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© M. J. Maytum 2016 IEC 60950 and IEC 62368 safety standard terminology

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IEC 60950 and IEC 62368 safety standard terminology

The document content is of a general nature only and is not intended to address the specific

circumstances of any particular individual or entity; nor be necessarily comprehensive, complete,

accurate or up to date; nor represent professional or legal advice. Much of the term and definition

information used in this document can be found in the IEC Glossary as of 04-2016.

Summary

This document compares the terms, definitions and parameters of the IEC 60950-1 and IEC

62368-1. Ultimately IEC 60950-1 should be replaced by the IEC 62368-1 hazard-based safety

standard and so it is important to understand the relationships between the established and

hazard-based terminology.

This document lists the IEC 60950-1 and IEC 62368-1 safety standard approaches in clause 1.

The definitions in clause 2 are grouped by root term; Persons, Safeguard, Conditions, Access,

Cable and Enclosure, Insulation, Circuit, Voltage and current, Remote, Network, Touch, and

Mains. Clause 2 covers the IEC 60950-1 voltage source parameters and clause 3 the IEC 62368-

1 voltage source, energy source, power source and potential ignition source parameters. Clause 4

shows how to create a harmonised definition using both IEC 60950-1 and IEC 62368-1

terminology. Appendix I covers IEC 60950-1 voltages, Appendix II covers IEC 62368-1

electrical source parameters and Appendix III is the Safety equivalence of IEC 60950-1 and IEC

62368-1.

http://std.iec.ch/terms/terms.nsf/welcome?OpenForm


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CONTENTS

1 IEC 60950-1 and IEC 62368-1 safety standard standards and approaches ........................... 3

1.1 IEC 62368-1 three block model .............................................................................. 3

1.2 Companion Standards .............................................................................................. 3

2 Terms ..................................................................................................................................... 3

2.1 Persons ..................................................................................................................... 3

2.2 Safeguard (unique to IEC 62368-1) ........................................................................ 4

2.3 Conditions (IEC 62368-1) ....................................................................................... 5

2.4 Access ...................................................................................................................... 5

2.5 Cable and Enclosure ................................................................................................ 6

2.6 Insulation ................................................................................................................. 6

2.7 Circuit ...................................................................................................................... 7

2.8 Voltage and current ................................................................................................. 8

2.9 Remote ..................................................................................................................... 9

2.10 Network ................................................................................................................... 9

2.11 Touch ....................................................................................................................... 10

2.12 Mains ....................................................................................................................... 10

3 IEC 62368-1 Energy Sources ................................................................................................ 11

3.1 Abbreviations .......................................................................................................... 11

3.2 ES (Energy source) .................................................................................................. 11

3.3 PS (Power source) ................................................................................................... 12

3.4 PIS (Potential ignition source) ................................................................................ 13

4 Harmonising Example ........................................................................................................... 13

4.1 Existing definitions in standards ............................................................................. 13

4.2 Harmonised definition for the RFT circuit term ..................................................... 14

Appendix I IEC 60950-1 voltages .................................................................................................... 15

Appendix II IEC 62368-1 electrical source parameters .................................................................... 16

Appendix III Safety equivalence of IEC 60950-1 and IEC 62368-1 ................................................ 19


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IEC 60950 and IEC 62368 safety standard terminology

1 IEC 60950-1 and IEC 62368-1 safety standard standards and approaches

Both documents are by IEC Technical Committee 108.

IEC 60950-1:2005+AMD1:2009+AMD2:2013 CSV: Information technology equipment -

Safety – Part 1: General requirements

- Prescriptive basic requirements for the safety of information technology equipment.

IEC 62368-1:2014: Audio/video, information and communication technology equipment - Part

1: Safety requirements

- Technology neutral approach to hazards by defining a three-block model.

1.1 IEC 62368-1 three block model

Energy is not always the hazard; it may be current or charge

The unsafeguarded “Energy” is classified into three levels

1. Not painful, but may be detectable or ignition not likely

2. Painful, but not an injury or ignition possible, but limited growth and spread of fire.

3. Injury or ignition likely, rapid growth and spread of fire.

Defined energy sources are: Electrical, Thermal (touch or fire), Chemical reaction, Kinetic and

Radiated. Most of these threats have levels of 1, 2 and 3.

1.2 Companion Standards

IEC 60950-21:2002: Information technology equipment - Safety - Part 21: Remote power

feeding

IEC 62368-3 Ed. 1.0 (Work in Progress): Audio/video, information and communication

technology equipment - Safety - Part 3: Remote power feeding

IEC TR 62368-2:2015: Audio/video, information and communication technology equipment -

Part 2: Explanatory information related to IEC 62368-1

2 Terms

2.1 Persons

service person [IEC 60950-1]: person having appropriate technical training and experience

necessary to be aware of hazards to which that person may be exposed in performing a task and

of measures to minimize the risks to that person or other persons

Energy sourcecapable of

causing pain or injury or damage

Energy transferlimited by safeguard

Body part orproperty


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user [IEC 60950-1]: any person, other than a service person. NOTE: The term user in this standard is the same as the term operator and the two terms can be

interchanged

instructed person [IEC 62368-1]: person instructed or supervised by a skilled person as to

energy sources and who can responsibly use equipment safeguards and precautionary safeguards

with respect to those energy sources Note 1 to entry: Supervised, as used in the definition, means having the direction and oversight of the

performance of others.

ordinary person [IEC 62368-1]: person who is neither a skilled person nor an instructed person

skilled person [IEC 62368-1]: person with relevant education or experience to enable him or

her to identify hazards and to take appropriate actions to reduce the risks of injury to themselves

and others

As the standards don’t use the same people terms we have user, ordinary person, instructed

person, service person and skilled person. User and ordinary person can be regarded as

equivalent as can be service person and skilled person. Instructed person is special to [IEC

62368-1].

2.2 Safeguard (unique to IEC 62368-1)

basic safeguard: safeguard that provides protection under normal operating conditions and

under abnormal operating conditions whenever an energy source capable of causing pain or

injury is present in the equipment

double safeguard: safeguard comprising both a basic safeguard and a supplementary safeguard

equipment safeguard: safeguard that is a physical part of the equipment

installation safeguard: safeguard that is a physical part of a man-made installation

instructional safeguard: instruction invoking specified behaviour

personal safeguard: personal protective equipment that is worn on the body and that reduces

exposure to an energy source Note 1 to entry: Personal protective equipment (PPE) is a form of a personal safeguard. Examples are

shields, goggles, gloves, aprons, face masks or breathing apparatus.

precautionary safeguard: instructed person behaviour to avoid contact with or exposure to a

class 2 energy source based on supervision or instructions given by a skilled person

reinforced safeguard: single safeguard that is operational under: normal operating conditions;

abnormal operating conditions; and single fault conditions

safeguard: physical part or system or instruction specifically provided to reduce the likelihood

of pain or injury, or, for fire, to reduce the likelihood of ignition or spread of fire Note 1 to entry: See 0.5 for further explanation of a safeguard.

skill safeguard: skilled person behaviour to avoid contact with or exposure to a class 2 or class 3

energy source based on education and experience

supplementary safeguard: safeguard applied in addition to the basic safeguard that is or

becomes operational in the event of failure of the basic safeguard


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2.3 Conditions (IEC 62368-1)

abnormal operating condition: temporary operating condition that is not a normal operating

condition and is not a single fault condition of the equipment itself Note 1 to entry: Abnormal operating conditions are specified in Clause B.3.

Note 2 to entry: An abnormal operating condition may be introduced by the equipment or by a person.

Note 3 to entry: An abnormal operating condition may result in a failure of a component, a device or a

safeguard.

normal operating condition: mode of operation that represents as closely as possible the range

of normal use that can reasonably be expected Note 1 to entry: Unless otherwise stated, the most severe conditions of normal use are the most

unfavourable default values as specified in Clause B.2.

Note 2 to entry: Misuse is not covered by normal operating conditions. Instead, it is covered by abnormal

operating conditions.

overload condition: abnormal operating condition or single fault condition where the load

stresses the equipment or circuit beyond normal operating conditions, but does not, immediately,

result in a non-operating state

single fault condition: condition of equipment with a fault under normal operating condition of

a single safeguard (but not a reinforced safeguard) or of a single component or a device Note 1 to entry: Single fault conditions are specified in Clause B.4.

2.4 Access

operator access area [IEC 60950-1]: part of the equipment to which, under normal operating

conditions, one of the following applies: access can be gained without the use of a tool; the

means of access is deliberately provided to the operator; the operator is instructed to enter

regardless of whether or not a tool is needed to gain access. The terms "access" and "accessible",

unless qualified, relate to an operator access area as defined above.

restricted access location [IEC 60950-1]: location for equipment where both of the following

apply: access can only be gained by service persons or by users who have been instructed about

the reasons for the restrictions applied to the location and about any precautions that shall be

taken; and access is through the use of a tool or lock and key, or other means of security, and is

controlled by the authority responsible for the location NOTE The requirements for equipment intended for installation in restricted access locations are the same

as for operator access areas, except as given in 1.7.14, 2.1.3, 4.5.4, 4.6.2 and 5.1.7.

service access area [IEC 60950-1]: part of the equipment, other than an operator access area,

where it is necessary for service persons to have access even with the equipment switched on

restricted access area [IEC 62368-1]: area accessible only to skilled persons and instructed

persons with the proper authorization

accessible [IEC 62368-1]: touchable by a body part Note 1 to entry: A body part is represented by one or more of the probes specified in Annex V, as

applicable.


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2.5 Cable and Enclosure

interconnecting cable [IEC 60950-1]: cable used to: electrically connect an accessory to a unit

of information technology equipment, interconnect units in a system, or connect a unit to a

telecommunication network or to a cable distribution system. Such a cable may carry any type of

circuit from one unit to another. NOTE A power supply cord for connection to the mains supply is not an interconnecting cable.

electrical enclosure [IEC 60950-1]: part of the equipment intended to limit access to parts that

may be at hazardous voltages or hazardous energy levels or are in TNV circuits

fire enclosure [IEC 60950-1]: part of the equipment intended to minimize the spread of fire or

flames from within

electrical enclosure [IEC 62368-1]: enclosure intended as a safeguard against electrically-

caused injury [SOURCE: IEC 60050 195:1998, 195-06-13, modified – the term safeguard has been used]

fire enclosure [IEC 62368-1]: enclosure intended as a safeguard against the spread of fire from

within the enclosure to outside the enclosure

2.6 Insulation

basic insulation [IEC 60950-1]: insulation to provide basic protection against electric shock

basic insulation [IEC 62368-1]: insulation to provide a basic safeguard against electric shock Note 1 to entry: This concept does not apply to insulation used exclusively for functional purposes.

double insulation [IEC 60950-1]: insulation comprising both basic insulation and

supplementary insulation

double insulation [IEC 62368-1]: insulation comprising both basic insulation and

supplementary insulation [SOURCE: IEC 60050-195, Amendment 1:2001, 195-06-08]

functional insulation [IEC 60950-1]: insulation that is necessary only for the correct

functioning of the equipment NOTE functional insulation by definition does not protect against electric shock. It may, however, reduce

the likelihood of ignition and fire.

functional insulation [IEC 62368-1]: insulation between conductive parts which is necessary

only for the proper functioning of the equipment

reinforced insulation [IEC 60950-1]: single insulation system that provides a degree of

protection against electric shock equivalent to double insulation under the conditions specified in

this standard NOTE The term "insulation system" does not imply that the insulation has to be in one homogeneous

piece. It may comprise several layers that cannot be tested as basic insulation and supplementary

insulation.

reinforced insulation [IEC 62368-1]: single insulation system that provides a degree of

protection against electric shock equivalent to double insulation

solid insulation [IEC 60950-1]: material that provides electrical insulation between two

opposite surfaces, not along an outer surface


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NOTE The required properties of solid insulation are specified either as: the actual minimum distance

through the insulation (see 2.10.5.2), or by other requirements and tests in this standard instead of a

minimum distance.

solid insulation [IEC 62368-1]: solid insulating material placed between two conductive parts

or between a conductive part and a body part

supplementary insulation [IEC 60950-1]: independent insulation applied in addition to basic

insulation in order to reduce the risk of electric shock in the event of a failure of the basic

insulation

supplementary insulation [IEC 62368-1]: independent insulation applied in addition to basic

insulation to provide a supplementary safeguard for fault protection against electric shock

2.7 Circuit

ELV circuit [IEC 60950-1]: secondary circuit with voltages between any two conductors of the

circuit, and between any one such conductor and earth (see 1.4.9), not exceeding 42,4 V peak, or

60 V d.c., under normal operating conditions, which is separated from hazardous voltage by

basic insulation, and which neither meets all of the requirements for an SELV circuit nor meets

all of the requirements for a limited current circuit

limited current circuit [IEC 60950-1]: circuit that is so designed and protected that, under both

normal operating conditions and single fault conditions, the current that can be drawn is not

hazardous NOTE The limit values of currents under normal operating conditions and single fault conditions (see

1.4.14) are specified in 2.4.

primary circuit [IEC 60950-1]: circuit that is directly connected to the AC mains supply It

includes, for example, the means for connection to the AC mains supply, the primary windings

of transformers, motors and other loading devices. NOTE Conductive parts of an interconnecting cable may be part of a primary circuit as stated in 1.2.11.6.

secondary circuit [IEC 60950-1]: circuit that has no direct connection to a primary circuit and

derives its power from a transformer, converter or equivalent isolation device, or from a battery NOTE Conductive parts of an interconnecting cable may be part of a secondary circuit as stated in

1.2.11.6.

external circuit [IEC 62368-1]: electrical circuit that is external to the equipment and is not

mains Note 1 to entry: An external circuit is classified as ES1, ES2 or ES3, and PS1, PS2, or PS3.

SELV circuit [IEC 60950-1]: secondary circuit that is so designed and protected that under

normal operating conditions and single fault conditions, its voltages do not exceed a safe value NOTE 1 The limit values of voltages under normal operating conditions and single fault conditions (see

1.4.14) are specified in 2.2. See also Table 1A.

NOTE 2 This definition of an SELV circuit differs from the term "SELV system" as used in IEC 61140

TNV-1 circuit [IEC 60950-1]: TNV circuit whose normal operating voltages do not exceed the

limits for an SELV circuit under normal operating conditions and on which overvoltages from

telecommunication networks and cable distribution systems are possible


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TNV-2 circuit [IEC 60950-1]: TNV circuit whose normal operating voltages exceed the limits

for an SELV circuit under normal operating conditions and which is not subject to overvoltages

from telecommunication networks

TNV-3 circuit [IEC 60950-1]: TNV circuit whose normal operating voltages exceed the limits

for an SELV circuit under normal operating conditions and on which overvoltages from

telecommunication networks and cable distribution systems are possible

TNV circuit [IEC 60950-1]: circuit that is in the equipment and to which the accessible area of

contact is limited and that is so designed and protected that, under normal operating conditions

and single fault conditions (see 1.4.14), the voltages do not exceed specified limit values . A

TNV circuit is considered to be a secondary circuit in the meaning of this standard. NOTE 1 The specified limit values of voltages under normal operating conditions and single fault

conditions (see 1.4.14) are given in 2.3.1. Requirements regarding accessibility of TNV circuits are given

in 2.1.1.1.

NOTE 2 Conductive parts of an interconnecting cable may be part of a circuit as stated in 1.2.11.6. TNV

circuits are classified as TNV-1 circuits, TNV-2 circuits and TNV-3 circuits as defined in 1.2.8.12,

1.2.8.13 and 1.2.8.14.

NOTE 3 The voltage relationships between SELV and TNV circuits are shown in Table 1A.

2.8 Voltage and current

hazardous voltage [IEC 60950-1]: voltage exceeding 42,4 V peak, or 60 V d.c., existing in a

circuit that does not meet the requirements for either a limited current circuit or a TNV circuit

limited current circuit [IEC 60950-1]: circuit that is so designed and protected that, under both

normal operating conditions and single fault conditions, the current that can be drawn is not

hazardous NOTE The limit values of currents under normal operating conditions and single fault conditions (see

1.4.14) are specified in 2.4.

protective current rating [IEC 60950-1]: rating of an overcurrent protective device that is

known or assumed to be in place to protect a circuit NOTE Rules to determine the value of the protective current rating are in 2.6.3.3.

rated current [IEC 60950-1]: input current of the equipment as declared by the manufacturer

required withstand voltage [IEC 60950-1]: peak voltage that the insulation under

consideration is required to withstand

telecommunication network transient voltage [IEC 60950-1]: highest peak voltage expected

at the telecommunication network connection point of the equipment, arising from external

transients on the network NOTE The effect of transients from cable distribution systems is not taken into account.

mains transient voltage [IEC 60950-1]: highest peak voltage expected at the power input to the

equipment, arising from external transients on the mains supply

mains transient voltage [IEC 62368-1]: highest peak voltage expected at the mains input to the

equipment arising from external transients

protective current rating [IEC 62368-1]: current rating of an overcurrent protective device that

is in the building installation or in the equipment to protect a circuit


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rated current [IEC 62368-1]: input current of the equipment as declared by the manufacturer at

normal operating conditions

required withstand voltage [IEC 62368-1]: peak voltage that the insulation under

consideration is required to withstand

2.9 Remote

remote power feeding [IEC 60065]: supply of power to apparatus via a cable network, for

example a telecommunication network or a cable distribution network for antenna signals

RFT circuit [IEC 60950-21]: remote feeding telecommunication circuit [IEC 60950-21]: a

secondary circuit within the equipment, intended to supply or receive d.c. power via a

telecommunication network at voltages exceeding the limits for tnv circuits, and on which

overvoltages from telecommunication networks are possible

RFT-C circuit [IEC 60950-21]: an rft circuit which is so designed and protected that under

normal operating conditions and single fault conditions, the currents in the circuit do not exceed

defined values NOTE The limit values of current under normal operating and single fault conditions are specified in 6.1

RFT-V circuit [IEC 60950-21]: an rft circuit which is so designed and protected that under

normal operating conditions and single fault conditions, the voltages are limited and the

accessible area of contact is limited NOTE The limit values of voltage under normal operating and single fault conditions are specified in 6.2

RFT circuit, remote feeding (tele)communication circuit [Draft - IEC 62368-3]: circuit

within the equipment not connected to an a.c. mains, intended to supply or receive d.c. power via

an ICT network at voltages exceeding the limits of ES2, and on which overvoltages from ICT

networks are possible NOTE1 to entry: Communication signalling is not required to be present on an RFT circuit.

RFT-C circuit [Draft -IEC 62368-3]: RFT circuit which is so designed and protected that under

normal operating conditions and single fault conditions, the currents in the circuit do not exceed

defined values NOTE 1 to entry: The limit values of current under normal operating conditions and single fault

conditions are specified in 6.3.1.1.

RFT-V circuit [Draft - IEC 62368-3]: RFT circuit which is so designed and protected that

under normal operating conditions and single fault conditions, the voltages are limited and the

accessible area of contact is limited NOTE 1 to entry: The limit values of voltage under normal operating conditions and single fault

conditions are specified in 6.3.1.2.

2.10 Network

telecommunication network [IEC 60950-1]: metallically terminated transmission medium

intended for communication between equipment that may be located in separate buildings,

excluding: the mains system for supply, transmission and distribution of electrical power, if used

as a telecommunication transmission medium; cable distribution systems; SELV circuits

connecting units of information technology equipment NOTE 1 The term telecommunication network is defined in terms of its functionality, not its electrical

characteristics. A telecommunication network is not itself defined as being either an SELV circuit or a


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TNV circuit. Only the circuits in the equipment are so classified.

NOTE 2 A telecommunication network may be: publicly or privately owned; subject to transient overvoltages due to atmospheric discharges and faults in power distribution systems; subject to

longitudinal (common mode) voltages induced from nearby power lines or electric traction lines.

NOTE 3 Examples of telecommunication networks are: a public switched telephone network; a public

data network; an Integrated Services Digital Network (ISDN); a private network with electrical interface

characteristics similar to the above.

telecommunication network transient voltage [IEC 60950-1]: highest peak voltage expected

at the telecommunication network connection point of the equipment, arising from external

transients on the network NOTE The effect of transients from cable distribution systems is not taken into account.

information and communication technology (ICT) network [Draft-IEC 62368-3]: metallically terminated transmission medium consisting of two conductors intended for

communication between equipment that may be located in separate buildings, excluding: the

mains system for supply, transmission and distribution of electrical power, if used as a

communication transmission medium; dedicated HBES/BACS networks; external circuits using

ES1 connecting units of audio/video, information and communication technology equipment NOTE 1 to entry: This may include twisted pairs, and may include circuits, which are subjected to

transients as indicated in table 14 of IEC 62368-1 ID1 (assumed to be 1,5kV),

NOTE 2 to entry: An ICT network may be: publicly or privately owned; subject to longitudinal (common

mode) voltages induced from nearby power lines or electric traction lines,

NOTE 3 to entry: Examples of ICT networks are: a public switched telephone network; a public data

network; an Integrated Services Digital Network (ISDN); a private network with electrical interface

characteristics similar to the above.

NOTE 4 to entry: For information about circuit voltages and signals, which may be present, see Annex B

of IEC 62949 (currently at CD stage).

2.11 Touch

hazardous live [IEC 60065]: electrical condition of an object from which a hazardous touch

current (electric shock) could be drawn Note 1 to entry: See 9.1.1.

touch current [IEC 60950-1]: electric current through a human body when it touches one or

more accessible parts NOTE touch current was previously included in the term "leakage current"

prospective touch voltage [IEC 62368-1]: voltage between simultaneously accessible

conductive parts when those conductive parts are not being touched

touch current [IEC 62368-1]: electric current through a human body when body parts touch

two or more accessible parts or one accessible part and earth

2.12 Mains

mains supply [IEC 60950-1]: power distribution system that is either an AC mains supply or a

DC mains supply

mains [IEC 62368-1]: a.c. or d.c. power distribution system (external to the equipment) that

supplies operating power to the equipment and is PS3


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Note 1 to entry: Mains include public or private utilities and, unless otherwise specified in this standard,

equivalent sources such as motor-driven generators and uninterruptible power supplies.

3 IEC 62368-1 Energy Sources

Most of the IEC 62368-1 energy sources are not defined in the standard terms and definitions

clause. Instead they are defined in the body text, which makes it difficult to gain a rapid

understanding of a particular energy source. This clause contains summary definitions of the

body text. These are for guidance only and are not “official” IEC 62368-1 definitions.

3.1 Abbreviations

3.2 ES (Energy source)

electrical energy source (ES) [Summary]: capacitive source with defined capacitance and

charge voltage or prospective touch voltage and the touch current source with defined values for

normal operation, abnormal operation, and single fault conditions or a pulsed source with

defined values of voltage, current and pulse duration. NOTE – [IEC 62368-1] does not have a formal term and definition entry for ES. This definition is a

summary of [IEC 62368-1] clause 5.2.

ES Electrical energy source PS Power source

ES1 Electrical energy source class 1 PS1 Power source class 1



MS Mechanical energy source RS Radiation energy source

MS1 Mechanical energy source class 1 RS1 Radiation energy source class 1



PIS Potential ignition source TS Thermal energy source

arcing PIS arcing Potential ignition source TS1 Thermal energy source class 1

resistive PIS resistive Potential ignition source TS2 Thermal energy source class 2

TS3 Thermal energy source class 3


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electrical energy source class 1, ES1 [Summary]: class 1 energy source with levels not

exceeding ES1 limits under normal operating conditions, abnormal operating conditions, single

fault conditions of a component, device or insulation not serving as a safeguard and not

exceeding ES2 limits under single fault conditions of a basic safeguard. NOTE 1 – [IEC 62368-1] does not have a formal term and definition entry for ES1. This definition is a


NOTE 2 – ES1 may be accessible to an ordinary person, user, instructed person, service person or a

skilled person. ES1 effects are; not painful on the body, but may be detectable and ignition of combustible

materials not likely.

NOTE 3 – ES1 parameter values are given in [IEC 62368-1] clause 5.2.

electrical energy source class 2, ES2 [Summary]: class 2 energy source with levels not

exceeding ES2 limits under normal operating conditions, abnormal operating conditions, and

single fault conditions, but exceeding ES1 limits. NOTE 1 – [IEC 62368-1] does not have a formal term and definition entry for ES2. This definition is a


NOTE 2 – ES2 may be accessible to an instructed person, service person or a skilled person. ES2 effects

are; painful on the body, but not an injury Ignition of combustible materials possible, but limited growth

and spread of fire

NOTE 3 – ES2 parameter values are given in [IEC 62368-1] clause 5.2

electrical energy source class 3, ES3 [Summary]: class 3 energy source with one or more

parameters exceeding ES2 limits NOTE 1 – [IEC 62368-1] does not have a formal term and definition entry for ES3. This definition is a


NOTE 2 – ES3 may be accessible to a service person or a skilled person. ES3 effects are; injury to the

body and ignition of combustible materials likely with rapid growth and spread of fire.

NOTE 3 – ES3 parameter values are given in [IEC 62368-1] clause 5.2

3.3 PS (Power source)

electrical power source (PS) [Summary]: power source classed by the maximum delivered

power values for a power source operating with a worse-case load and for a power source fault

operating with the specified normal load NOTE 1 – [IEC 62368-1] does not have a formal term and definition entry for PS. This definition is a


electrical power source class 1 (PS1) [Summary]: circuit where the power source does not

exceed a defined limit values measured at specific times. NOTE 1 – [IEC 62368-1] does not have a formal term and definition entry for PS1. This definition is a


NOTE 2 – The power available from external circuits described in Table 14, ID numbers 1 and 2, are

considered to be PS1.

NOTE 3 – Clause 6.2 values are 500 W <3 s and 15 W >3 s.

electrical power source class 2 (PS2) [Summary]: circuit where the power source exceeds PS1

limits; and does not exceed a defined limit value measured after a specified time. NOTE 1 – [IEC 62368-1] does not have a formal term and definition entry for PS2. This definition is a


NOTE 2 – Clause 6.2 values are 100 W >5 s.


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electrical power source class 3 (PS3) [Summary]: circuit whose power source exceeds PS2

limits, or any circuit whose power source has not been classified. NOTE 1 – [IEC 62368-1] does not have a formal term and definition entry for PS2. This definition is a


3.4 PIS (Potential ignition source)

potential ignition source (PIS) [IEC 62368-1]: location where electrical energy can cause

ignition

arcing PIS [IEC 62368-1]: circuit where the power source does not exceed a defined limit

values measured at specific times. location where an arc may occur due to the opening of a

conductor or a contact NOTE 1 An electronic protection circuit or additional constructional measures may be used to prevent a

location from becoming an arcing PIS .

NOTE 2 A faulty contact or interruption in an electric connection that may occur in conductive patterns

on printed boards is considered to be within the scope of this definition.

resistive PIS [IEC 62368-1]: location where a component may ignite due to excessive power

dissipation

4 Harmonising Example

The problem with trying to create harmonised IEC 60950 and IEC 62368 definitions for the

telecommunications industry is that IEC 62368 doesn’t acknowledge ELV, SELV and TNV

circuits. Instead one has to define the equivalent (ES) voltage and (PS) power level of those

circuits together with any overvoltages that occur.

IEC 62368 doesn’t acknowledge telecommunications either preferring to use Information and

Communications Technology (ICT). In places IEC 62368 reduces a network to just the wiring.

4.1 Existing definitions in standards

RFT circuit [IEC 60950-21]: remote feeding telecommunication circuit [IEC 60950-21]: a

secondary circuit within the equipment, intended to supply or receive d.c. power via a

telecommunication network at voltages exceeding the limits for tnv circuits, and on which

overvoltages from telecommunication networks are possible

RFT circuit, remote feeding (tele)communication circuit [Draft - IEC 62368-3]: circuit

within the equipment not connected to an a.c. mains, intended to supply or receive d.c. power via

an ICT network at voltages exceeding the limits of ES2, and on which overvoltages from ICT

networks are possible NOTE 1 to entry: Communication signalling is not required to be present on an RFT circuit.

RFT circuit [K.50]: A circuit, other than SELV or TNV circuit, intended for the supply of

power to equipment via a paired-conductor network, and which is so designed and protected that

under normal operating and single fault conditions the voltages or currents do not exceed defined

values. The circuit in the equipment that receives power from an RFT circuit is also considered

to be an RFT circuit.


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4.2 Harmonised definition for the RFT circuit term

The main aims of the definition are to:

1 Incorporate both IEC 60950-1 terms (SELV and TNV) and IEC 62368-1 terms (ES and

PS) to create a forward looking and backwards compatible definition

2 Capture operational conditions of IEC 60950-1 (normal operating and single fault

conditions) and IEC 62368-1 (normal operating conditions, abnormal operating

conditions, and single fault conditions)

3 Set the voltage range to cover ES2 and ES3 circuit (60 V and greater)

4 Comprehended US practices for RFT circuits

RFT circuit (remote feeding telecommunication circuit): equipment circuit, without a direct

mains connection or being a SELV circuit or a TNV service or a limited current circuit or an ES1

PS1 circuit, intended to supply or receive d.c. power, at voltages, currents and powers that do not

exceed defined values under specified operational conditions when connected to paired-

conductor communications network on which overvoltages are possible NOTE 1: A telecommunications service is not required to be present on an RFT circuit.

NOTE 2: Specified conditions include normal operating and single fault conditions and may include

abnormal operating and safeguard failure conditions.

By themselves the ELV, SELV and TNV circuits are only defined in terms of voltage. IEC

60950-1 does define that the normal telecommunication service is limited to 15 W, which is

equivalent to the IEC 62368-1 PS1 power level.

A compiled definition of hazardous voltage secondary circuit is useful

hazardous voltage secondary circuit: secondary circuit operating at a voltage exceeding 42,4 V

peak, or 60 V d.c., existing in a circuit that does not meet the requirements for either a limited

current circuit or a TNV circuit. NOTE 1 – Definition is derived from [IEC 60950-1] terms secondary circuit and hazardous voltage.

NOTE 2 – The term combination hazardous voltage secondary circuit is used in [IEC 60950-1] but not

defined.

The RFT circuit definition given means an it is a hazardous voltage circuit (>60 V d.c. or >ES1

source voltage) capable of delivering powers in excess of 15 W (>PS1).


15

Appendix I

IEC 60950-1 voltages

Introduction

In the body of the standard defines the voltage limits for the various circuits.

Parameters

In an SELV circuit the voltages between any two conductors of the SELV circuit or circuits and

between any one such conductor and earth shall not exceed 42.4 V rms maximum, or 60 V d.c..

Under a single fault condition and for periods of less than 200 ms the voltage shall not exceed 71

V rms maximum or 120 V d.c..

In a telecommunication network the transient overvoltage is assumed to be 1.5 kV peak in TNV-

1 circuit and a TNV-3 circuit. IEC 60950 in clause G.3 specifies an 800 V peak transient

overvoltage for an SELV circuit and a TNV-2 circuit if they are connected to a

telecommunication network, yet the SELV and TNV-2 definitions say they are not subject to

overvoltages!

From the conditions and values provided Table I.1 can be made to summarize the environments.

Table I.1 IEC 60950-1 voltage environments

Condition Circuit powering voltage environment

SELV TNV-1 TNV-2 TNV-3 Hazardous

d.c. supply voltage (V) < 60 < 60 > 60

< 120

> 60

< 120

> 60

Single fault supply

voltage < 0.2 s (V)

< 120 < 1500 for < 1 ms

< 400 after 14 ms

see NOTE 1

< 1500 for < 1 ms

< 400 after 14 ms

see NOTE 1

< 1500 for < 1 ms

< 400 after 14 ms

see NOTE 1

As

applicable

Telecommunications

overvoltage (V)

NA

see NOTE 2

Yes

1500, 10/700

impulse

NA

see NOTE 2

Yes

1500, 10/700

impulse

As

applicable

NOTE 1: See IEC 60950-1 Figure 2F for other voltage-time values.

NOTE 2: IEC 60950-1 clause G.3 states an 800 V peak transient overvoltage for an SELV circuit and a TNV-2 circuit if they are connected to a

telecommunication network.


16

Appendix II

IEC 62368-1 electrical source parameters

Introduction

Compared to a voltage source an energy source has additional attributes and some parameters

may have a range of values e.g. capacitance value with voltage in a given class. To fully

understand the energy source class requirements clause 5, Electrically-caused injury, must be

read.

Power sources, which can be loads or sources, are classified by their steady state power after a

defined time period. There is no power limitation defined for the initial start-up time of 3 s to 5 s.

Parameters

From the clause 5 conditions and values Table II.1 summarizes spot parameter values for

comparison with Table I.1. For ES1 and ES2 energy sources all the parameters must conform to

the class requirements. An ES3 energy source has one or more parameters that exceed ES2 limit

values. Table I.1 does not included pulsed ES parameters.

Table II.1 IEC 62368-1 energy source parameters

Condition Energy source parameters

ES1 ES2 ES3

Steady state (> 2 s) d.c. supply touch voltage (V)

see NOTE 1

< 60 < 120 > 120

Single fault supply touch voltage 0.2 s to 2 s (V) < 60

see NOTE 5

< 120 > 120

Single fault supply touch voltage for < 0.2 s (V) < 60

see NOTE 5

< 198 for < 10 ms

< 150 for < 50 ms

see NOTE 2

> 198 for < 10 ms

> 150 for < 50 ms

see NOTE 2

DC touch current (mA) < 2 < 25 > 25

Single fault supply touch current 0.2 s (mA) < 2

see NOTE 6

<62 > 62

Single fault supply touch current for < 0.2 s (mA) < 2

see NOTE 6

< 200 for < 10 ms

< 107 for < 50 ms

see NOTE 7

> 200 for < 10 ms

> 107 for < 50 ms

see NOTE 7

Capacitance of charged capacitor (nF)

See NOTE 3

300 or greater 300 or greater > 300 or greater

External paired conductor circuit overvoltage (V)

See NOTE 4

1500,

10/700 impulse

1500,

10/700 impulse

> 1500,

10/700 impulse

NOTE 1 Applies to normal operating conditions, abnormal operating conditions, and single fault conditions for periods greater than 2 s.

NOTE 2 Other time values of voltage are given in IEC 62368-1 Table 6

NOTE 3 Value given is for the steady state supply voltage. Other capacitance values for different voltages are given in IEC 62368-1 Table 5

NOTE 4 Only differential if one conductor is earthed in the equipment.

NOTE 5 ES1 values from IEC 62368 Table 6 quoted. However, under single fault conditions of a basic safeguard the single fault ES2 limits apply.

NOTE 6 ES1 values from IEC 62368 Table 7 quoted. However, under single fault conditions of a basic safeguard the single fault ES2 limits

apply. NOTE 7 Other time values of current are given in IEC 62368-1 Table 7


17

Power source classifications and measurements are described in the 6.2.2 Power source circuit

classifications clause. Table II.2 reports the levels defined in clause 6.2.2.

Capacitance limits: When the ES is capacitor, the energy source is classified by the maximum

charge voltage for a given capacitance value. This leads to voltages that are above the limit

voltage for a voltage-current ES. From Table 5 – Electrical energy source limits for a charged

capacitor (ES) the three following graphs of capacitance, charge and energy can be created.

For ES1 the capacitor values, in µF, for voltages above 500 V is given by 4/VES, where VES is

the value of charge voltage. Similarly, for ES2 the capacitor values, in µF, for voltages above

1000 V is given by 8/VES.

Capacitive ES Charge Voltage - V

10 100 1000 10000

Cap

acitiv

e E

S m

axim

um

cap

acita

nce v

alu

e -

nF

0.1

1

10

100

1000

ES1

ES2


10 100 1000 10000

Ca

pa

citiv

e E

S m

axim

um

ch

arg

e v

alu

e -

µC

3

4

5

6

7

89

20

30

40

10

ES1

ES2


18

Table II.2 IEC 62368-1 power source parameters

Condition Power source parameters

PS1 PS2 PS3

Maximum steady state power (W)

see NOTE

15, >3 s 100, >5 s > 100

Short term power (W) Undefinied, < 3 s

see NOTE 5

Undefined, < 5 s Undefined

NOTE The electrical power source classification shall be determined by measuring the maximum power under each of the following conditions:

– for load circuits: a power source under normal operating conditions as specified by the manufacturer into a worst-case fault (see 6.2.2.2);

– for power source circuits: a worst-case power source fault into the specified normal load circuit (see 6.2.2.3).


10 100 1000 10000

Ca

pa

citiv

e E

S m

axim

um

sto

red

en

erg

y -

mJ

0.1

1

10

ES1

ES2


19

Appendix III

Safety equivalence of IEC 60950-1 and IEC 62368-1

Introduction

This data is from IEC 62368-1 Annex W (informative) Comparison of terms introduced in this

standard. People miss the important Annex statement of “The (sic electrical energy source)

electrical characteristics are not identical to TNV circuits but will give equivalent level of

safety”. Thus it is wrong to say a circuit containing an ES2 on which transients occur is

equivalent to a TNV-3 circuit. But one can say that the same safety rules apply.

Safety equivalence

From a safety perspective the following approximations can be made according to IEC 62368-1

Annex W.

Table III.1 Safety equivalence of IEC 60950-1 and IEC 62368-1

IEC 60950-1 IEC 62368-1

SELV ES1

TNV-1 ES1

External circuits have impulse testing see NOTES 1 through 3

TNV-2 ES2

TNV-3 ES2

External circuits have impulse testing see NOTES 1 through 3

NOTE 1 Paired conductor (shielded or unshielded) - tested with1500 V, 10/700.

Only differential if one conductor is earthed in the equipment NOTE 2 Any other conductors – tested with mains transient or known external circuit overvoltage impulse

whichever is higher. The external circuit is not earthed at either end, but there is an earth reference

NOTE 3 Cable distribution network coaxial cable – tested with 4000 V, 10/700 centre conductor to shield cable (shield is earthed at the equipment).

Not applicable to power-fed coaxial repeaters.

iec 60950 and iec 62368 safety standard terminology€¦ · as for operator access areas, except as...

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