity

The specification that completed wiring installations shall be free from short circuits and grounds faults. The NEC

does not prescribe test methods

or insulation resistance values.

In a compliant installation, insulation

integrity is achieved by use of wiring

materials and equipment that has

been certified to specified and

identified standards and by proper

installation verified by the

acceptance authorities.

IEC - 612.3 Insulation

resistance of the electrical

installation

Test methods, test voltages, and

minimum insulation

resistance values are

prescribed.

NEC

210-11 Branch Circuits Required• Calculations As Specified In Art. 220

IEC

132.3 Nature of demand

• Determining The Number And Types Of Circuits Required

Determine Branch Circuit Requirements NEC

210-11 Branch Circuits Required• Calculations As Specified In Art. 220

IEC

132.3 Nature of demand

• Determining The Number And Types Of Circuits Required

Determine Branch Circuit Requirements

NEC

• 110-7 Insulation Integrity

IEC

• 612.3 Insulation resistance of the electrical installation

• Test Methods

• Test Voltages

• Insulation Resistance Value

NEC

• 110-7 Insulation Integrity

IEC

• 612.3 Insulation resistance of the electrical installation

• Test Methods

• Test Voltages

• Insulation Resistance Value

NEC

210-11 Branch Circuits Required• Calculations As Specified In Art. 220

IEC

132.3 Nature of demand

• Determining The Number And Types Of Circuits Required

Determine Branch Circuit Requirements NEC

210-11 Branch Circuits Required• Calculations As Specified In Art. 220

IEC

132.3 Nature of demand

• Determining The Number And Types Of Circuits Required

Determine Branch Circuit Requirements

Comparison of Conductor Ampacities

COMPARISON OF CONDUCTOR AMPACITIES

NEC - Article 110-6

• Conductor Sizes (in AWG or circular mils)

IEC – Table 52J Metric

• Minimum cross-sectional area of conductors

COMPARISON OF CONDUCTOR AMPACITIES

Fuse

or

Circuit

Breaker

Protection

Size

Copper

Wire

60Terminal

Types - TW, UF

Copper

Wire

75 C Terminal

Types - RHW, THHW, THW, THWN, XHHW, USE, ZW

AWG (mm2) AWG (mm2)

15 14 (2.5mm² ) 14 (2.5mm² )

20 12 (4mm² ) 12 (4mm² )

25 10 ( 6mm²) 10 ( 6mm²)

30 10 ( 6mm²) 10 ( 6mm²)

35 8 (10mm² ) 8 (10mm² )

40 8 (10mm² ) 8 (10mm² )

45 6 (16mm² ) 6 (16mm² )

50 6 (16mm² ) 6 (16mm² )

60 4 (25mm² ) 6 (16mm² )

70 4 (25mm² ) 4 (25mm² )

80 3 (25mm² ) 4 (25mm² )

90 2 (35mm²) 2 (35mm²)

100 2 (35mm² ) 2 (35mm²)

110 2 (35mm² ) 2 (35mm²)

125 1/0 (50mm² ) 1 (50mm² )

150 2/0 (70mm² ) 1/0 (50mm² )

175 3/0 (95mm² ) 2/0 (70mm² )

200 4/0 (120mm² ) 3/0 (95mm² )

225 250 (120mm² ) 4/0 (120mm² )

250 300 (150mm² ) 250 (120mm² )

300 400 (240mm² ) 350 (185mm²)

350 500 (240mm² ) 400 (240mm² )

400 700 (400mm² ) 500 (240mm² )

400 600 (300mm²)

Table 1 - Based on NEC Table 310.16 and IEC 60364-5-52 Table A 52-4

One of the standard conductor temperature ratings is 75°C in the NEC, whereas in Part 5, Sec. 523 of IEC 60364,

the closest standard rating to 75°C is 70°C. If the NEC ampacities were recalculated for a 70°C maximum

temperature, the allowable ampacities would be lower yet.

Conductor Sizing

NEC 210-19 Conductors—Minimum Ampacity and Size

• Conductor Size Is To Be Based On The Noncontinuous Load Plus 125% Of The Continuous Load Connected

IEC - Conductor Size Table 52J based on various applications

Conductor Sizing

NEC- 210-19 Conductors—

Minimum Ampacity and Size

Due to the performance

characteristics of overcurrent

devices used in conjunction with the NEC, the minimum conductor size is to be based on the noncontinuous load

plus 125% of the continuous load connected to the branch circuit. Continuous load is defined as a load that

operates continuously for three hours or more. Typically, such loads are lighting loads, air conditioning loads, and

electric heating loads.

FPN No. 4 provides information on voltage drop, which for other than fire pump motors, is considered a design

consideration, not safety.

The provisions in this section also specify the minimum size of branch circuit conductors which is No. 14 AWG (2.08

mm²). Some exceptions permit tap conductors as small as size No.18 AWG (0.823 mm²).

IEC - Sec. 133 Selection of electrical equipment

133.2 Characteristics

Table 52J indicates minimum size conductors for various applications. For power and lighting circuits, the table

indicates 1.5 mm² copper which is close to size No. 16 AWG, and 2.5 mm² for aluminum conductors. Aluminum

conductors in the smaller sizes (No. 12 and No. 10 AWG) are no longer available in the U.S.

Sec. 525 has a title voltage drop in consumers’ installations. This section is indicated as under consideration.

There is no indication on voltage drop for other than consumers’ installations. Some generic statements are made

in Chapter 45 on protection against undervoltage, leaving the protection needed as a judgment item.

Overcurrent Protection and Conductor Sizing

Overcurrent Protection and Conductor Sizing

1. Non continuous operation: The load is not operating over 3 hours continuous. The breaker size would be based on maximum load. Example: 100 amp maximum load x 100% = 100 amp breaker size.

2. Continuous operation: Defined by the NEC is the maximum load on for 3 hours are more. The breaker would be sized for the maximum load plus 25 percent. Example: 100 amp load x 125% = 125 amp breaker size.

3. Continuous and non continuous mixed loads: The breaker would be sized for not less than 100 % of the non continuous load plus 125 % of the continuous load.

Overcurrent Protection and Conductor Sizing

1. Non continuous operation: The load is not operating over 3 hours continuous. The breaker size would be based on maximum load. Example: 100 amp maximum load x 100% = 100 amp breaker size.

2. Continuous operation: Defined by the NEC is the maximum load on for 3 hours are more. The breaker would be sized for the maximum load plus 25 percent. Example: 100 amp load x 125% = 125 amp breaker size.

3. Continuous and non continuous mixed loads: The breaker would be sized for not less than 100 % of the non continuous load plus 125 % of the continuous load.

AED DESIGN REQUIREMENTS - CABLE AND BREAKERS SIZING

Overcurrent

protection for

conductors and

equipment is

provided to open the

circuit if the current

reaches a value that

will cause an

excessive or

dangerous

temperature in the

conductors or

conductor insulation.

It is very important

that the ampacity of

the breaker properly

protect the

conductors. This

document does not

include instruction for

motor protection (See

National Electrical Code (NEC) Article 430 for motor protection).

• Breakers are normally sized based on the maximum load that will pass through them on a continuous or non

continuous operation (NEC Article 210.20(A)).

1. Non continuous operation: The load is not operating over 3 hours continuous. The breaker size would be based

on maximum load. Example: 100 amp maximum load x 100% = 100 amp breaker size.

2. Continuous operation: Defined by the NEC is the maximum load on for 3 hours are more. The breaker would be

sized for the maximum load plus 25 percent. Example: 100 amp load x 125% = 125 amp breaker size.

3. Continuous and non continuous mixed loads: The breaker would be sized for not less than 100 % of the non

continuous load plus 125 % of the continuous load.

• Conductors shall be sized based on Table 1, and NEC 240.4. The table was created based on a worst case

capacity from NEC Table 310.16 and IEC 60364 Table A.52-4. Table 1 ampacity values are valid for 3 current

carrying-conductors or less in a conduit or raceway, at an ambient temperature of 30°C. If actual conditions differ

from these values, Table 2 (correction for number of conductors) and Table 3 (correction for ambient temperature)

shall be used to adjust the capacity for conductors shown in Table 1.

Adjustment FactorsNEC –Table 310 – 15(B)(16) Adjustment Factors for More Than Three Current-Carrying Conductors in a Raceway or Cable

Number of Current-Carrying

Conductors

Percent of Values in Tables

Table 310.15 2011

edition

4-6 80

7-9 70

10-20 50

21-30 45

31-40 40

41 and above 35

IEC - Table 52-E1 - Correction factors for groups

of more than one circuit or more than one

multicore cable

Number of

Circuits

Table 53-2E1

Number of

Loaded

Single –Core

Conductors

In A Group

Correction

Factors For

Values In

tables 52-C1

to 52-C6

1 3 1.00

2 6 0.80

3 9 0.70

4 12 0.65

5 15 0.60

6 18 0.55

7 21 0.55

8,9,10 24-30 0.50

12, 14 36-42 0.45

16,19,20 48-60 0.40

Adjustment FactorsNEC –Table 310 – 15(B)(16) Adjustment Factors for More Than Three Current-Carrying Conductors in a Raceway or Cable

Number of Current-Carrying

Conductors

Percent of Values in Tables

Table 310.15 2011

edition

4-6 80

7-9 70

10-20 50

21-30 45

31-40 40

41 and above 35

IEC - Table 52-E1 - Correction factors for groups

of more than one circuit or more than one

multicore cable

Number of

Circuits

Table 53-2E1

Number of

Loaded

Single –Core

Conductors

In A Group

Correction

Factors For

Values In

tables 52-C1

to 52-C6

1 3 1.00

2 6 0.80

3 9 0.70

4 12 0.65

5 15 0.60

6 18 0.55

7 21 0.55

8,9,10 24-30 0.50

12, 14 36-42 0.45

16,19,20 48-60 0.40

NEC

Table 310-15(b)(2)(a): Adjustment Factors for More Than Three Current-Carrying Conductors in a Raceway or

Cable

[Applies also to single conductors or multiconductor cables in free air, stacked or bundled more than 24 in. (0.61

m)]

The foregoing adjustment factors apply where all current-carrying conductors carry current continuously. Where

load diversity is involved, such as may be the case in numerous industrial applications, for more than nine

conductors in a raceway or cable, Table B310-11 provides factors with less severe reduction in ampacities than the

values shown above.

Conductor sizes and types have an influence on the amount of current a conductor can carry where the conductor

is installed in close proximity to other current-carrying conductors. For practical reasons the numbers given for the

adjustment factors are not exact. However, they serve well to ensure minimum levels of safety that can be

achieved by design, installation, and verification.

IEC

Table 52-E1: Correction factors for groups of more than one circuit or more than one multicore cable

[Note 6 has been applied to the number of single core cables to facilitate direct comparison]

The foregoing values apply to single-core conductors or cables bunched on a surface or enclosed in conduit or

trunking.

Table 52-E1 is expressed in terms of numbers of circuits and multicore cables. According to Note 6, for groups of

single-core conductors the number of groups of conductors have to be divided either by two or three to arrive at

the number of circuits in the Table. This alternative can result in a difference of five percentage points in some

correction factors.

Table 310.15(B)(2)(a) Ambient Temperature Correction Factors Based on 30° C (86° F)

For ambient temperatures other than 30° C (86° F), multiply the allowable ampacities specified in the ampacities

specified in the ampacity tables by the appropriate correction factor shown.

Correction Factors for Ambient Temperature

NEC Table 310.15(B)(2)(a)IEC - Table 52-D1: Correction factors for ambient air temperatures other than 30C

Ambient PVC InsulatedTemp. (C) 70C Conductors

10 1.2215 1.1720 1.1225 1.06-- --

35 0.9440 0.8745 0.7950 0.7155 0.6160 0.50

Correction Factors for Ambient Temperature

NEC Table 310.15(B)(2)(a)IEC - Table 52-D1: Correction factors for ambient air temperatures other than 30C

Ambient PVC InsulatedTemp. (C) 70C Conductors

10 1.2215 1.1720 1.1225 1.06-- --

35 0.9440 0.8745 0.7950 0.7155 0.6160 0.50

Correction Factors for Ground Temperature

IEC

Ground PVC InsulatedTemp. (C) 70C Conductors

10 1.1015 1.05-- --

25 0.9530 0.8935 0.84

Table 52-D2: Correction factors for ambient ground temperatures other than 20C

NEC - Art. 220 Branch-Circuit, Feeder and Service Calculations

• Example - lighting loads 0.25 and 3.5 VA per square foot depending on application diversity

IEC - 133.2.4 Power equipment is to be selected to be suitable for the load

• Maximum demand and diversity

• No guidance diversity factors and conditions

Art. 220 Branch-Circuit, Feeder and Service Calculations

The NEC contains specific rules for calculating the size of electrical service, feeders, and branch circuits, and how

much load can be safety connected to each. General lighting loads are based on volt-amperes per square foot and

the volt-ampere values vary between 0.25 and 3.5 VA per square foot. There are various demand factors for

multiple loads where all of the loads are not expected to be energized at the same time.

For feeder and service loads, there are optional calculations which are permitted to be used. Farms have a

different load composition, therefore, separate rules are specified for computing farm loads.

133.2.4 Power equipment is to be selected to be suitable for the load

Sec. 311 Maximum demand and diversity

Maximum demand and diversity are two factors that need to be considered in sizing electrical circuits, and the

power equipment is to be selected to be suitable for the load.

No guidance is provided for determining diversity factors and conditions under which they can be applied. Each

country has to determine the minimum safe electrical service that can be provided for premises and how much

load can be applied to each circuit.

Grounding and Bonding Language

Grounding Language

NEC

• Grounding Electrode

• Grounding Electrode Conductor

• Equipment Ground

• Neutral (Grounded Circuit Conductor)

• Bonding

IEC

• Earth

• Conductor to Earth –Protective Earth (PE)

• Protective Conductor

• Neutral

TN−S PE and N are separate conductors that are connected together only near the power source. TN−C A

combined PEN conductor fulfills the functions of both a PE and an N conductor. Rarely used. TN−C−S Part of the

system uses a combined PEN conductor, which is at some point split up into separate PE and N lines. The combined

PEN conductor typically occurs between the substation and the entry point into the building, and separated in the

service head. In the UK, this system is also known as protective multiple earthing (PME), because of the practice of

PEN conductor fulfills the functions of both a PE and an N conductor

• PE – Protective Earth

• N – Neutral

• PME – Protective Multiple Earthing

PEN conductor fulfills the functions of both a PE and an N conductor

• PE – Protective Earth

• N – Neutral

• PME – Protective Multiple Earthing

connecting the combined neutral-and-earth conductor to real earth at many locations, to reduce the risk of broken

neutrals - with a similar system in Australia being designated as multiple earthed neutral (MEN).

Grounding Technique Based on Power Source

Grounding Technique is Based on Power Source

NEC

• Single Phase

• Three Phase Wye Ungrounded

• Three Phase Grounded Wye

• Three Phase Delta Ungrounded

• Three Phase Delta Grounded– Center Tap

– Corner Tap

IEC

• TT System• TN - C System – A Multi-

Grounded Neutral System• TN-S System – 3Phase System

Also Used As Single Phase, 2-Wire and 3-Wire Systems With Ground

• TN-C-S System – Common neutral and protective Conductor. Most Commonly Used because it uses both the C and S configurations in the same facility.

*Grounding

Grounding Central Diesel Power Plants

60Hz systems: Grounding shall be designed and installed accordance with NEC Article 250. Most AED-N projects

have central diesel power plants, and a main distribution panel that feeds all buildings. Each building in these

compounds is considered a “Building Supplied by a Feeder” by NEC 225.30, and is bound by the grounding

requirements of NEC 250.32. NEC 250.32(A) requires a grounding electrode at buildings supplied by a feeder.

50Hz systems: Grounding system shall be TN-S Earthing System, as identified in BS7671. Additional earthing of the

Protective Earth is required for all projects. The PE shall be connected to all available grounding electrodes

available at the building,

including but not limited to:

Building Steel, Concrete

Encased Electrode, and

Ground Rods.

If a transfer switch is

provided ahead of the Main

Distribution Panel, it must be

Service Entrance rated, or a

Service-Rated disconnect

switch with an overcurrent

protection device must be

provided on the Utility

(transformer) side of the

transfer switch.

See NEC 230.83 “Equipment Connected to Supply Side of Service Disconnect.”

* Adopted from AED Electrical Design Requirements

Grounding Central Diesel Power Plants

NEC - 60Hz systems

• Feeder Grounding

• NEC 225.30

• NEC 250.32(A)

IEC - 50Hz systems

• TN-S Earthing System, BS7671

• PE shall be connected to all available grounding electrodes available at the building, including but not limited to: Building Steel, Concrete Encased Electrode, and Ground Rods.

Grounding Central Diesel Power Plants

NEC - 60Hz systems

• Feeder Grounding

• NEC 225.30

• NEC 250.32(A)

IEC - 50Hz systems

• TN-S Earthing System, BS7671

• PE shall be connected to all available grounding electrodes available at the building, including but not limited to: Building Steel, Concrete Encased Electrode, and Ground Rods.

GroundingNEC – Generators 60 Hz

• Separately Derived System

• Article 250.32 , 2011 edition

• Grounding Electrode System

• Article 250.52, 2011 edition

IEC – Generators 50 Hz

• TN-S Earthing System, as identified in BS7671.

• Additional earthing of the Protective Earth is required for all projects.

• The PE shall be connected to all available grounding electrodes available at the building, including but not limited to: Building Steel, Concrete Encased Electrode, and Ground Rods

Wiring Methods

Protection From Physical Damage

Protection From Physical DamageNEC – Article 300-4

• Protection Against Physical Damage

IEC – 522.6,7&8

• 522.6 Impact

• 522.7 Vibration

• 522.8 Other mechanical stresses

NEC

• 300-6 Protection Against Corrosion

• 300-5 Underground Installations

IEC

• 522.5 Presence of corrosive or pollution substances

• Table 52H, Reference numbers: 5, 5A, 21 through 24A, 52, 53, 61, 62, 63

NEC - 300-7 Raceways Exposed to Different Temperatures

IEC - Other than fundamental principles, not covered

Grouping of ConductorsNEC Article 300-20 Induced Currents (grouping of conductors and single conductor entries into ferromagnetic enclosures)

IEC - 521.5 All conductors to be grouped in same enclosure where ferromagnetic enclosures are used

Voltage Drop Calculations The voltage drop of any insulated cable is dependent upon the length of the cable, the current on the cable and

the impedance (ohm) per unit length of the cable based on the type of conduit. Voltage drop on the cable shall be

limited to the following:

- The voltage drop of the secondary service

of 3%. - The voltage drop of a feeder or branch

circuit of 2%.

The combined voltage drop of feeder and

branch circuit shall not exceed 5%. Voltage

Drop Calculations shall be provided in

accordance with the NEC, regardless of where

the cable was manufactured. U.S Formula

(NEC) For three phase: VD = 1.732 x L x R x I /

1000 For single phase: VD = 2 x L x R x I / 1000

VD: The voltage drop (V) L : The length of

conductor (m) R: The impedance value from

NEC Chapter 9, Table 9 (ohm/km) [or Table 1 of Section 2 above] I : The load current (A) The value R is

determined from the National Electrical Code (NEC), Chapter 9, Table 9 column “Effective Z at .85 PF for Uncoated

Copper” using the ohm/km column. See Table 2 below for the NEC table data presented in the USACE Allowable

Capacities of Conductors chart. Below is an example calculation for determining voltage drop. Determine the

voltage drop of a 380V, 3 phase circuit with a current of 100A and a length of 150 m and a conductor size of 50 mm

in steel conduit. This is a secondary service feed. VD = 1.732 x Length x Impedance x Current / 1000. Impedance

is found in Table 1 of Section 2 above: = 1.732 x 150 x 0.52 x 100 /1000 = 13.51 V

Voltage Drop Considerations

NEC

• No mandatory action

• Information note to Article 215.3.Informationnote 2, 3 & 4

IEC

• No mandatory action

Voltage Drop Considerations

NEC

• No mandatory action

• Information note to Article 215.3.Informationnote 2, 3 & 4

IEC

• No mandatory action

Wet Areas 60Hz systems: Provide GFCI protected circuits (either by breaker, or GFCI receptacle) IAW NEC 210.8(B). Locations

requiring GFCI protection include, but are not limited to: bathrooms, kitchens, rooftops, outdoors, and within

1800mm of sink basins. GFCI devices shall have a trip rating of 4-6mA. 50Hz systems: Provide RCD’s where

required by BS7671. RCD’s shall be used in conjunction with overcurrent protection, preferably in the same device

(RCBO). Current using devices shall not be provided within Zone 2.

Receptacles shall not be provided within 3 meters of the boundary of Zone 1.

RCD’s shall have a maximum trip rating of 30mA.

ANSF projects:

Omit general-purpose receptacles from all wet areas, unless shown on site-adapt plans.

U.S./NATO Occupied Facilities:

All circuits feeding latrines/bathrooms/restrooms

shall be protected by either GFCI’s or RCD’s.

These circuits include, but are not limited to:

Receptacles

Lights

Split-pack HVAC units

Exhaust fans

unit heaters

Water heaters

Exhaust fans

Temporary Wiring

Temporary Wiring

1. Art. 590 Temporary Wiring

2. 590-4(d) Receptacles

3. 590-4(f) Lamp Protection

4. 590-4(h) Protection from Accidental Damage

1. Sec. 704 Construction and demolition site installations

2. 704.538 Plugs and socket outlets

3. Not specifically stated

4. 704.521.1.7.3 (Mechanical protection, not run across roads)

Cable Trays

Cable Trays

Art. 392 Cable Trays Chapter 52 Wiring systems; cable ladder; and cable tray

NEC - Art. 392 Cable Trays

This article covers four types of cable trays: ladder type, ventilated trough, ventilated channel, and solid bottom

type. There are different rules for each construction due to their means for dissipation of heat, provision of

physical protection, support for conductors, and other aspects as covered in the article.

Cable trays are a support method for cables and raceways, but they are not to be treated as a raceway system.

The rules in Art. 318 are distinct and different from those for raceway systems covered in other articles of Chapter

3. The open construction, provision of direct ventilation, ability to maintain routing, and separation between

cables or raceways—all of these allow rules that achieve effective levels of safety, different from those for

enclosed raceways.

The rules include the types of cables and raceways that may be placed in a cable tray, construction specifications,

installation as a complete system, accessibility, grounding, installation of cables, allowable cable fill, and ampacity

of cables. These rules vary for single or multiconductor cables and for the type of cable tray construction.

The comprehensive and specific rules provide for uniform application and enforcement to provide equivalent

levels of safety from one installation to the next.

IEC - Chapter 52 Wiring systems; cable ladder; and cable tray

Cable ladders and cable trays are included among all other wiring systems covered in Part 5. Solid bottom,

perforated trays, and ladders are indicated in Table 52H. Other than the fundamental principles on safety and the

correction factors for current-carrying capacity in Tables 52-E4 and -E5, there are no other rules to guide the

installer or verifier. Notes which are not part of the requirements allude to potential problems with certain

installations, such as with more than one layer of conductors and how to treat parallel conductors.

Flexible Cords and Cables

Art. 400 Flexible Cords and Cables

Typically, flexible cords are used in factory- or field-made cord sets, or power supply cords, as pendants, and as

replacement for damaged cords. The larger cables and those for specific uses are covered as well to assure

uniformity in construction and performance. Even though there are product standards that contain detailed

requirements, the Code rules address

general characteristics such as

identification, range of sizes, type, and

thickness of insulation, outer

covering, and use for which the cord or

cable is intended.

Normative references, Chapter 52 on

wiring systems

IEC - 522.7 Vibration

Wiring systems shall be suitable for such

conditions. Also, 522.8.1.8

indicates that flexible wiring systems

shall be installed so that excessive tensile stress to the conductors and connections is avoided.

Since the

Flexible Cords and Cables

NEC

• Art. 400 Flexible Cords and Cables

• Installation

• Size

• Type

• Insulation

• Identification

IEC

• 522.7; 8.1.8 Vibration -flexible wiring systems shall be installed so that excessive tensile stress to the conductors and connections is avoided.

• IEC 60364 rules cover wiring from the service to the socket outlets, power supply cords for current-using equipment or other cords, such as for pendants.

Flexible Cords and Cables

NEC

• Art. 400 Flexible Cords and Cables

• Installation

• Size

• Type

• Insulation

• Identification

IEC

• 522.7; 8.1.8 Vibration -flexible wiring systems shall be installed so that excessive tensile stress to the conductors and connections is avoided.

• IEC 60364 rules cover wiring from the service to the socket outlets, power supply cords for current-using equipment or other cords, such as for pendants.

Motors Generators and Transformers

NEC

• Art. 430 Motors, Motor Circuits, and Controllers

• Art. 445 Generators

• Art. 450 Transformers and Transformer Vaults (Including Secondary Ties)

IEC

• General Reference

• Sec. 551 Low-voltage generating sets

• Types of transformers under the scope of Art. 450 not covered

Motors Generators and Transformers

NEC

• Art. 430 Motors, Motor Circuits, and Controllers

• Art. 445 Generators

• Art. 450 Transformers and Transformer Vaults (Including Secondary Ties)

IEC

• General Reference

• Sec. 551 Low-voltage generating sets

• Types of transformers under the scope of Art. 450 not covered

Motors, Generators and Transformers

Normative references, general rules

Art. 440 Air Conditioning and Refrigerating

Equipment

Note: Also see Annex D of this report for an

example circuit.

Normative references, general rules

Generators

NEC - Art. 445 covers Generator use and installation issues.

IEC - Sec. 551 Low-voltage generating sets

Mutual Inductance principles are the same for both NEC and IEC systems. This includes motors, transformers and

generators. Windings are wound differently thus producing different voltage and frequency outputs. See our book

on transformers, generators and Motors for a more in-depth look.

Transformers and Transformer Vaults (Including Secondary Ties)

Transformer types under the scope of Art. 450and 250, NEC, are not covered in IEC

Comparison of NEC and IEC Transformer Systems

The reason we compare the systems is because how we design and apply grounding, overcurrent

protection, wiring methods along with codes and standards is dependent on the source. The winding

of transformers, generator and motors is the first step to determine how to properly apply codes and

standards. I find many misinterpretations and applications are due to not properly matching the

standard to the power source.

For example: if we apply the principles (standards) of grounding to a grounded wye that we apply to ungrounded

delta we will create objectionable currents that can create shock and fire hazards. If we apply the same standard to

a IEC- TT system to a TN-C System, objectionable currents will flow in directions never intended and result in

potential shock and fire hazards.

Types of IEC Transformer Systems

Comparing the US transformer system to the European system has some differences. The US system is based on a

frequency of 60 Hz, cycles per second; the European system is based on 50 Hz, cycles per second. The major

difference is the utilization of voltage required of each system. The European system are served by three phase, 4

–wire systems with voltage ranges from 380 Y/220 v, 400 Y./230v., and 416 Y/240 v.

The US system voltages are not typically those of the European systems. The nominal voltage systems consist of

480/277Y, 480/ 240 Y, 480/240 d, 208/120 Y., 240/120d, and a variety of single phase and multi-grounded systems.

The higher voltage ranges in the European system have the advantage of lower average which means the use of

smaller wire sizes. The savings in conductor and raceway sizes can be tremendous. However, the risks of fire and

shock hazards are greater with the high-voltage. However, the Europeans have managed to keep a good safety

record in terms of shock and fire hazards. One of the noted reasons is that Europeans typically respect and have

self-discipline concerning electrical needs.

The International Electrotechnical Commission (IEC) is headquartered in Geneva Switzerland. The commission has

a responsibility for creating electrical standards for Europeans. The United States has participated in the

International Electrotechnical Commission for many decades with varying degree of involvement.

The United States has typically been on the peripheral concerning the European standards until recent years.

Leaders of the IEC have typically been Germans, French, and the British. The South Africans have made significant

contributions in specific areas such as residual current device standards.

The IEC, as would be expected, is heavily based on European and German practices. The IEC manpower toward

developing and maintaining electrical standards is about 10 times that of the United States. Most members on the

IEC are very skilled, competent and multilingual engineers. The IEC standards and the German standards are

almost identical.

Again the basic difference between the NEC and the IEC is that the NEC is a consensual standard based upon past

shock are fire hazards while the IEC is not a consensual standard. The NEC committee members consist of those

who are associated in some form or fashion to electrical industry. The NEC committees consist of engineers,

electricians, inspectors and manufactures.

IT network

In an IT network, the distribution system has no connection to earth at all, or it has only a high impedance

connection. In such systems, an insulation monitoring device is used to monitor the impedance. For safety reasons

this network is not accepted under European norms.

TT Network

In a TT earthing system, the protective earth connection of the consumer is provided by a local connection to

earth, independent of any earth connection at the generator.

The big advantage of the

TT earthing system is the

fact that it is clear of high

and low frequency noises

that come through the

neutral wire from various

electrical

equipment

connected to it. This is

why TT has always been

preferable for special

applications like

telecommunication sites that benefit from the interference-free earthing. Also, TT does not have the risk of a

broken neutral.

In locations where power is distributed overhead and TT is used, installation earth conductors are not at risk

should any overhead distribution conductor be fractured by, say, a fallen tree or branch.

In pre-RCD era, the TT earthing system was unattractive for general use because of its worse capability of

accepting high currents in case of a live-to-PE short circuit (in comparison with TN systems). But as residual current

devices mitigate this disadvantage, the TT earthing system becomes attractive for premises where all AC power

circuits are RCD-protected.

The TT system has the ground point to Earth located at the pole or pad mounted transformer. The Earth ground is

terminated to the secondary of the transformer neutral. Also at the pole or pad mounted transformer is this where

the primary Earth ground is located. This design leads to a different voltage rise from the primary to secondary

earth grounds when lighting, high voltage switching or changing of radial systems occur within the power

distribution system. This system will cause fluctuation of voltage with line surge. When an unbalanced line surge

occurs it produces damage to equipment in the secondary. The results can be shock hazards fire hazards, and

damage to electrical equipment. This very application is the reason the national electrical code prohibits the

primary to secondary ground electrodes from being within 6 feet of each other.

This system paved the way for the residual current device (RCD). When this device was first introduced it was

designed to cover the entire premise wiring system. The RCD was an earlier attempt by the Europeans to solve the

TT System

Located at poleor pad mounted

transformer.

TT System

Located at poleor pad mounted

transformer.

problems with the TT systems. It was called the 4X breaker. The Forex breaker trips instantaneously at four times

its rating.

As described before, the European high-voltage application allows for smaller wire size because of less amperage.

However, this can affect the fault current ratings. The smaller wire produces a larger impedance when a short-

circuit occurs. This leads to lower unavailable fault current values which could cause an explosion or fire when a

short-circuit occurs instead of just tripping the overcurrent device.

The “Swiss watch” 4x are great breakers but the basic TT problem remains.

TN networks

In a TN earthing system, one of the points in the generator or transformer is connected with earth, usually the star

point in a three-phase system. The body of the electrical device is connected with earth via this earth connection

at the transformer.

The conductor that connects the exposed metallic parts of the consumer is called protective earth (PE). The

conductor that connects to the star point in a three-phase system, or that carries the return current in a single-

phase system, is called neutral (N). Three variants of TN systems are distinguished:

TN−SPE and N are separate conductors that are connected together only near the power source.TN−CA combined

PEN conductor fulfills the functions of both a PE and an N conductor. Rarely used.TN−C−S Part of the system uses a

combined PEN conductor, which is at some point split up into separate PE and N lines. The combined PEN

conductor typically occurs between the substation and the entry point into the building, and separated in the

service head. In the UK, this system is also known as protective multiple earthing (PME), because of the practice of

connecting the combined neutral-and-earth

conductor to real earth at many locations, to

reduce the risk of broken neutrals - with a

similar system in Australia being designated as

multiple earthed neutral (MEN).TN-S:

separate protective earth (PE) and neutral (N)

conductors from transformer to consuming

device, which are not connected together at any

point after the building distribution point.TN- C:

combined PE and N conductor all the way

from the transformer to the consuming

device.TN-C-S earthing system: combined PEN

conductor from transformer to building

distribution point, but separate PE and N

conductors in fixed indoor wiring and flexible power cords. It is possible to have both TN-S and TN-C-S supplies

from the same transformer. For example, the sheaths on some underground cables corrode and stop providing

good earth connections, and so homes where "bad earths" are found get converted to TN-C-S.

TN- C.: this is one of three variations of the TN system. This system has the grounded circuit or system neutral

combined with the equipment ground protected conductor throughout the system. This is a multi-grounded

neutral system. The national electrical code does not address this type system because it is not used in the US.

TN - C System

A Multi-Grounded Neutral System

Not Used By NEC or NFPA 70

TN - C System

A Multi-Grounded Neutral System

Not Used By NEC or NFPA 70

The TN-S system has a separate ground circuit

conductor or system neutral conductor from the

equipment grounding protective conductor

throughout the system. The neutral can be

grounded in several places to the equal potential

plane and is a common application in the US

system. The TN-S- system is similar to American

grounding systems.

The TN-C-S system has a column grounded circuit or

system of mutual conductor and equipment around

the conductor for portion of the system, and has a

separate grounded circuit or system neutral

conductor and equipment grant a conductor for the

rest of the system. As you can see in the circuits above the two-phase loads are based on the TN-C system and the

single phase loads are based on the TN-S system. In the American system and equipment ground (protective

conductor) would be required from the two-phase loads to the single point grounding earth point.

Types of NEC, US, Transformer Systems

Introduction A transformer does not generate or produce electrical power it transfers electrical power. A transformer is a voltage changer. Most transformers are designed to either step voltage up or to step it down, although some are used only to isolate one voltage from another. The transformer works on the principle that energy can be efficiently transferred by magnetic induction from one winding to another winding by a varying magnetic field produced by alternating current. An electrical voltage is induced when there is a relative motion between a wire and a magnetic field. Alternating current (AC) provides the motion required by changing direction which creates a collapsing and expanding magnetic field.

TN-S-System Three Phase With

Ground

TN-S-System Three Phase With

Ground

TN-C-S-SystemTN-C-S-System

How Transformers Operate

How Transformers Operate A transformer usually consists of two insulated windings on a common iron (steel) core: The two windings are linked together with a magnetic circuit, which must be common to both windings. The link connecting the two windings in the magnetic circuit is the iron core on which both windings are wound. Iron is an extremely good conductor for magnetic fields. The core is not a solid bar of steel, but is constructed of many layers of thin steel called laminations. One of the windings is designated as the primary and the other winding as the secondary. Since the primary and secondary are wound on the same iron core, when the primary winding is energized by an AC source, an alternating magnetic field called “flux” is established in the transformer core. The flux created by the applied voltage on the primary winding induces a voltage on the secondary winding. The primary winding receives the energy and is called the input. The secondary winding discharges the energy and is called the output.

Mutual Induction

Mutual Induction If flux lines from the expanding and contracting magnetic field of one coil cut the windings of another nearby coil, a voltage will be induced in that coil. The inducing of an EMF in a coil by magnetic flux lines generated in another coil is called mutual induction. The amount of electromotive force (EMF) that is induced depends on the relative positions of the two coils. Windings The primary and secondary windings consist of aluminum or copper conductors wound in coils around an iron core, the number of “turns” in each coil will determine the voltage transformation of the transformer. Each turn of wire in the primary winding has an equal share of the primary voltage. The same voltage is induced in each turn of the secondary. Therefore, any difference in the number of turns in the secondary as compared to the primary will produce a voltage change. Winding Physical Location: In most transformers, the high voltage winding is wound directly over the low voltage winding to create efficient coupling of the two windings. NOTE: Other designs may have the high voltage winding wound inside, side-by-side or sandwiched between layers of the low voltage winding to meet special requirements.

Theory of Operation A transformer works on the principle that energy can be transferred by magnetic induction from one set of coils to another set by means of a varying magnetic flux. The magnetic flux is produced by an AC source. The coil of a transformer that is energized from an AC source is called the primary winding (coil), and the coil that delivers this AC to the load is called the secondary winding (coil). The primary and secondary coils are shown on separate legs of the magnetic circuit so that we can easily understand how the transformer works. Actually, half of the primary and secondary coils are wound on each of the two legs, with sufficient insulation between the two coils and the core to properly insulate the windings from one another and the core. A transformer will operate at a greatly reduced efficiency due to the magnetic leakage. Magnetic leakage is the part of the magnetic flux that passes through either one of the coils, but not through both. The larger the distance between the primary and secondary windings, the longer the magnetic circuit and the greater the leakage. When alternating voltage is applied to the primary winding, an alternating current will flow that will magnetize the magnetic core, first in one direction and then in the other direction. This alternating flux flowing around the entire length of the magnetic circuit induces a voltage in both the primary and secondary windings. Since both windings are linked by the same flux, the voltage induced per turn of the primary and secondary windings must be the same value and same direction. This voltage opposes the voltage applied to the primary winding and is called counter-electromotive force (CEMF).

Windings

Windings The primary and secondary windings consist of aluminum or copper conductors wound in coils around an iron core, the number of “turns” in each coil will determine the voltage transformation of the transformer.

Each turn of wire in the primary winding has an equal share of the primary voltage. The same voltage is induced in each turn of the secondary. Therefore, any difference in the number of turns in the secondary as compared to the primary will produce a voltage change.

Voltage Ratio

VP = voltage on primary coilVS = voltage on secondary coilNP = number of turns on the primary coilNS = number of turns on the secondary coil

VR = TRVoltage Ratio = Turns Ratio

Ratio 5 : 15 volt primary = 1 volt secondary

Voltage Ratio The voltage of the windings in a transformer is directly proportional to the number of turns on the coils. The ratio of primary voltage to secondary voltage is known as the voltage ratio (VR). As mentioned previously, the ratio of primary turns of wire to secondary turns of wire is known as the turns ratio (TR). By substituting into the Equation, we find that the voltage ratio is equal to the turns ratio. VR = TR A voltage ratio of 1:5 means that for each volt on the primary, there will be 5 volts on the secondary. If the secondary voltage of a transformer is greater than the primary voltage, the transformer is referred to as a "step-up" transformer. A ratio of 5:1 means that for every 5 volts on the primary, there will only be 1 volt on the secondary. When secondary voltage is less than primary voltage, the transformer is referred to as a "step-down" transformer.

Application The primary use of transformers is for the distribution of voltage from one source to another. Typically this is accomplished by either stepping up the voltage from the primary to secondary or stepping down

the voltage from primary to secondary. There are other applications for transformers that we will discuss later. Our primary focus in this text is on the power transformer each uses, and applications. The first application we will look at will be the step down transformer. In this application our goal is to determine how the source voltage (primary) steps the voltage down from a higher source of voltage to a lower voltage of use on the load (secondary) side. . If there are fewer turns in the secondary winding than in the primary winding, the secondary voltage will be lower than the primary.

Step-Up Transformers1:5 Ratio

120 Turns 600 Turns

2400 Volt

Secondary

480 Volt

Primary

If there are fewer turns in the secondary winding than in the primary winding, the secondary voltage will be lower than the primary. Three-phase transformer operation is identical except that three single-phase windings are used. These windings may be connected in wye, delta, or any combination of the two.

Delta Connection

In the delta connection, all three phases are connected in series to form a closed loop

Wye Connection

In the wye connection, three common ends of each phase are connected together at a common terminal (marked "N" for neutral), and the other three ends are connected to a three-phase line

Delta – to DeltaA

C

B

A

B

C

Wye – to - Delta

C

B

A

A

B

C

Voltage Taps As stated previously, the voltage transformation is a function of the turns ratio. It may be desirable to change the ratio in order to get rated output voltage when the incoming is slightly different than the normal voltage.

Multi-voltage Taps

As an example, suppose we have a transformer with a 4 to 1 turns ratio. With 480 volts input, the output would be 120 volts. Suppose the line voltage is

less than normal or 456 volts. This would produce an output voltage of 114 volts which is not desirable. By placing a tap in the primary winding, we could change the turns ratio so that with 456 volts input we could still get 120 volts output. This is called a primary voltage tap and standard transformers may have from two to six taps for the purpose of adjusting to actual line voltages. Multi-voltage Tap transformer has a tap 2.5% below normal and one at 5% below, it is said to have 2-2.52% full capacity below normal taps (FCBN). This would give a 5% voltage range. When the transformer has taps above normal as shown, they would be full capacity above normal (FCAN). For standardization purposes, these taps are in 2~2.5% or 5% steps. The taps are so designed that full capacity output can be obtained when the transformer is set on any of these taps. NOTE: Taps are only to be used for steady state input line variations. They are not designed to provide a constant secondary voltage when the input line is constantly fluctuating.

Application

The application called multi-tap transformers has many uses. This transformer is commonly used in power applications to resolve voltage drop or overvoltage issues. This transformer is commonly used also for lighting. It is used often wind different voltages are available for lighting up connections. This gives the end-user much more versatility to determine the type of voltage that best applies to their application.

Series - Parallel Windings

To make the basic single-phase transformer more versatile, both the primary and secondary windings can be made in two equal parts. The two parts can be reconnected either in series or in multiple (parallel). This provides added versatility as the primary winding can be connected for either 480 volts or 240 volts and the secondary winding can likewise be divided into two equal parts providing either 120 or 240 volts. (Note: there will be four leads per winding brought out to terminal compartment rather than two.) Either arrangement will affect the capacity of the transformer. Secondary windings are rated such as 120/240V and can be connected in series for 240V or in multiple for 120V or 240/120V (for 3 wire operation.) Primary windings rated with an “X” such as 240X480 can operate in series or multiple but are not designed for 3 wire operation. A transformer rated 240X480V primary, 120/240V secondary could be operated in (6) different voltage combinations.

Parallel Winding Circuits

Series and Parallel Winding Circuits (Additive or Subtractive)

It is important to note the diagrams are in series and parallel circuitry. Series windings tend to equal more voltage while parallel windings tend to subtract the voltage source. This is somewhat of a simplification of the issue but it is true. Take special note of the voltage reaction to a series or parallel circuit. From a practical standpoint we can say that parallel windings or circuitry tend to subtract from voltage output while series windings or circuitry tends to add to the voltage output.

Three-Phase Transformers Single-Phase vs Three-Phase Power Systems Most power distribution via three-phase AC systems. Generators produce electricity by rotating (3) coils or windings through a magnetic field within the

generator. These coils or windings are spaced 120 apart. As they rotate through the magnetic field they generate power, which is then sent out on three (3) lines as three-phase power. Three-phase transformers have (3) coils or windings connected in the proper sequence in order to match the incoming power and therefore transform the power company voltage to the level of voltage we need and maintain the proper phasing or polarity. Advantages of Three-Phase Power Three-phase power for industrial loads is more efficient than single-phase. Single-phase power is available between any two phases of a three-phase system, or, in some systems, between one of the phases and ground. Three-phase systems provide 173% more power than single phase systems. Three-phase power helps prevent voltage drop problems.

The Three-Phase Transformer

Core

A B C

PA PB PC

SA SB SCP = PrimaryS = SecondaryA = PhaseB = PhaseC = PhaseH1 = Primary marking on Lead or Terminal A phaseH2 = Primary marking on Lead or Terminal B phaseH3 = Primary marking on Lead or Terminal C phaseX1 = Secondary marking on Lead or Terminal A phaseX2 = Secondary marking on Lead or Terminal B phaseX3 = Secondary marking on Lead or Terminal C phaseXo = Secondary marking on Lead or Terminal Neutral

The Three-Phase Transformer In a three-phase transformer there is a three legged iron core as shown below. Each leg has a respective primary and secondary winding. The three primary windings (P1, P2, P3) will be connected at the factory to provide the proper sequence (or correct polarity) required and will be in a configuration known as “Delta”. The three secondary windings (P1, P2, P3) will also be connected at the factory to provide the proper sequence or (correct polarity) required. However, the secondary windings, depending on our voltage requirements, will be in either a “Delta” or a “Wye” configuration.

Three-Phase Transformers

The Delta has the three windings connected in a closed circuit. The ends of the windings connect together in the proper polarity. In the Wye, all three windings connect together at one point.

Windings are connected in series

Wye Connections and Circuitry4

1

2

3

4

5

6

1

2

3

5

6

In the Wye, all three windings connect together at one point. Numbers count clockwise

Winding Combinations As can be seen, the three-phase transformer actually has 6 windings (or coils) 3-primary and 3-secondary. These 6 windings will be pre-connected at the factory in one of two configurations: Configuration 1. Three Primary Windings in Delta and Three Secondary Windings in Wye NOTE: These are the designations which are marked on the leads or

terminal boards provided for customer connections and they will be located in the transformer wiring compartment. In both single and three-phase transformers, the high voltage terminations are designated with an “H” and the low voltage with an “X”.

Three Phase transformer are designed to make the winding magnetic flux of each transformer 120 out phase with each other. These configurations are commonly called wye and delta types because their vectorial relationships. These configurations can be design an installed in several types of configuration by series or parallel connections of the windings. Using trigonometry functions we can predetermine voltage, current and power capabilities of a transformer. Quick formulas for 60 hertz applications to determine the voltage, current and power are given below:

WYE Connection – Phase Amps = Phase Amps

Phase Volts x 1.732 = Line Volts or Line Voltage 1.73 = Phase Voltage

Delta Connection – Phase Voltage = Line Voltage

Phase Amps x 1.732 = Line Amps or Line Amps 1.732 = Phase Amps

Hazardous Locations

Class I, Zone 0, Zone 1, and Zone 2 hazardous (classified) locations where fire or explosion hazards may

exist due to flammable gases, vapors, or liquids.

Informational Note: For the requirements for electrical and electronic equipment and wiring for all

voltages in Class I, Division 1 or Division 2; Class II, Division 1 or Division 2; and Class III, Division 1 or

Division 2 hazardous (classified)

locations where fire or explosion

hazards may exist due to flammable

gases or vapors, flammable liquids, or

combustible dusts or fibers

The zone classification concept, based on

the standards for area classification used by

the International Electrotechnical

Commission (IEC), offers an alternative

method of classifying Class I hazardous

locations. The IEC classification scheme

includes underground mines, whereas in

the United States, mines are under the

jurisdiction of the Mine Safety and Health

Administration (MSHA) and are outside the

scope of the NEC.

Our purpose is to point out the similarities and difference between the US and European Electrical standards. This

is by no means gives all information to classify an area. The following are informational notes excerpted from the

NFPA 70, 2011 version that should be useful when determining the classification of an area based on US and

European standards.

Informational Note No. 1: It is important that the authority having jurisdiction be familiar with recorded

industrial experience as well as with standards of the National Fire Protection Association (NFPA), the

American Petroleum Institute (API), the International Society of Automation (ISA), and the International

Electrotechnical Commission (IEC) that may be of use in the classification of various locations, the

determination of adequate ventilation, and the protection against static electricity and lightning hazards.

Informational Note No. 2: For further information on the classification of locations, see NFPA 497-2008,

Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and of Hazardous

(Classified) Locations for Electrical Installations in Chemical Process Areas; ANSI/API RP 505-1997,

Hazardous (Classified) (Zone)Locations [Explosive Atmospheres]

NEC

• Arts. 500 through 505, 510, 511, 513 through 516 Hazardous (Classified) Locations [Explosive Atmospheres]

IEC

• Art. 505 of the NEC is harmonized with IEC 60079

• Hazardous Locations Are Not covered by IEC 60364

• IEC requirements for explosive atmospheres are covered by IEC 60079

Hazardous (Classified) (Zone)Locations [Explosive Atmospheres]

NEC

• Arts. 500 through 505, 510, 511, 513 through 516 Hazardous (Classified) Locations [Explosive Atmospheres]

IEC

• Art. 505 of the NEC is harmonized with IEC 60079

• Hazardous Locations Are Not covered by IEC 60364

• IEC requirements for explosive atmospheres are covered by IEC 60079

Recommended Practice for Classification

of Locations for Electrical Installations at

Petroleum Facilities Classified as Class I,

Zone 0, Zone 1, or Zone 2; ANSI/ISA-

TR(12.24.01)-1998 (IEC 60079-10-Mod),

Recommended Practice for Classification

of Locations for Electrical Installations

Classified as Class I, Zone 0, Zone 1, or

Zone 2; IEC 60079-10-1995, Electrical

Apparatus for Explosive Gas

Atmospheres, Classification of Hazardous

Areas; and Model Code of Safe Practice

in the Petroleum Industry, Part 15: Area

Classification Code for Petroleum

Installations, IP 15, The Institute of

Petroleum, London.

Informational Note No. 6: For further information on the installation of electrical equipment in hazardous

(classified) locations in general, see IEC 60079-14-1996, Electrical apparatus for explosive gas

atmospheres — Part 14: Electrical installations in explosive gas atmospheres (other than mines), and IEC

60079-16-1990, Electrical apparatus for explosive gas atmospheres — Part 16: Artificial ventilation for

the protection of analyzer(s) houses.

Classification As a guide in determining when flammable gases or vapors are present continuously or for long periods of time,

refer to ANSI/API RP 505-1997, Recommended Practice for Classification of Locations for Electrical Installations of

Petroleum Facilities Classified as Class I, Zone 0, Zone 1 or Zone 2; ANSI/ISA-TR12.24.01-1998 (IEC 60079-10 Mod),

Recommended Practice for Classification of Locations for Electrical Installations Classified as Class I, Zone 0, Zone 1,

or Zone 2; IEC 60079-10-1995, Electrical apparatus for explosive gas atmospheres, classifications of hazardous

areas; and Area Classification Code for Petroleum Installations, Model Code, Part 15, Institute of Petroleum.

The gas and vapor subdivision as described is based on the maximum experimental safe gap (MESG), minimum

igniting current (MIC), or both. Test equipment for determining the MESG is described in IEC 60079-1A-1975,

Amendment No. 1 (1993), Construction and verification tests of flameproof enclosures of electrical apparatus; and

UL Technical Report No. 58 (1993). The test equipment for determining MIC is described in IEC 60079-11-1999,

Electrical apparatus for explosive gas atmospheres — Part 11: Intrinsic safety “i.” The classification of gases or

vapors according to their maximum experimental safe gaps and minimum igniting currents is described in IEC

60079-12-1978, Classification of mixtures of gases or vapours with air according to their maximum experimental

safe gaps and minimum igniting currents.

Encapsulation “m.”

Common to both standards is Encapsulation “m.” Type of protection where electrical parts that could

ignite an explosive atmosphere by either sparking or heating are enclosed in a compound in such a way

that this explosive atmosphere cannot be ignited.

Hazardous (Classified) (Zone)Locations [Explosive

Atmospheres]NEC

• Class I

• Class II

• Class III

• Division 1 – Normally Hazardous

• Division 2 – Not Normally Hazardous

IEC

• Zone 0

• Zone 1

• Zone 2

• Divisions 1 & 2 are not addressed in the IEC

Hazardous (Classified) (Zone)Locations [Explosive

Atmospheres]NEC

• Class I

• Class II

• Class III

• Division 1 – Normally Hazardous

• Division 2 – Not Normally Hazardous

IEC

• Zone 0

• Zone 1

• Zone 2

• Divisions 1 & 2 are not addressed in the IEC

Informational Note No. 1: See ANSI/ISA-60079-18 (12.23.01)-2009, Electrical Apparatus for Use in

Class I, Zone 1 Hazardous (Classified) Locations, Type of Protection — Encapsulation “m”; IEC 60079–

18-1992, Electrical apparatus for explosive gas atmospheres — Part 18: Encapsulation “m”; and

ANSI/UL 60079-18, Electrical Apparatus for Explosive Gas Atmospheres — Part 18: Encapsulation

“m”.

Informational Note No. 2: Encapsulation is designated type of protection “ma” for use in Zone 0 locations.

Encapsulation is designated type of protection “m” or “mb” for use in Zone 1 location

The gas or vapor group order in the zone classification system is inverse of the gas or vapor groups specified in

Article 500 of the NEC. For example, Group IIC includes Article 500, Groups A and B. Determination of a gas or

vapor for the purposes of grouping includes the evaluation of the maximum safe experimental gap ratio as well as

minimum igniting current ratio. Although the maximum safe experimental gap for Group A is less than that for

Group B in some circumstances, the minimum igniting current ratio is less for hydrogen (Group B) than it is for

acetylene (Group A). This difference has been accounted for in ANSI/UL 913, Intrinsically Safe Apparatus and

Associated Apparatus for Use in Class I, II, III, Division 1, Hazardous (Classified) Locations, because it is a factor that

must be considered in the evaluation of IS apparatus.

Cross Reference of NEC, IEC and British Standards

General Requirements: No unused openings in panels, boxes, cabinets, transformers and any electrical equipment except

venting. NFPA 70, Article 110.12.(A); BS7671 – 597.1

All conductors must be identified for applicable use at each accessible point such as panels,

junction boxes, switch boxes, any cabinet, wiring trough, fixtures and equipment. Example - Green

color as equipment ground See NFPA 70, Article 210.5(A)(B)(C), 215.5, 215.12, 200.7 and

250.119; BS7671 - 514

All overcurrent protection devices such as circuit breakers, disconnects and fuse protection must

be identified at point of origin. NFPA 70, Article 110.22, Article 408.4,; BS7671 -514.8

All Receptacles/Sockets must be tested. No open grounds, reverse polarities, reverse hot and

equipment grounds, reverse neutral and equipment ground or high impedance equipment grounds

will be accepted. NFPA 70,Article 110.7 2001.11,; BS7671 – 411.7.5, 418.3.5, Table 53.2, 612.6

Power Cords (extension) must be grounded properly. Broken or removed ground prongs are not

acceptable. NFPA 70, Article 250.134,; BS7671 - 514

No open bulb fixtures (luminaires) are accepted. Fixtures must have globe or guard to protect

bulbs (luminaires) form physical damage See NFPA 70, Article 410.11,; BS7671- 422.3 & 4

Identification of Feeder Circuits. NFPA 70, Article 215.12; BS7671- 514.8

Cords and cables cannot lay on pipes, units, nails, drop-in ceiling or hooks. See NFPA 70, Article

300.11(A); BS7671-522.6-10

No cords pass through walls, ceilings doors or windows that could be pinched, strained or

subject to physical damage. See NFPA 70, Article 400.14,; BS7671 – 521.6.5

No cords pass through walls, ceilings doors or windows used as a substitute for permanent

wiring methods. See NFPA 70, Article 400.8 (1)(2)(3)(4),; BS7671 -521.6.5

All panels, junction boxes, transformers and electrical access points must be accessible. See NFPA

70, Article 110.26, 300.15, 314.29 & 30, 230.93, 240.24; BS7671 -513.1

All metal enclosures must be tested for stray (unwanted) voltage. Any stray or

unwanted voltage on surfaces of panels, cable trays, transformers, generators, enclosures

and cabinets must be removed before use. Article 110.7., NFPA 70; BS7671 – Chapter 44

Equipment deterioration must be replaced or repaired as appropriate. See NFPA 70

Article 110.11&12 (B) 33,; BS7671- 412.2.4, 561.10

Plugs must be properly attached to cords – See Article 400.14, 406.7, NFPA 70; BS7671-

553.1 Identification of Branch Circuits/Final Circuits See Article 210. 5 (C) (A)(B)(C), NFPA 70;

BS7671- 514.5, 514.8, Table 51

All equipment installed outdoors must be protected for physical damage, wet weather and

sun. See Article 300.3 (A), 300.4, 110.11, NFPA 70; BS7671- 522

All receptacles/sockets installed outdoors must have GFCI/RCD protection Article 210.8,

NFPA 70; BS7671- 411.3.3.i

All Receptacles/sockets in Wet Locations must have GFCI/RCD protection Article 210.8., 406.9

NFPA 70; BS7671- 701.411.3.3

All raceways, cables and tray in Wet Locations must have must be rated or listed for location

NFPA 70, Article 110.3, NFPA 70; BS7671- 701.55

Bushings shall be required at all conduit connectors. See Article 300.5 (H) ; 300.4(G), 300.15(C),

300.16(A)(B) NFPA 70; BS7671- 412.2.4, 561.10

Locknuts must be installed properly with nut cutting into box or cabinets Article 110.3.B,

250.134 (G)NFPA 70; BS7671-522.8, 412.2.4, 561.10

All luminaires/lighting in Wet Locations must have must be rated or listed for location.

See Article110.3.B, 410.10 NFPA 70; BS7671- 701.55(i),(viii)

Kitchens – all counter receptacles, sink receptacles must have GFCI/RCD protection

Article 210.8., NFPA 70;BS7671- 706.410.310(iii)(b)

Grommets are required at each cable entering boxes, cabinets or equipment Article

300.7.(A); 300.9, NFPA 70; BS7671- 412.2.4, 561.10

Labels shall be provided by contractor at each panel, switchboards, control panels and

motor control centers to warn qualified electrical workers of type PPE needed plus shock

and arc boundaries. See Article 110.16, NFPA 70; BS7671- 514.13, 522, 537

Expansion fittings must be used when thermal or vibration could cause damage to raceways or

equipment. See Article 300.7(B), NFPA 70; BS7671- 412.2.4, 561.10

Raceways must be secured. Ceiling support wire is not acceptable. Raceways must have

independent support. 300.11(A) NFPA 70; BS7671- 522.8.5

Conduit, cable and all raceways must have continuity and not broken without appropriate

fittings See Article 300.10, 300.12, NFPA 70; BS7671- 543.2.1, 543.3.6, 522.8.5

Raceways and cables cannot be used as a support means for anything other than

raceways, equipment or cables 300.11.(B)(C)NFPA 70; BS7671- 522.8.5

Documentation Test and Policy

Documentation of Test records for Megger Ohm Readings of Service and Feeder Conductors

must be provided and approved. NFPA 70, Article 110.7, 110.12 (B), BS7671-612.3, Table 61

Each contractor must have a written Lock Out and Tag Out procedure. Documentation of

procedure must be provided to inspector OSHA CFR 1910.147

Worker Qualification documentation –Written policy and procedure for training must be

certification or degree. See NFPA 70, Article 100, 70, NFPA 70 E Article 110.27; BS7671-560.6.2

PPE is available to workers. Verify by visual inspection of equipment. Must meet ASTM standard

must be visible on all equipment.

Documentation that smoke detectors operate properly – interlock operation should observed

via audio inspection Article 700.4,NFPA 70; BS7671-560.5.1

Labels shall be provided by contractor at each panel, switchboards, control panels and motor

control centers to warn qualified electrical workers of type PPE needed plus shock and arc

boundaries. See NFPA 70, Article 110.16, energizing and deenergizing equipment, OSHA CFR.

1910. Subpart S

Safety Training documentation of How to Control Electrical Hazards must be provided. Article

100, NFPA 70.

Voltage Drop- Obtain documentation of voltage readings at all Service and Feeder panels. No

more than 5% voltage drop for feeders and 3% for branch circuits is acceptable. NFPA 70, article

215.2, Informational Note 2; BS7671-612, 525.2, Conduct a witness test of emergency systems such as generators. NFPA 70, Article 700.4 (A) –

(E); BS7671-612.13; Chapter 63

System Test

Battery test

Load Test

All receptacles must be tested. No open grounds, reverse polarities, reverse hot and equipment

grounds, reverse neutral and equipment ground or high impedance equipment grounds will be

accepted. Article 110.7., 110.12 (B), 200.11, 250.6, 250.4(A)(5),250.4(B)(4),250.134, NFPA 70;

BS7671-612.6,612.9

All metal enclosures must be tested for stray (unwanted) voltage or step potential voltage.

Any stray or unwanted voltage on surfaces of panels, cable trays, metal water pipe,

appliances, faucets, water heaters, transformers, generators, enclosures and cabinets must be

removed before use. Any conductive path that could be energized unavailable to the public.

Article 110.7., 110.12 (B), 250.6, 250.4(A)(5),250.4(B)(4), NFPA 70; BS7671-621.2, Table

61

Electrical/Mechanical Rooms:

Panels, switchgear, transformers, fire controls, and electrical equipment must be identified Article 408.4,

110.22 NFPA 70; BS7671-514.15.1, 418.2 & 3

Doors must not be modified different to original design. Article 110.4.B, NFPA 70; BS7671-412.2.2.3

Wet locations – all equipment must be design for installation in said location. NFPA 70, Article 110.11.,

NFPA 70; BS7671- 701.55

High Voltage Signs Must Be Posted. See Article 110.34(C)NFPA 70; BS7671-514.15.1, 418.2 & 3

Deterioration of Equipment or conductors must be replaced or repaired as appropriate. See NFPA 70,

Article 110.7, 110.11; BS7671-632.4, 633.1, 634.2

Identification of Disconnects, panels (included branch circuits), motor controls centers, including starters is

required. NFPA 70, Article 408.4, 110.22; BS7671-514.15.1, 418.2 & 3

Motor, generator, pump and fire controls doors must be closed and latched. NFPA 70, Article

110.27(A)(1)(2)(3); BS7671-412.2.2.3

Disconnects, switches and circuit breakers must operate properly. Article 110.4&7, NFPA 70 ;

BS7671-537.5.2.3

Restricted Area Signs Posted – Example “this area accessible to Qualified Electrical Workers

Only” See Article 110.27(A) 1(C)NFPA 70; BS7671-410.3.5

Emergency lighting must be working properly. Illumination required. See Article 110.26.(D,

110.34.(D) NFPA 70; BS7671-110.1(xxii) Proper ventilation for electrical room as required by drawings Working Clearance/ Dedicated

Space/Headroom/ Illumination. Conditions (1or2or3) of Article 110.26 less than 600 volts and

Article 110.27 above 600 volts must be met. 110.34; BS7671-132.12, 512 &513

Identify equipment ground and protective grounds. NFPA 70, Article 250.110, 119,

NFPA70, BS7671-514.4.2

Are all enclosures bonded? Article 250.90-96, 250.110 & 112, NFPA 70, BS7671- 411.3.1.2

Metal piping systems and structures bonding requirements 250.104, NFPA 70, BS7671- 411.3.1.2

Grounding Electrodes/Earth Ground – NFPA70, Part II Article 250.50-53, BS7671 – 542.2, Part 2

Underground Installations

Raceways and cables underground must maintain a minimum cover requirement given in NFPA 70, Table

300.5 5; BS7671-522.8.10

Conductors and cables emerging from the grade or entering a building must be protected See NFPA

70, Articles 300.5(D) (1); BS7671-522.8.10

Conductors buried below grade must have ribbon installed at no less than 18” above the conductor – See

Article 300. (D)(3); BS7671-522.8.10

All underground enclosures and raceways must be protected from physical damage. See NFPA 70, Article

300.5(D) (4); BS7671-522.8.10

Raceway Seals – such as grommets must be installed to protect from moisture. See NFPA 70, Article

300.5(G), 300.7; BS7671-522.8.10

Bushings at all conduit ends. See NFPA 70, Article 300.5(H); BS7671-522.8.10

All phase conductors, neutrals, and equipment grounds must be installed in the same trench. See Article

300.5(I)

Conductors, Cables and Raceways subject to earth movement must install as “S” type loops to allow for

movement. See NFPA 70, Article 300.5(J)IN

Manhole must maintain a minimum of 900mm or 3’ work space when cables are located on both sides.

See NFPA 70, Article 110.72; BS7671-522.8.10

Manhole must maintain a minimum of 1.8 or 6’vertical clearance.. NFPA 70, Article 110. 72; BS7671-

522.8.10

Kitchen, Cafeteria, Office, Labs, Laundry, Break Rooms

Power cords arranged in neat and nonhazardous manner. NFPA 70, Article 110.12(B), 300.4, 400.8;

BS7671-521.9

No tripping hazard with cords – NFPA 70, Article 400.8; BS7671-521.9

Appliances must have permanent wiring to receptacles within pigtail length. NFPA 70, Articles

422.16(B)(1)(2), 422.16(B)(2)(2), 400.8(1), NFPA-70

Wet/Dry sinks – Adjacent receptacles must have GFCI/RCD – See AED Requirements and

NFPA 70, Article 210.8; BS7671- 411.3 Kitchen counter GFCI protection NFPA 70, Article 210.8 (A)(6)(7), 210.8 (B) (1)(2)(3)(4)(5)NFPA 70;

BS7671-521.9, 553.1.7

No cords strung in air or along walkways. Replace with permanent method NFPA 70, Article

400.8; BS7671-521.9

All receptacles in wet areas must have GFCI protection NFPA 70, Article 210.8 (A)(6)(7),210.8 (B)

(1)(2)(3)(4)(5); BS7671-701.413, 701, 512.3

All panels must be assessable NFPA 70, Article 408.20, article 240.24(A), BS7671-132.12 & 513

On/Off switches must be accessible - See NFPA 70, Article 110.26, 300.15, 314.29 314.55, 230.93,

240.2,4; BS7671 -513.1

Must meet all general requirements as applicable under “General Requirements”

Dormitories

All general requirements as applicable.

Smoke detectors must be installed each habitable area and hallways adjacent. Fire Code Smoke detectors must be interlocked Example when one detector sounds all detectors must

sound NFPA 70, Article 700.4 NFPA 70 Lighting must be operable for all exits, rooms, stairways (3way at exit and entrance) attics and

entrance See Article 210.70(A)(1); BS7671-559.6.1.5 & 9

All Receptacles in bathrooms must have GFCI/RCD protection NFPA 70, Article 210.8

(A)(6)(7), 210.8 (B) (1)(2)(3)(4)(5)NFPA 70; BS7671-521.9, 553.1.7

All luminaires/lighting in Wet Locations must be rated or listed for wet locations.

Shower lighting must be specifically listed for that area. NFPA 70, Articles 406.8 (C);

410.10; BS7671- 701.55 (viii)

All raceways, cables and tray in Wet Locations must have must be rated or listed for location.

NFPA 70, Articles 406.8 (C); 410.10; BS7671- 701.55 (viii)

Check smoke detectors for proper operation NFPA 70, Articles 700.4; BS7671-560.10

No electrical equipment allowed in shower area – switches, receptacles etc. receptacles adjacent

to sinks must have GFCI/RCD protection. NFPA70, Article 250.110, 119, BS7671-514.4.2

Are all enclosures bonded? Article 250.90-96, NFPA 70, BS7671- 411.3.1.2

Metal piping systems and structures 250.104, NFPA 70, BS7671- 411.3.1.2

Grounding Electrodes/Earth Ground – NFPA70, Part II Article 250.50-53, BS7671 – 542.2, Part

2

No luminaires installed over shower stall or tub NFPA 70, Articles 406.8 (C); 410.10; BS7671-

701.55 (viii)

Tables

Overcurrent Protection, Wire Size, Conduit Size, Protective Conductor and Equipment Ground Size

Fuse or

Circuit

Breaker

Protection

Size

Copper

Wire

60Terminal

Types - TW, UF

Copper

Wire

75 C Terminal

Types - RHW, THHW, THW,

THWN, XHHW, USE, ZW

Continuous

Ampere

Load

Conduit

Size

Protective

Conductor

Equipment

Ground

Size

AWG (mm2)

AWG (mm2)

Below

600

Volts

Above

600

Volts

15 14 (2.5mm²)

14 (2.5mm²)

12 ½” ½” 14

20 12 (4mm² )

12 (4mm² )

16 ½” ½” 12

25 10 ( 6mm²)

10 ( 6mm²)

20 ¾” ¾” 10

30 10 ( 6mm²)

10 ( 6mm²)

24 ¾” ¾” 10

35 8 (10mm² )

8 (10mm² )

28 1” 1” 10

40 8 (10mm² )

8 (10mm² )

32 1” 1” 10

45 6 (16mm² )

6 (16mm² )

36 1” 1” 10

50 6 (16mm² )

6 (16mm² )

40 1 “ 1 “ 10

60 4 (25mm² )

6 (16mm² )

48 1 “ 1 “ 10

70 4 (25mm² )

4 (25mm² )

56 1 ¼” 1 ¼” 8

80 3 (25mm² )

4 (25mm² )

64 1 ¼” 1 ¼” 8

90 2 (35mm²)

2 (35mm²)

72 1 ¼” 1 ¼” 8

100 2 (35mm² ) 2 (35mm²) 80 1 ¼” 1 ¼” 8

110 2 (35mm² ) 2 (35mm²) 88 1½ “ 1½ “ 6

125 1/0 (50mm² ) 1 (50mm² ) 100 2” 2” 6

150 2/0 (70mm² ) 1/0 (50mm² ) 120 2” 2” 6

175 3/0 (95mm² ) 2/0 (70mm² ) 140 2” 2” 6

200 4/0 (120mm² ) 3/0 (95mm² ) 160 2 ½” 2 ½” 6

225 250 (120mm² ) 4/0 (120mm² ) 180 2 ½” 2 ½” 4

250 300 (150mm² ) 250 (120mm² ) 200 3” 3” 4

300 400 (240mm² ) 350 (185mm²) 240 3 ½” 3 ½” 4

350 500 (300mm² ) 400 (240mm² ) 268 3 ½” 3 ½” 3

400 700 (400mm² ) 500 (300mm² ) 304 4” 4” 3

400 600 (300mm²) 320 4” 4” 3

Comparison of Metric to AWG Wire

Size

Overcurrent

Protection

AWG Metric AWG Metric

14 2.5mm2 15

12 4mm2 25

10 6mm2 30

8 10mm2 50 8 10mm2

6 16mm2 65 6 16mm2

4 25mm2 85 4 25mm2

3 25mm2 100 3 25mm2

2 35mm2 115 2 35mm2

1 50mm2 130 1 50mm2

1/0 50mm2 150 1/0 50mm2

2/0 70mm2 175 2/0 70mm2

3/0 95mm2 200 3/0 95mm2

4/0 120mm2 230 4/0 120mm2

250 120mm2 255 250 120mm2

300 150mm2 285 300 150mm2

350 185mm2 310 350 185mm2

400 240mm2 335 400 240mm2

500 300mm2 380 500 300mm2

600 300mm2 420 600 300mm2

700 400mm2 460 700 400mm2

800 400mm2 490 800 400mm2

AC/DC Formulas

To Find Direct Current AC/Phase to Neutral

220v,115vor120v

AC/1phase 330,208,230, or

240v

AC 3phase All Voltages

Amps when Horsepower is Known Amps when Kilowatts are known

Amps when kVA is known

HP x 746

E x Eff

kWx 1000

E

HP x 746

E x Eff X PF

kWx 1000

E x PF

kVAx 1000

E

HP x 746

E x Eff x PF

kWx1000

E x PF

kVAx1000

E

HPx746

1.73 x E x Eff x PF

kWx1000

1.73 x E x PF

kVAx 1000

1.73 x E

Kilowatts I x E

1000

I x E x PF

1000

I x E x PF

1000

I x E x 1.73PF

1000

Kilovolt-Amps I x E

1000

I x E

1000

I x E x 1.73

1000

Horsepower (output)

I x Ex Eff

746

I x E x Eff x PF

746

I x E x Eff x PF

746

I x E x Eff x 1.73 x PF

746

IntegrityInstituteCopyright2011

C&G 2382. 17th Edition (BS7671:2008) Examination (You should allow 1 hour 10 minutes for this 40 question Mock-exam)

1. The Regulations (BS7671:2008) do NOT apply to a. Residential Premises b. Industrial Premises c. Lightning Protection d. Street Furniture 2. The Regulations do apply to a. Offshore Installations b. Mines & Quarries c. Lift Installations d. Low Voltage Generators 3. Which of the Following documents are deemed Non- Statutory a. BS7671:2008 b. EAWR 1989 c. HASAW 1974 d. ESQCR 2002 4. Parts 3 – 7 of BS7671:2008 are explained in rudimentary terms within a. Chapter 13 b. Chapter 12 c. Part 3 d. Appendix 5 5. Basic protection is defined as a. Protection against shock under fault conditions b. Protection against shock under fault free conditions c. Protection against contact with live parts under fault free conditions d. Protection against faults under sound electrical conditions 6. Equipment in which protection against electric shock does not rely on basic insulation only is described as a. Double Insulated Equipment b. Class I Equipment c. Class II Equipment d. Class III Equipment 7. The Earthing System illustrated in Figure 1 below would be identified as a a. TN-S b. TT c. TN-C-S d. IT Figure 1

8. A Voltage of 250Volts AC (rms) would be defined as a. Band I b. Extra Low Voltage c. High Voltage

d. Low Voltage 9. In determining Maximum Demand, ‘Diversity’ may be applies, which is a. Taking the sum of all the protective devices from any CCU b. Taking into account that not all loads will be switched on at the same time c. Taking into account that all loads doubtless will be engaged at the same time d. Ensuring that an economical and reliable design preference is utilised. 10. Every Installation is divided into circuits in order to a. Ensue simplicity of isolation b. Comply with European Standards c. Avoid hazards and prevent inconvenience in the event of a fault d. Allow individual energising of circuits which are not isolated 11. A building made entirely out of wood would be categorised for External Influences as a. CA2 b. CA1 c. CB3 d. CB4 12. The Maximum Disconnection time for an a.c. TN circuit rated at 230V is a. 0.04 seconds b. 0.1 seconds c. 0.4 seconds d. 0.2 seconds 13. The Maximum Zs for a BSEN60898 Type C circuit breaker rated at 16Amps with a 0.4second disconnection time is a. 2.87Ω b. 1.44 Ω c. 0.72 Ω d. 1.15 Ω 14. For a TT System the Maximum earth fault loop impedance for a 100mA BSEN61008-1 RCD in a 230Volt circuit is a. 500 Ω b. 460 Ω c. 167 Ω d. 100 Ω 15. Where, on electrical equipment, must the symbol in figure 2 be present Figure 2

a. Where basic and supplementary earthing is present on an appliance b. Where supplementary earth-bonding to an appliance is not present c. Where electrical equipment has basic insulation only d. Where Class I equipment is served from a sub-main CCU 16. Where Basic Protection is employed in the form of a barrier or enclosure, any horizontal top surface must meet a protection level of at least a. IPDXX b. IP2X c. IPXX3 d. IP4X 17. Except if made from adequate material, a luminaire rated at 200Watts should be located away from combustible material by a. 0.3m b. 0.5m c. 0.8m

d. 1.0m 18. To avoid burning, a non-metallic part intended to be touched but not hand held cannot exceed a. 80°C b. 85°C c. 90°C d. 95°C 19. In relation to Voltage Disturbances, the resistance of the earthing arrangement at the Transformer is referred to, within the area of symbols, as a. RA

b. RB

c. RD

d. RE

20. Every core of a cable shall be identifiable at its terminations and preferably throughout its length by a. colour code only b. letter code only c. number code only d. one or more of the above 21. An appropriate colour for a PEN conductor should be: a. blue through its length with green markings at the terminations b. green & yellow through its length with blue markings at the terminals c. green & yellow through its length with brown markings at its terminals. d. Green through its length with yellow markings at the terminals 22. A permanent label with the words ‘Safety Electrical Connection – Do Not Remove’, complies with: a. BS728 b. BS1363 c. BS951 d. BS423 23. A cable buried underground but not in conduit or ducting for mechanical protection must incorporate a. An earthed armour or metal sheath or both b. A surface covering of 50mm thickness paving stones c. A clear surface warning notice informing of its location d. A PVC outer sheath 24. The de-rating factor for a cable surrounded by 50mm of thermal insulation is a. 0.88 b. 0.78 c. 0.63 d. 0.51 25. In an L.V installation supplied directly from a public L.V distribution system the maximum volt drop on a lighting circuit between the origin and any load point should be no greater than a. 6% Uo b. 5% Uo c. 4% Uo d. 3% Uo 26. Every electrical inspection shall be accessible for inspection, testing and maintenance purposes except for which of the following a. A connection made in a junction box beneath floorboards

b. A connection made within a motor control unit c. A connection designed to withstand fault current d. A compound filled or encapsulated joint 27. The rated RCD operating current of such a device installed as a protection against risk of fire in a TT system shall have a value of a. 30mA b. 100mA c. 300mA d. 500mA 28. The maximum prospective short circuit or earth fault current in a circuit should not exceed a. The operating current of circuit switching devices b. The rated breaking capacity of any associated protective device c. The design current of the circuit d. The rated operating current of any RCD in circuit 29. Which of the following switching devices may be satisfactorily utilised for the purposes of isolation? a. BSEN60669-2-4 b. BSEN60669-2-3 c. BSEN60669-2-1 d. BSEN60669-1 30. When using bare conductors in extra low voltage lighting installations supplied from a safety isolating transformer the minimum permissible cross sectional area of conductors must be a. 1.5mm2

b. 2.5mm2

c. 4mm2

d. 6mm2

31. Suspension devices for ELV luminaries must in any case be capable of supporting at least a. 5 Kg b. 7.5 Kg c. 10 Kg d. 20 Kg 32. An automatic electrical safety service supply classed as medium break must, in the event of losing the main supply, instate the safety service supply in a time period of a. between 0.15 & 0.5 seconds b. between 0.5 & 5 seconds c. between 5 & 15 seconds d. greater than 15 seconds 33. The minimum value of Insulation Resistance for a 230Volt system must be a. >0.25 MΩ b. >0.5 MΩ c. >1.0 MΩ d. >2.0 MΩ 34. Correct Polarity must ensure that every ES lamp-holder have their outer or screwed contacts connected to the neutral conductor, except for a. E14 & E27 Lampholders b. E14 & BSEN60895 Lampholders c. E27 & BSEN61009 Lampholders

d. E11 & E24 Lampholders 35. To comply with PART 6 of BS7671, Periodic Inspection & Testing shall be specifically undertaken by a. A formally qualified Test Engineer b. A person deemed as the ‘Duty Holder’ of the company carrying out the work c. A expressly skilled person d. A competent person 36. Zone 2 of a bathroom is restricted to the highest water outlet or the horizontal plane lying above finished floor level by a. 3.00m b. 2.50m c. 2.25m d. 2.00m 37. In Zone 3 of a Sauna equipment must be able to withstand a minimum temperature of a. 100°C b. 120°C c. 125°C d. 170°C 38. In marinas, equipment installed above a jetty or wharf, which is likely to encounter water jets, shall be selected to comply with external influence levels of a. (AD4): IPX4 b. (AD5): IPX5 c. (AD6): IPX6 d. (AE6): IPX5 39. For a BS88-2.2 Fuse rated at 25A to obtain a 0.4sec disconnection time, it would require a minimum prospective fault current of a. 160A b. 130A c. 100A d. 85A 40. A 30Amp Semi Enclosed BS3036 Fuse receiving a prospective fault current of 130A would disconnect in a. 5.0sec b. 1.0sec c. 0.4sec d. 0.2sec Answers: 1. C Part 1 -110.2 Page 13 2. D Part 1 -110.1 Page 12 3. A Part 1 -114.1 Page 13 4. A Part 1 -120.3 Page 14 5. B Part 2 - DEFENITIONS 6. B Part 2 - DEFENITIONS 7. C Part 2 - DEFENITIONS 8. D Part 2 - DEFENITIONS 9. B Part 3 - 311.1 Page 38 10. C Part 3 - 314.1 Page 39 11. A Appendix 5 Page 319 12. C Part 4 - Table 41.1 Page 46

13. B Part 4 - Max Zs Tables - Part 4 14. B Part 4 - Table 41.5 Page 50 15. C Part 4 - 412.2.1 Page 55 16. D Part 4 - 416.2.2 Page 60 17. C Part 4 - 422.3.1 Page 67 18. A Part 4 - Table 42.1 Page 69 19. D Part 4 - 442.1.2 Page 80 20. D Part 5 21. B Part 5 22. C Part 5 23. A Part 5 24. A Part 5 – Table 52.2 Page 104 25. D Part 5 26. D Part 5 27. C Part 5 28. B Part 5 29. A Part 5 30. C Part 5 31. A Part 5 32. C Part 5 33. C Part 6 - Table 61 Page 158 34. A Part 6 - 612.6 Page 159 35. D Part 6 - 621.5 Page 162 36. C Part 6 - Page 169 37. C Part 7 - 703.512.2. Page 180 38. B Part 7 - 709.512.2.1.1 Page 193 39. A Appendix - Time/Current Graph - Page 248 40. C Appendix - Time/Current Graph -Page 245

Thanks for questions contribution - djtelectraining.co.uk

Appendix 1 US and European Product Requirements

U.S. Product Requirements Corresponding to Normative References in IEC 60364 Documents

Note: The indicated locations in IEC 60364 documents are in the order given in Annex B-1. The

indicated corresponding U.S. product requirements were selected, taking into consideration the context

in which the IEC documents were referenced.

U.S. Product Requirements Location and Number of Standard

60364-1-132.5

Number, Title

60364-3-3.2

IEC 446

ANSI/NFPA 79, Electrical Standard for Industrial Machinery [contains requirements (among others) for

identification of conductors]

60364-3-3.2, Amd 2

IEC 255-22-1

IEC 801-4

IEC 1000 (all referenced parts)

UL991, Tests for Safety Related Controls Employing Solid-State Devices

Note 1: UL991 includes EMC elements of EMC evaluations contained in IEC 1000 documents. UL991

applies where referenced in a product standard, such as UL8730, which is harmonized with IEC 60730 on

automatic electrical controls for household and similar use

Note 2: All EMC emissions related requirements are contained in U.S. Federal Regulations

60364-4-411.1.2

IEC 742

UL1310, Class 2 Power Units

UL1585, Class 2 and Class 3 Transformers

UL1561, Dry-Type General Purpose and Power Transformers

60364-4-41.2, Amd 1

IEC 146-2

UL508C, Power Conversion Equipment

60364-4-43, Amd 1

IEC 60269-1, -2, -3

UL248 (series), Low-Voltage Fuses

Note: A series of 16 Standards. UL/CSA harmonized

60364-4-43, Amd 1

IEC 60898

IEC 60947-2

UL489, Molded-Case Circuit Breakers, Molded-Case Switches, and Circuit-Breaker Enclosures

60364-5-510.2

IEC 60707

UL94, Test for Flammability of Plastic Materials for Parts in Devices and Appliances

60364-5-510.2

IEC 61024-1

UL96A, Installation Requirements for Lightning Protection Systems

60364-5-510.2

IEC 332-1

UL910, Test for Cable Flame-Propagation and Smoke-Density Values

60364-5-510.2

IEC 332-3

UL1685, Vertical-Tray Fire-Propagation and Smoke-Release Test for Electrical and Optical-Fiber Cables

60364-5-510.2

IEC 439-2

UL857, Busways and Associated Fittings

UL870, Wireways, Auxiliary Gutters, and Associated Fittings

60364-5-510.2

IEC 529

UL50, Enclosures for Electrical Equipment (protection against environmental conditions only)

60364-5-510.2

IEC 614

IEC 1200-52

UL1, Flexible Metal Conduit

UL6, Rigid Metal Conduit

UL360, Liquid-Tight Flexible Steel Conduit

UL651, Schedule 40 and 80 Rigid PVC Conduit

UL651A, Type EB and A Rigid PVC and HDPE Conduit

UL1242, Intermediate Metal Conduit

UL1660, Liquid-Tight Flexible Nonmetallic Conduit

UL1684, Reinforced Thermosetting Resin Conduit

UL797, Electrical Metallic Tubing

UL1653, Electrical Nonmetallic Tubing

60364-5-523.1.2

IEC 502

UL1072, Medium-Voltage Power Cables

60364-5-527.2.1

ISO 834

UL1479, Fire Tests of Through-Penetration Firestops

60364-5-53.2

IEC 269-3

UL248 (series), Low-Voltage Fuses

60364-5-53.2

IEC 1008

IEC 1009

UL489, Molded-Case Circuit Breakers, Molded-Case Switches, and Circuit-Breaker Enclosures

UL943, Ground-Fault Circuit-Interrupters

60364-5-534.1.2

IEC 60664-1

UL840, Insulation Coordination Including Clearances and Creepage Distances for Electrical Equipment

60364-5-548.1.2

IEC 950, Amds 1 & 2

UL1950, Standard for Safety for Information Technology Equipment

60364-7-701.53, Note

IEC 669-1

UL20, General-Use Snap Switches

60364-7-702.12

IEC 60245-1, -4

UL44, Thermoset-Insulated Wires and Cables

UL62, Flexible Cord and Fixture Wire

UL676, Underwater Lighting Fixtures

60364-7-704.511.1

IEC 439-4

UL231, Power Outlets

60364-7-707, Preface

IEC 83

IEC 614-2-1

UL1681, Wiring Device Configurations

ANSI/NEMA WD 6, Wiring Devices—Dimensional Requirements

UL1682, Plugs, Receptacles, and Cable Connectors of the Pin and Sleeve Type

UL1686, Pin and Sleeve Configurations

UL6, Rigid Metal Conduit

60364-7-708, Preface

IEC 309-1

IEC 309-2

IEC 695-2-1

UL1686, Pin and Sleeve Configurations

ANSI/NFPA 501C, Recreational Vehicles

UL746, Polymeric Materials—Short Term Property Evaluations

60364-7-709.12

IEC 38

IEC 227

ANSI C 84.1, Electric Power Systems and Equipment—Voltage Ratings (60 Hz)

UL83, Thermoplastic Insulated Wires and Cables

60364-7-711.1.2

IEC 60204-1

IEC 61046

ANSI/NFPA 79, Electrical Standard for Industrial Machinery

UL508, Industrial Control Equipment

UL2108, Low-Voltage Lighting Systems (under consideration)

60364-7-714.12

IEC 598

UL1570, Fluorescent Lighting Fixtures

UL1571, Incandescent Lighting Fixtures

UL1572, High Intensity Discharge Lighting Fixtures

Annex C

Excerpts From ISO/IEC Directives, Part 3, 1997

6.5.1 Notes and examples integrated in the text

Notes and examples integrated in the text of a standard shall only be used for giving additional

information intended to assist the understanding or use of the standard and shall not contain provisions

to which it is necessary to conform in order to be able to claim compliance with the standard.

6.6.1 Verbal forms for the expression of provisions

6.6.1.1 A standard does not in itself impose any obligation upon anyone to follow it. However, such an

obligation may be imposed, for example, by legislation or by a contract. In order to be able to claim

compliance with a standard, the user needs to be able to identify the requirements he is obliged to

satisfy. He needs also to be able to distinguish these requirements from other provisions where he has

a certain freedom of choice.

6.6.1.2 Clear rules for the use for verbal forms (including modal auxiliaries) are therefore essential.

6.6.1.3 Annex E gives, in the first column of each table, the verbal form that shall be used to express

each kind of provision. The equivalent expressions given in the second column shall be used only in

exceptional cases when the form given in the first column cannot be used for linguistic reasons.

Verbal forms for the expression of provisions of ISO/IEC Directives, Part 3, 1997 (normative)

Note: Only singular forms are shown.

The verbal forms shown in the Requirement Table shall be used to indicate requirements strictly to be

followed in order to conform to the standard and from which no deviation is permitted.

Requirement

Verbal form

Equivalent expressions for use in exceptional cases (see 6.6.1.3)

Shall

is to

is required to

it is required that

has to

only…is permitted

it is necessary

shall not

is not allowed [permitted] [acceptable] [permissible]

is required to be not

is required that…be not

is not to be

Do not use “must” as an alternative for “shall.” (This will avoid any confusion between the requirements

of a standard and external statutory obligations.)

Do not use “may not” instead of “shall not” to express a prohibition.

To express a direct instruction, for example, referring to steps to be taken in a test method, use the

imperative mood in English.

EXAMPLE: “Switch on the recorder.”

Annex D

Example Circuits

The following two example circuits are typical of circuits installed in one-or two-family dwellings in the

U.S. The circuits are NEC compliant. These examples were analyzed by David Latimer, chairman of IEC

TC64, which is responsible for IEC 60364. Latimer’s analysis follows each of the two examples.

Additional commentary on the analysis is provided from the U.S. perspective.

Example No. 1

Central Air Conditioner (outdoor section) consisting of a hermetic motor compressor with inherent

overload protection and a fan motor (thermally protected). [Sec. 440-52]

Applicable

NEC Section

Ratings

Voltage: 230V, 1-ph, 60Hz (115V to ground) 250-20(b), 440-4

Supply System: Type TNS 250-20(b)

Compressor: 26.9A—Rated Load Amperes (RLA) 440-4

156.0A—Locked Rotor Amperes (LRA) 440-4

Fan: 1.4A—Full Load Amperes (FLA) 440-4

Marked Minimum Circuit Ampacity (MCA): 35A 440-33

[MCA = 1.25 RLA + FLA]

Marked Maximum Fuse Size: 50A 440-22

Note: Fuse Rating could be 60A, per UL1995;

manufacturer chose 50A

Location:

Outdoor, 1 m from building; unit provides physical protection for

wiring to fused switch

Wiring System, Unit to Switch: T310-13, 351-4

Type THWN conductors in liquidtight flexible nonmetallic

conduit in free air

Conductors: 2 circuit conductors, No. 10 AWG T310-16

1 protective earthing (grounding), No. 10 AWG 250-122

Insulation: 0.020 in. PVC plus 0.004 in. Nylon, rated 75C

Conductor properties: No. 10 AWG = 10380 cmils Chapter 9, Table 8

(1975 cmil = 1 mm²)

DC resistance = 1.24 ohms / 1000 ft. Chapter 9, Table 8

Conduit: App. Chapter, Table C5

Liquidtight flexible nonmetallic conduit (Type B),

3/8 in. trade size, 0.494 in. ID, 1.2 m long

Fused Switch:

Rated 60A, 240V ac 440-12, 440-14

Fuse: 50A, Class RK5, nonrenewable cartridge type

Between threshold and 50 kA: Ip = 20 kA, max.

I²t = 200,000 A²s, max.

(based on certification information)

Wiring System, Switch to Panelboard: T310-16

Cable: Consists of 2 Type THWN, No. 10 AWG conductors in steel armor

(Type AC Cable), 2 in. thermal insulation on each side (in wall)

Total length 60 ft.

Armor serves as protective earthing conductor 250-118

Maximum DC resistance of armor: 1.38 ohms per 75 m

(based on UL4)

Overcurrent Protection in Panelboard:

50A circuit breaker 440-22

Available short-circuit current: 20 kA

Analysis of Example No. 1 Under Rules of IEC 60364

Example No. 1: Air Conditioner Unit

Ampacity of cables 35A

Circuit breaker rating 50 amps. Cables not protected against overload, but A/C unit has built-in overload

protection. The separate overload and short-circuit protection rules can be invoked. We need to know

the I²t of the CB, which I do not have, but a rule of thumb is that a protective device protects a cable

with an ampacity of half the rating of the CB. Therefore, this is probably satisfactory.

There is a need to calculate the Earth Fault Loop Impedance (EFLI) and thus the I²t from the fuse or CB

characteristics.

Fuse to A/C:

EFL formed by two 10 AWG wires

Resistance: 2 x 1.24 / k ft.

Length: 4 ft.

Resistance: 2 x 1.24 x 4 / 1000 = 0.01 ohms

CB to Switch:

EFL formed by 10 AWG wire and armouring

Resistance of armouring:

1.38 ohms / 75 M = 1.38 x 1000 / 75 / 3.28 = 5.6 ohms / 1000 ft.

Length: 60 ft.

EFL resistance: (5.6 + 1.24) x 60 / 1000 = .41 ohms

External loop impedance (assumed): 0.3 ohms

[External loop impedance is the impedance from the supply service to the service equipment. This

impedance, plus the impedances of the live conductor up to the point of fault and the protective

conductor from the fault to the service, comprises the Earth Fault Loop Impedance]

Total EFLI: 0.01 + 0.41 + 0.3 = 0.72 ohms

EF current: 115 / 0.72 = 161 A

Disconnecting time (fuse): 20 seconds

Disconnecting time (CB): 3–12 seconds

Permitted disconnecting time is five seconds, therefore the circuit does not comply if the CB is at the top

limit of its characteristic; in actual fact, it would probably comply because manufacturers usually make

to the lower edge of the characteristic.

Load current: 26.9 + 1.4 = 28.3

Circuit resistance: 1.24 x 2 x 63 / 1000 = 0.156

Voltage drop: 0.156 x 28.3 = 4.42 V = 1.92%

Note 1: The fuse does not discriminate against the CB.

Note 2: Because there is no discrimination, the whole circuit is protected against earth fault by the CB,

so we must check its tripping time using the EFLI for the whole circuit. In this case, the fuse to A/C unit

is so short that the difference between the EFLI of the whole circuit and that of the circuit from the CB

to the fuse is negligible insofar as its effect on the tripping time is concerned. But if the difference in the

EFLI was greater and there was discrimination, then it would be possible to ascertain the tripping time

for a fault on the CB to fuse section of the circuit.

Maximum touch voltage: (5.6 x 60 / 1000 + 0.15) / 0.72 x 115 = 78 V

Example No. 2: Kitchen and Dining Room Receptacle Circuit

Applicable

NEC Section

Ratings

Voltage: 20A, 120V, 60Hz, one side grounded 210-6, 210-52(b)

Overcurrent Protection: 20A circuit breaker 240-3(d)

Supply System: TNS 250-20(b)

Calculated Load: 1500 VA 220-16

Receptacles: 4-duplex in kitchen

5-duplex in dining room

Shock Hazard Protection 210-8

All kitchen receptacles protected by a receptacle type ground-fault

circuit-interrupter (4-6 mA); dining room receptacles not protected by a GFCI

Cable

Type NM

2 Type THHN, No. 12 Cu conductors; 1 bare No. 12 T310-16,

grounding (earthing) conductor in PVC Jacket 240-3(d), 250-122

Conductors T310-13; Chapter 9, Table 8

No. 12 AWG THHN (0.015 in PVC + 0.004 in. Nylon)

[No. 12 Cu = 6530 cmils (1975 cmils = 1 mm²),

DC resistance - 1.98 ohms / 1000 ft.]

Installed in uninsulated 10 cm wide wall cavities, through centers of wood studs 336-4

Wall surfaces: 1/2 in. gypsum wallboard

Total length of circuit: 75 ft.

Analysis of Example No. 2 Under Rules of IEC 60364

Example No. 2: Kitchen and Dining Room Receptacle Circuit

Load: 1500 VA (assessed) There are no rules in IEC as to how this is done;

it is done differently in different countries

Current: 12.5A

Cable: 12 AWG

Ampacity: 25 A [Limited to 20 A by Sec. 240-3(d)]

Length: 75 ft.

Earth Fault Loop (EFL) formed by two 12 AWG wires

Resistance of 12 AWG: 1.98 ohms / k ft.

Earth Fault Loop Impedance (EFLI) of wires: 2 x 1.98 x 75 / 1000 = 0.3 ohms

External EFLI (assumed): 0.3 ohms

EF current: 120 / 0.6 = 200A

Disconnecting time for type 730-3 CB: 0.4 seconds max

Permitted disconnecting time at 120 V: 0.8 seconds

Therefore, the circuit complies.

Load current: 12.5 A

Circuit resistance: 0.3 ohms

Voltage drop: 0.3 x 12.5 = 3.75 = 3.26%

These disconnecting times are based on characteristics supplied by manufacturers.

Commentary on Analysis of Example Circuits

General: Comments in the analysis of Example No. 1 indicate that where separate overload and short-

circuit protective devices are provided, which is the case in this example, short-circuit protection can be

provided by a device with a rating of twice that of the ampacity of conductors (“rule of thumb”). Under

the NEC hermetic motor compressors may be protected at up to 225% of the motor rated-load current.

Since the ampacity of the conductors has to be at 125% of the RLA, the 2x rule of thumb is not

exceeded. However, short-circuit and ground-fault protection at higher levels is permitted for other

types of motors under Art. 430 of the NEC.

Considerable amount of information is needed under the IEC 60364 rules for installations that may be

considered routine under the NEC.

Information is needed to be able to calculate the Earth Fault Loop Impedance (EFLI) which includes the

service conductors, any feeders (distribution circuits), branch circuits (final circuits), and equipment

ground return paths, such as conduit, cable armor, or equipment grounding (protective) conductors.

From these values and the circuit voltage to ground maximum earth fault current is calculated. This

current is then related to overcurrent device trip curves from which the disconnecting times are

determined. The disconnecting time is an indication of the length of time during which hazardous

voltages exist on electrical equipment.

The disconnecting times so calculated are valid only for a bolted fault at the assumed fault location—

whether at a socket outlet or terminals of current-using equipment. If there is an arcing fault, there is

an approximate 40 V arc-voltage drop, which reduces the earth fault current. Also, if extraneous metal

bridges a phase conductor and an earthed part, the EFLI will be higher. In either case, the disconnecting

time calculations are no longer valid and longer disconnecting times are very likely.

The foregoing calculations are made over a concern for protection against shock hazard due to indirect

contact as specified in Sec. 413 and Clause 533.3. The potential shock hazard voltages exist on

accessible metal parts only for the duration of the fault condition and only until the OC device opens the

circuit. Normally persons do not remain in contact with exposed metal parts of fixed or stationary

equipment for extended periods of time. Therefore, there is potential for shock hazard only if a person

happens to be in contact with the equipment during the existence of the shock hazard voltage.

In situations where it is necessary for a person to be in contact with electrical equipment such as

industrial machinery, other means of protection against electric shock are specified by IEC Standards as

well as NEC and other NFPA documents. Likewise, at swimming pools and locations where persons are

immersed in water, other measures of protection, e.g. GFCIs under the NEC and RCDs under IEC 60364,

and stringent bonding rules are specified.

The concern over protection against indirect contact is appropriate if a hazardous touch voltage exists

between simultaneously accessible conductive parts. Clause 413.1.1.1 indicates this voltage to be 50 V

ac or higher. Ostensibly, where the possible touch voltages are lower, there should be no concern over

the disconnecting times. Yet the second paragraph of 413.1.1.1 and 413.1.3.5 indicates that

disconnecting times not exceeding five seconds, irrespective of the touch voltage, are permitted for

distribution (feeder) circuits and final (branch) circuits supplying stationary equipment only. (Table 41A

specifies disconnecting times between 0.8 and 0.1 seconds for circuits at 120 to over 400 V for circuits

with socket outlets.) It is not clear why, from a shock hazard standpoint, the disconnecting time is

significant when a hazardous voltage is not present.

Example No. 1

The TC64 Chairman’s analysis indicates a touch voltage of 78 V, therefore, under the IEC rules, the

disconnecting time calculations have been made. In the analysis, an external (service) loop impedance

of 0.3 ohms has been assumed. It appears that this assumption has been influenced by the

characteristics of European supply systems. Typically in the U.S., residences with a central air

conditioner are provided with a 200 A service. Even if the service conductors were 100 ft. (30.5 m) long,

the external loop impedance would be only 0.019 ohms (2/0 cu conductors, 0.0967 ohms / k ft.). Using

this value in the analysis, the total EFLI for the A/C circuit becomes 0.439 ohms and the EF current

becomes 262 A (238 A if a 100 A service is assumed). A review of fuse and CB characteristics shows that

the disconnecting times would be within five seconds.

Note 2 in the analysis addresses discrimination between the fuse and the circuit breaker. In the U.S. the

vast majority of branch circuits have overcurrent protection is provided by circuit breakers. In this

example the fuses provide protection for the equipment. In some cases, equipment markings specify

fuse protection. [In other cases specially marked (HACR) circuit breakers may be used if the equipment

markings so permit.] Coordination between the two types of OC devices is not necessary because each

serves a different purpose.

Example No. 2

The analysis points out that load calculation (assessment) is not covered by IEC rules, but different

countries address it differently. Other than ampacity of the conductors and the rating of the OC device,

the calculated load has no effect on the remainder of the example.

In this case, the EFLI is calculated to the last socket outlet on the circuit. Provision of GFCI protection (4-

6 mA) for the kitchen socket outlets means that the kitchen part of the circuit is protected from shock

hazard due to indirect contact. Assuming a circuit length of 50 ft. to the last dining room socket outlet

(no GFCI protection) and a fault at the last dining room outlet, the earth fault current would be

approximately 240 A. The 20 A circuit breaker would function in even less than 0.4 seconds, judging

from the information for the quoted 730-3 circuit breaker and known performance of U.S. circuit

breakers.

If the circuit in this example is connected to the same distribution panelboard as the circuit in Example

No. 1, and the service is rated 200 A, the external (service) loop impedance would also be lower than 0.3

ohms, and the EF current would be much higher. Shorter yet disconnecting times would be

encountered.

Acknowledgements: