1

Table of Contents

Introduction ..............................................................................2

Distribution Systems ...............................................................4

Panelboards..............................................................................6

Overcurrent Protective Devices ............................................11

Panelboard Construction .......................................................16

Types Of Panelboards ............................................................25

Individual Overcurrent Protection.........................................30

Power Supply Systems..........................................................35

Service Entrance Panelboards ..............................................38

Panelboard Grounding ..........................................................41

Ground Fault Protection ........................................................46

Panelboard Ratings ................................................................48

S1, S2, And SE Lighting Panelboards ...................................52

Transient Protection System (TPS) .......................................57

S4 And S5 Power Panelboards .............................................61

F1 And F2 Fusible Panelboards .............................................63

Telephone And Equipment Panelboards ..............................68

Seismic Rated Panelboards ...................................................69

Accessories ............................................................................70

Catalog Numbers ...................................................................73

Information Needed To Order Panelboards..........................76

Review Answers ....................................................................78

Final Exam ..............................................................................79

2

Introduction

Welcome to another course in the STEP 2000 series,Siemens Technical Education Program, designed to prepareour distributors to sell Siemens Energy & Automation prod-ucts more effectively. This course covers Panelboards andrelated products.

Upon completion of Panelboards you will be able to:

� Explain the role of panelboards in a distribution system

� Define a panelboard according to the National ElectricalCode

� Distinguish between a lighting and appliancepanelboard versus a power and distribution panelboard

� Explain the need for circuit protection

� Identify various components of a Siemens panelboard

� Distinguish between a main breaker and main lug onlypanelboard

� Identify various power supply systems

� Explain the use of panelboards used as service-entranceequipment

� Describe the proper grounding techniques of serviceentrance and downstream panelboards

� Identify various ratings of Siemens panelboards

� Identify panelboard accessories

3

This knowledge will help you better understand customerapplications. In addition, you will be able to describe productsto customers and determine important differences betweenproducts. You should complete Basics of Electricity andMolded Case Circuit Breakers before attemptingPanelboards. An understanding of many of the conceptscovered in Basics of Electricity and Molded Case CircuitBreakers is required for Panelboards.

If you are an employee of a Siemens Energy & Automationauthorized distributor, fill out the final exam tear-out card andmail in the card. We will mail you a certificate of completion ifyou score a passing grade. Good luck with your efforts.

I-T-E, Vacu-Break and Clampmatic are registered trademarksof Siemens Energy & Automation, Inc.

Sentron is a trademark of Siemens Energy & Automation, Inc.

National Electrical Code and NEC are registered trademarks ofthe National Fire Protection Association, Quincy, MA 02269.Portions of the National Electrical Code are reprinted withpermission from NFPA 70-1996, National Electrical CodeCopyright, 1995, National Fire Protection Association, Quincy,MA 02269. This reprinted material is not the complete andofficial position of the National Fire Protection Association onthe referenced subject which is represented by the standardin its entirety.

Underwriters Laboratories Inc. is a registered trademark ofUnderwriters Laboratories Inc., Northbrook, IL 60062. Theabbreviation �UL� shall be understood to mean UnderwritersLaboratories Inc.

Other trademarks are the property of their respective owners.

4

Distribution Systems

A distribution system is a system that distributes electricalpower throughout a building. Distribution systems are usedin every residential, commercial, and industrial building.

Most of us are familiar with the distribution system found inthe average home. Power, purchased from a utility companyenters the house through a metering device. The power isthen distributed from a load center to various branch circuitsfor lighting, appliances, and electrical outlets.

Meter

Load Center

Utility Power

Main ServiceDisconnect

Branch Breakers

Residential distribution

5

Distribution systems used in multifamily, commercial, andindustrial locations are more complex. A distribution systemconsists of metering devices to measure power consumption,main and branch disconnects, protective devices, switchingdevices to start and stop power flow, conductors, and trans-formers. Power may be distributed through various switch-boards, transformers, and panelboards. Good distributionsystems don�t just happen. Careful engineering is required sothat the distribution system safely and efficiently suppliesadequate electric service to both present and possible futureloads.

Building

Outside Switchgear

Transformer

Disconnect

Switchboard

PowerPanelboard

LightingPanelboard

MotorControl

Utility Power

Industrial distribution

6

Panelboards

Electrical distribution systems, whether simple or complex,typically include panelboards, the focus of this course.Panelboards provide circuit control and overcurrentprotection.

The National Electrical Code® (NEC®) defines a panelboardas a single panel or group of panel units designed for assem-bly in the form of a single panel; including buses, automaticovercurrent devices, and equipped with or without switchesfor the control of light, heat, or power circuits; designed tobe placed in a cabinet or cutout box placed in or against awall or partition and accessible only from the front(Article 100-definitions).

NEC® and National Electrical Code® are registered trademarks of the National Fire

Protection Association.

Panelboard definition

7

According to the NEC definition, panelboards are:

� Used to control light, heat, or power circuits

� Placed in a cabinet or cutout box

� Mounted in or on a wall

� Accessible only from the front

Placed In CabinetOr Cutout Box

Mounted OnOr In A Wall

Accessible OnlyFrom The Front

Used To ControlLight, Heat, OrPower Circuits

Note: Article 384 in the National Electrical Code coverspanelboards. The basic requirements for panelboardsare given in NEC Sections 384-13 through 384-16. Youare encouraged to become familiar with this material.

Panelboards basically fall into two categories:

� Lighting and appliance

� Power and distribution

8

Article 384-14 and 384-15 of the National Electrical Codegives three primary requirements for lighting and appliancepanelboards. In order for a panelboard to be a lighting andappliance panelboard, according to NEC 384-14, the follow-ing conditions must be met:

1. More than 10% of the overcurrent devices (poles) mustbe rated 30 amps or less.

2. A neutral connection must be provided.

Once a panelboard has met the two previous conditionsrequired of a lighting and appliance panelboard, then a thirdcondition exists in NEC 384-15.

3. A maximum of 42 overcurrent devices (poles) areallowed in any one cabinet or enclosure.

A neutral is a current-carrying component that is connectedto the third wire of a single-phase, three wire system orthe fourth wire of a three-phase, four wire system. Forexample, the following illustration shows the secondary ofa 480 volt, wye-connected, three-phase transformer. Thereis 480 volts between phases and 277 volts betweenany phase and neutral (N).

480 volts

A

B

N

C

480 volts

480 volts

277 volts

277 volts

277 volts

Lighting and appliancepanelboards

Neutral connection

9

Each pole of a circuit breaker is considered one overcurrentdevice. For example, a 1-pole breaker is one overcurrentdevice and a 2-pole breaker is two overcurrent devices. Amaximum of 42 overcurrent devices are allowed in a lightingand appliance panelboard.

2-Pole Circuit BreakerTwo Overcurrent Devices

1-Pole Circuit BreakerOne Overcurrent Device

In the following example, a three-phase, four-wire (the fourthwire is neutral) distribution system is used to supply apanelboard. The panelboard has five 1-pole, 15 A breakers;twenty-one 1-pole, 20 A breakers; and eight 2-pole, 40 Abreakers for a total of 42 overcurrent devices. Ten percent ormore of these overcurrent devices must be rated for 30 ampsor less. In this example five overcurrent devices are required(10% of 42 = 4.2). There are 26 overcurrent devices rated at30 amps or less. This is a lighting and appliance panelboard.

Number OfCircuit Breakers

Description Number OfOvercurrent Devices

521

8

1-Pole, 15 A1-Pole, 20 A2-Pole, 40A

5211642

Overcurrent devices

More than 10% of theovercurrent devices arerated 30 amps or less

10

NEC defines power and distribution panelboards as allpanelboards that are not lighting and appliance. In thefollowing example there are only four overcurrent deviceswhich are rated at 30 amps or less. This panelboard doesnot qualify as a lighting and appliance panelboard. It is apower and distribution panelboard.

Number OfCircuit Breakers

Description Number OfOvercurrent Devices

422

8

1-Pole, 30 A1-Pole, 40 A2-Pole, 40A

4221642

1. A ____________ ____________ distributes electricalpower throughout a building.

2. Which of the following does not meet the NEC defini-tion for a panelboard?

a. controls light, heat, or power circuitb. accessible from the front or backc. mounted in or on a walld. placed in a cabinet or cutout box

3. Article ____________ in the National Electrical Codecovers panelboards.

4. The following is an example of a ____________ and____________ panelboard.

Number OfCircuit Breakers

Description Number OfOvercurrent Devices

244

3-Pole, 60 A2-Pole, 30 A1-Pole, 15 A

684

18

Why? ________________________________________

Power and distributionpanelboards

Review 1

11

Overcurrent Protective Devices

Excessive current is referred to as overcurrent. The NationalElectrical Code defines overcurrent as any current in excessof the rated current of equipment or the ampacity of a con-ductor. It may result from overload, short circuit, or groundfault (Article 100-definitions).

Current flow in a conductor always generates heat. Thegreater the current flow, the hotter the conductor. Excessheat is damaging to electrical components. For that reason,conductors have a rated continuous current carrying capacityor ampacity. Overcurrent protection devices are used toprotect conductors from excessive current flow. These pro-tective devices are designed to keep the flow of current in acircuit at a safe level to prevent the circuit conductors fromoverheating.

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Circuit protection would be unnecessary if overloads andshort circuits could be eliminated. Unfortunately, overloadsand short circuits do occur. To protect a circuit against thesecurrents, a protective device must determine when a faultcondition develops and automatically disconnect the electri-cal equipment from the voltage source. An overcurrent pro-tection device must be able to recognize the difference be-tween overcurrents and short circuits and respond in theproper way. Slight overcurrents can be allowed to continuefor some period of time, but as the current magnitude in-creases, the protection device must open faster. Short cir-cuits must be interrupted instantly.

A fusible disconnect switch is one type of device used onpanelboards to provide overcurrent protection. Properlysized fuses located in the switch open when an overcurrentcondition exists.

A fuse is a one-shot device. The heat produced byovercurrent causes the current carrying element to meltopen, disconnecting the load from the source voltage.

Good Element

Open Element

Fusible disconnect switch

Fuse

13

Nontime-delay fuses provide excellent short circuit protec-tion. When an overcurrent occurs, heat builds up rapidly inthe fuse. Nontime-delay fuses usually hold 500% of theirrating for approximately one-fourth second, after which thecurrent-carrying element melts. This means that these fusescannot be used in motor circuits which often have inrushcurrents greater than 500%.

Time-delay fuses provide overload and short circuitprotection. Time-delay fuses usually allow five times the ratedcurrent for up to ten seconds to allow motors to start.

Fuses are grouped into classes based on their operating andconstruction characteristics. Each class has an ampereinterrupting capacity (AIC) which is the amount of faultcurrent they are capable of interrupting without destroyingthe fuse casing. Fuses are also rated according to themaximum continuous current and maximum voltage they canhandle. Underwriters Laboratories (UL) establishes and stan-dardizes basic performance and physical specifications todevelop its safety test procedures. These standards haveresulted in distinct classes of low voltage fuses rated at 600volts or less. The following chart lists the fuse class and itsAIC rating.

HKRJL

10,000 A50,000 A

200,000 A200,000 A200,000 A

AIC RatingClass

An optional Class R fuseholder can be used to prevent anyother type of fuse from being used. The Class R rejection clipcontains a pin that permits only the notched Class R fuse tobe inserted. This prevents a lower rated fuse from beingused.

Pin

Notch

Rejection Clip

Nontime-delay fuses

Time-delay fuses

Fuse classes

Class R fuseholder

14

Another device used for overcurrent protection is a circuitbreaker. The National Electrical Code defines a circuit breakeras a device designed to open and close a circuit by nonauto-matic means, and to open the circuit automatically on apredetermined overcurrent without damage to itself whenproperly applied within its rating.

Circuit breakers provide a manual means of energizing anddeenergizing a circuit. In addition, circuit breakers provideautomatic overcurrent protection of a circuit. A circuitbreaker allows a circuit to be reactivated quickly after a shortcircuit or overload is cleared. Unlike fuses which must bereplaced when they open, a simple flip of the breaker�shandle restores the circuit.

Like fuses, every circuit breaker has a specific ampere, volt-age, and fault current interruption rating. The ampere ratingis the maximum continuous current a circuit breaker cancarry without exceeding its rating. As a general rule, thecircuit breaker ampere rating should match the conductorampere rating. For example, if the conductor is rated for20 amps, the circuit breaker should be rated for 20 amps.Siemens I-T-E® breakers are rated on the basis of using60° C or 75° C conductors. This means that even if a conduc-tor with a higher temperature rating were used, the ampacityof the conductor must be figured on its 60° C or 75° C rating.

Circuit breakers

Ampere rating

15

There are some specific circumstances when the ampererating is permitted to be greater than the current carryingcapacity of the circuit. For example, motor and welder circuitscan exceed conductor ampacity to allow for inrush currentsand duty cycles within limits established by NEC.Generally the ampere rating of a circuit breaker is selected at125% of the continuous load current. This usually corre-sponds to the conductor ampacity which is also selected at125% of continuous load current. For example, a 125 ampcircuit breaker would be selected for a load of 100 amps.

The voltage rating of the circuit breaker must be at least equalto the circuit voltage. The voltage rating of a circuit breakercan be higher than the circuit voltage, but never lower. Forexample, a 480 VAC circuit breaker could be used on a 240VAC circuit. A 240 VAC circuit breaker could not be used on a480 VAC circuit. The voltage rating is a function of the circuitbreakers ability to suppress the internal arc that occurs whenthe circuit breaker�s contacts open.

Circuit breakers are also rated according to the level of faultcurrent they can interrupt. When applying a circuit breaker,one must be selected which can sustain the largest potentialshort circuit current which can occur in the selected applica-tion. Siemens circuit breakers have interrupting ratings from10,000 to 200,000 amps. To find the interrupting rating of aspecific circuit breaker refer to the Speedfax catalog.

Voltage rating

Fault currentinterruption rating

16

The can

Panelboard Construction

There are several components that make up a panelboard.Panelboards contain a can, interior, circuit protectiondevices, label, and trim.

The can is typically constructed of galvanized steel andhouses the other components. The can is also referred to asthe box or an enclosure. It is designed to provide compo-nent and personnel protection. Removable blank end panelsallow the user to cut whatever conduit holes are necessary.Prestamped knockouts are available as an option. Mountingstuds are used to support the interior or group mounteddevices.

Can

RemovableEnd Panel

Mounting Stud

17

Interior

Cans Ahead Siemens has a �Cans Ahead� program in which the can ofsome panelboards can be shipped separately of the interiorand trim. This allows the contractor to install the can firstbefore the wall is finished. For information on this programcontact your Siemens sales representative.

The interior consists of several components, includingovercurrent protection devices, bus bars and insulatedneutral bus bars. The interior is mounted to the fourmounting studs in the can. Jacking screws (not shown) allowadjustment of the interior within the enclosure.

18

Bus bars A bus bar is a conductor that serves as a commonconnection for two or more circuits. It is representedschematically by a straight line with a number of connectionsmade to it. NEC article 384-3 states that bus bars shall belocated to be free from physical damage and shall be heldfirmly in place. Standard bus bars on Siemens panelboardsare made of aluminum, but copper bus bars are available asan option.

Bus Bar

Branch Circuits

Bus bars are required to have phases in sequence so that aninstaller can have the same fixed phase arrangement in eachtermination point in any panelboard or switchboard. This isestablished by NEMA (National Electrical ManufacturersAssociation). It is possible to have a non-NEMA phasesequence which would have to be marked on thepanelboard. It is assumed that bus bars are arrangedaccording to NEMA. The following diagram illustratesaccepted NEMA phase arrangements.

A

C

B

B

C

A

Vertical Horizontal

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An insulated neutral bus is provided. In many instances it is asplit neutral, meaning that an equal number of neutral con-nections are available on both sides of the panelboard. Splitneutrals are connected together through a bus bar. An insula-tion separates the neutral bus from the power supply busbars.

Some loads can cause harmonics and non-linear loading on adistribution system. This requires special consideration whenordering a panelboard. One way to deal with non-linear loadsis to double the capacity of the panelboard neutral. A 200%neutral can be factory installed or, in the case of the S1, S2and SE, field installed.

Circuit protection devices mount directly to the bus bars. Inthe following illustration for example, a BL circuit breaker ismounted to the panelboard bus.

BL Type Circuit Breaker

Bus Bars

Split neutral

200% neutral

Circuit protection devices

20

Circuits must be clearly labeled. Poles arranged with oddnumbers on the panelboard�s right (your left) and even num-bers on the panelboard�s left (your right) is referred to asNEMA numbering. In some areas a vertical sequence isrequired. In addition a directory card is placed in a holderwhich is attached to the inside of the door.

1

3

5

7

9

11

13

15

24

6

8

10

12

14

16

1817

1

2

3

4

5

6

7

8

1011

12

13

14

15

16

17

189

NEMA Numbering Vertical Numbering

The label identifies the panelboard�s type, voltage rating, andampacity.

Circuit identification

Label

21

The dead front and trim are the front surfaces of thepanelboard that cover the interior. The trim includes anaccess door. These components provide access to theovercurrent devices while sealing off the bus bars andinternal wiring from contact.

Trim

Access Door

Part of the dead front are the QF3 filler plates. These are usedto cover any unused pole spaces not filled by a circuitbreaker.

QF3 Filler Plate

Circuit Breaker

Dead front and trim

QF3 filler plates

Dead Front

22

The National Electrical Manufacturers Association (NEMA)has established guidelines for electrical equipment enclo-sures. Siemens panelboards are supplied as standard in aNEMA Type 1 enclosure which is intended for generalpurpose indoor use.

The following enclosures are available as an option:

Type 3R Enclosures are intended for outdoor use prima-rily to provide a degree of protection againstrain, sleet and damage from external iceformation.

Type 4X Enclosures are intended for indoor or outdooruse primarily to provide a degree of protectionagainst corrosion, windblown dust and rain,splashing water, hose-directed water, and dam-age from external ice formation.

Type 3R/12 Enclosures are intended for indoor use primarilyto provide a degree of protection against circu-lating dust, falling dirt, and dripping noncorro-sive liquids.

Enclosures

23

Panelboard installation Additional information concerning NEMA enclosures can befound in NEMA publication 250-1991, Enclosures for ElectricalEquipment (1000 Volts Maximum). Article 110-16 of theNational Electrical Code specifies clearances aroundpanelboards which will provide sufficient access and workingspace. You should become familiar with this material. Thereare three basic rules which we must be concerned with:

� Minimum distance from the panelboard to ground shallbe 3 feet for 0-150 volt systems and 4 feet for 151-600volt systems.

� Space in front of the equipment shall be at least 30inches wide and be sufficient to allow the hinged door toopen 90 degrees.

� There shall be a minimum of 6 ½ feet of headroom.

24

Review 21. A ____________ is a conductor that serves as a

common connection for two or more circuits.

2. Circuit protection devices are designed to keep theflow of ____________ in a circuit at a safe level toprevent the circuit conductors from overheating.

3. Three causes of overcurrent are:

a. ____________

b. ____________

c. ____________

4. A Class K fuse has an ampere interrupting capacity of____________ amps.

5. A Class ____________ fuse has a notch to fit a rejec-tion clip.

6. Circuit breakers are rated for continuous____________ , ______________, and fault currentinterruption capacity.

7. The panelboard components designed to seal off thebus bars and internal wiring from contact are the____________ and ____________ .

8. Siemens panelboards are supplied standard in aNEMA Type ____________ enclosure.

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Types Of Panelboards

There are two types of panelboards, main breaker and mainlug only.

The incoming supply cables of a main breaker typepanelboard are connected to the line side of the mainbreaker, which in turn feeds power to the panelboard and itsbranch circuits. The main breaker disconnects power fromthe panelboard and protects the system from short circuits,overloads and ground faults if equipped with ground faultprotection. Siemens main breakers are bus connected to themain bus bars. This means there are no cable connectionsrequired from the main circuit breaker to the lugs on themain bus bars. Bus connecting provides a higher degree ofcircuit integrity because there is less chance for loose con-nections which lead to overheating.

Bus Connected

Main breaker typepanelboard

26

Depending on the panelboard the main breaker can either bemounted horizontally or vertically.

MainBreaker

BranchBreaker

BranchBreaker

MainBreaker

Supply SupplyTo BranchCircuit

Main BreakerMounted Horizontally

Main BreakerMounted Vertically

A main lug only type panelboard does not have a main circuitbreaker. The incoming supply cables are connected directly tothe bus bars. Primary overload protection for the panelboardis not provided as an integral part of the panelboard.

Main lug only

27

There are a variety of ways a main breaker or main lug onlypanelboard might be used. For example, a lighting and appli-ance panelboard can have a maximum of 42 poles. If morebranch circuits were required an additional panelboard couldbe used. Feed-through lugs are used to connect a mainbreaker and main lug only panelboard when they aremounted adjacent to each other. A main breaker panelboarduses feed-through lugs mounted on the main bus of thepanelboard and interconnecting cables are routed to themain lug only panelboard. The main breaker protects bothpanelboards from overcurrent.

MainBreaker

Feed-Through Lugs

Supply

Feed-through lugs

28

Sub-feed lugs are used to connect two main lug onlypanelboards that are mounted adjacent to each other. Forexample two main lug only panelboards might be supplied bya circuit breaker or fused disconnect. Power supplied by theovercurrent protection device are routed to the firstpanelboard. The power is routed to the second panelboardthrough sub-feed lugs.

Incoming Feeder Cables

Sub-Feed Lugs

Fused Disconnect SwitchOr Circuit Breaker

Sub-feed lugs

29

Unit space is the area that accommodates the branch circuitbreakers in most power panelboards. In addition, the numberof branch circuits determines the panel dimensions in lightingpanels.

When an application requires a circuit breaker that is a largerframe size than the branch circuit breakers available and willnot fit in the branch circuits location, a subfeed breaker canbe used. One possible application is to supply a secondpanelboard located some distance from the first panelboard.This is, however, not the only application. A subfeed breakercan supply any load that a branch circuit breaker can supply.

MainBreaker

Sub-FeedBreaker

Unit space andsubfeed breakers

30

Individual Overcurrent Protection

The National Electrical Code requires panelboards to beindividually protected against overcurrent. Main overcurrentprotection may be an integral part of a panelboard or locatedremote from the panelboard. NEC Article 384-16 states thateach lighting and appliance branch-circuit panelboard shallbe individually protected on the supply side by not more thantwo main circuit breakers or two sets of fuses having acombined rating not greater than that of the panelboard.

The following illustration shows two possible ways individualpanelboard overcurrent can be accomplished. A main circuitbreaker can be located as an integral part of the panelboardor can be located remotely. In this example the main breakerand panelboard are both rated for 600 amps.

Individual protection

31

Split bus Panelboards can have as many as two main circuit breakersor two sets of fuses to protect. When two main circuitbreakers are used in a panelboard a split bus is used. Half ofthe branch circuits are protected by one main circuit breakerand half protected by the other main circuit breaker.

32

There is an exception to NEC Article 384-16. Exception No. 1:Individual protection for a lighting and appliance panelboardshall not be required if the panelboard feeder hasovercurrent protection not greater than the rating of thepanelboard. The following illustration shows twopanelboards protected by a single 600 Amp fused disconnectswitch. Note that the fused disconnect feeder providesovercurrent protection not greater than the rating of thepanelboards.

Exception to NEC 384-16

33

Panelboards suppliedby a transformer

Frequently a panelboard is supplied by the secondary of atransformer. According to NEC Article 384-16d, individualprotection for the panelboard must be provided on the sec-ondary side of the transformer. The overcurrent protectiondevice can be installed either ahead of or in the panelboard.

Neutral Bus

Transformer

Panelboard

Transformer

Neutral Bus

Panelboard

Overcurrent ProtectionProvided In Panelboard

Overcurrent ProtectionProvided Ahead Of Panelboard

NEC makes an exception to this rule. A panelboard suppliedby a single-phase transformer having a 2-wire (single-voltage)secondary can be protected by an overcurrent protectiondevice located on the primary side of the transformer.

34

1. The two types of panelboards are main ____________and main ____________ only.

2. The main breaker of a main breaker panel can bemounted ____________ or ____________ .

3. Primary overload protection for a main ____________type panelboard is not provided as an integral partof the panelboard.

4. ____________ - ____________ lugs are used to con-nect a main breaker and main lug only panelboardwhen they are mounted adjacent to each other.

5. The NEC article that covers individual overcurrentprotection for panelboards is ____________ .

6. A lighting and appliance panelboard can have asmany as ____________ main circuit breakers or setsof fuses to protect it.

Review 3

35

Power Supply Systems

Panelboards receive power from a variety of sources. Down-stream panelboards may receive power from upstreampanelboards or switchboards, however, power for the distri-bution system originates from a utility power company.Power from the power company is stepped down throughtransformers to be distributed in residential, commercial andindustrial locations. Several systems are used. The followingare some examples of systems in use that are suitable forSiemens panelboards.

The following diagram illustrates one of the most commonsingle-phase, three-wire distribution systems in use today.There are 120 volts between any phase and neutral and 240volts between phases.

N

N

Primary

120 volts

120 volts240 volts

Single-phase, three-wiresystem

36

The following illustration shows the secondary of a480 Y/277 V three-phase, four-wire, wye-connectedtransformer. The �480 Y� indicates the transformer iswye-connected and has 480 volts between any two phases.The �277 V� indicates there are 277 volts between any phaseand neutral (N). Phase-to-phase voltage is 1.732 times phase-to-neutral voltage (277 x 1.732 = 480).

480 volts

480 volts

480 volts

A

B

C

N

277 voltsA - B 480 voltsB - C 480 voltsC - A 480 voltsA - N 277 voltsB - N 277 voltsC - N 277 volts

Three-phase, four-wire,wye-connectedtransformers

37

A three-phase, four-wire, delta-connected secondary works alittle differently. The following illustration shows a delta-connected secondary with 240 volts phase-to-phase. Themidpoint of one phase winding is grounded to provide 120volts between phase A and neutral and 120 volts betweenphase C and neutral. Between phase B and neutral, however,the voltage is 208 volts. This is referred to as the high leg. Thehigh leg can be calculated by multiplying the phase A toneutral voltage times 1.732 (120 x 1.732 = 208). Single-polebreakers should not be connected to the high leg. NEC Article215-8 requires that the high leg bus bar or conductor bepermanently marked with a finish that is orange in color. Thiswill help prevent electricians from connecting 120 volt single-phase loads to the 208 volt high leg. Four-wire, delta-con-nected transformers should always be wired so that the Bphase is the high leg. Not all panelboards are suitable for useon a high leg system. Siemens SE, S4, S5, F1 and F2panelboards are available for use on a high leg system. YourSiemens sales representative should be contacted for furtherinformation.

A - B 240 voltsB - C 240 voltsC - A 240 voltsA - N 120 voltsB - N 208 voltsC - N 120 volts

240 volts

240 volts 120 volts

240 volts

B

A

C

N

208 volts

120 volts

"B" Phase Bus Bar

Three-phase, four-wire,delta-connectedtransformers

38

Service Entrance Panelboards

Sometimes panelboards are used as service entranceequipment for a building. This is the equipment locatednear where the power supply enters the building. Theincoming power supply is connected to this equipmentwhich provides a means to control and cut off thesupply. The National Electrical Code discusses serviceentrance equipment in Article 230. Panelboards usedas service entrance equipment must be approved andlabeled as such. All Siemens Sentron� Seriespanelboards are factory labeled as suitable for serviceentrance equipment when NEC requirements are met.

Service Entrance

Meter

Panelboard

Transformer

39

Service-entrance conductors must have a readily accessiblemeans of being disconnected from the power supply. NECArticle 230-71a specifies that for each set of service entranceconductors no more than six switches or circuit breakersshall be used to disconnect and isolate the service from allother equipment. There are two ways panelboards can beconfigured to meet this requirement. In one example, a mainbreaker panelboard is used. A single main circuit breaker willdisconnect power to all equipment being supplied by theservice. In another example, a main lug only panelboard isequipped with up to six circuit breakers to disconnect powerto all equipment being supplied by the service. In any case,the circuit breaker must be clearly labeled for the load itsupplies.

Main BreakerWith Branch Circuits

Main Lug OnlyWith Six Service Disconnects

Maximum number ofdisconnects for serviceentrance equipment

40

NEC Article 230-71b states that two or three single-poleswitches or circuit breakers, capable of individual operation,shall be permitted on multiwire circuits, one pole for eachungrounded conductor, as one multiple disconnect, providedthey are equipped with �handle ties� or a �master handle� todisconnect all conductors of the service with no more thansix operations of the hand.

It is important to note that the �six disconnect rule� refers tothe number of disconnects and not the number of poles. Forexample, the main lug only panelboard shown below has 18poles but only six circuit breakers. Three poles are mechani-cally linked together to form one disconnect device. In theillustrated configuration the service can be disconnected withno more than six operations of the hand. This arrangementmeets the �six disconnect rule�.

1

2

3

4

5

6

Single-pole units and thesix disconnect rule

41

Panelboard Grounding

Grounding is an important aspect of any electrical equipmentand must be considered carefully. Article 250 of the NECcovers mandatory grounding requirements. The NationalElectrical Code defines ground as a conducting connection,whether intentional or accidental, between an electricalcircuit or equipment and the earth, or to some conductingbody that serves in place of the earth.

The following illustration, for example, shows the neutral (N)conductor of a wye-connected transformer connected toground.

N

Ground

There are two objectives to the intentional grounding ofelectrical equipment:

� Keep potential voltage differentials between differentparts of a system at a minimum which reduces shockhazard.

� Keep impedance of the ground path to a minimum. Thelower the impedance the greater the current is in theevent of a fault. The greater the current the faster anovercurrent device will open.

42

The circuit is grounded only at the service entrance, never atany downstream equipment. In the following illustration theneutral is grounded at the service equipment by connecting agrounding electrode conductor from the neutral (groundedconductor) to a grounding electrode. The neutral and thepanelboard enclosure are bonded together at the serviceequipment so that the enclosure is also connected to groundthrough the grounding electrode connector.

GroundingElectrode Conductor

Grounding Electrode

NeutralBonded To Can

Wall

N

Power Source

Panelboard(Service Entrance)

Neutral Bus

Service entrancegrounding

43

A panelboard may also require an equipment grounding buswhich is non-insulated and mounted inside the panelboarddirectly to the can. All feeder and branch circuit equipmentthat are connected to the equipment grounding bus are at thesame potential as the panelboard can. Siemens panelboardscome with an equipment grounding bus.

EquipmentGrounding Bus

The neutral (grounded conductor) is only connected toground at the service entrance. Beyond the service equip-ment the neutral is always insulated. When a downstreampanel is used the neutral is insulated in that panel. As shownin the following illustration the enclosure of the downstreampanel is connected to ground through a grounding conductorback to the service equipment.

N

Power Source Panelboard(Service Entrance)

Neutral

Equipment Ground

Panelboard(Downstream)

Load #1 Load #2

Insulated NeutralBonded To Can

Equipment GroundBonded To Can

Sub-Feed

MainBranch

Equipment grounding bus

Grounding downstreampanelboards

44

In the following illustration load #2 has become shorted to itsmetal enclosure. Fault current is returned to the sourcethrough the path indicated. With a properly coordinatedsystem the branch circuit breaker in the downstreampanelboard will open removing the load from the powersource. For a discussion of circuit breaker coordination referto the STEP 2000 course, Molded Case Circuit Breakers.

N

Power Source Panelboard(Service Entrance)

Neutral

Equipment Ground

Panelboard(Downstream)

Load #1 Load #2

Insulated NeutralBonded To Can

Equipment GroundBonded To Can

Sub-Feed

MainBranch

Short ToGround

Using the neutral withservice entrance anddownstream panelboards

45

1. If the secondary of a four-wire, wye-connected trans-former is 480 volts phase-to-phase, the phase toneutral voltage is ____________ volts.

2. If the secondary of a four-wire, delta-connectedtransformer is 240 volts phase-to-phase, the phase toneutral voltage is

____________ volts from A-N

____________ volts from B-N

____________ volts from C-N

3. According to NEC Article 230-71a, the maximumnumber of circuit breakers that can be used to dis-connect and isolate the service from all other equip-ment is ____________ .

4. ____________ is the permanent joining of metallicparts to form an electrically conductive path.

5. The ____________ conductor is grounded only at theservice entrance equipment, never at any down-stream equipment.

Review 4

46

Ground Fault Protection

In addition to ensuring equipment is properly grounded,ground fault protection for people and equipment is also aconcern. NEC Article 230-95 states that ground-fault protec-tion of equipment shall be provided for solidly grounded wyeelectrical services of more than 150 volts to ground, but notexceeding 600 volts phase-to-phase for each service discon-necting means rated 1000 amperes or more. Althoughground-fault protectors are not required on service discon-nects that are less than 1000 amperes, depending on theinstallation, they still may be desirable. Ground fault inter-rupters designed to provide life protection must open acircuit at 5 milliamps (± 1 milliamp). Equipment protectionmust open a circuit when ground fault current reaches 30milliamps. Ground fault protection is generally incorporatedinto a special type of circuit breaker.

One way a ground fault protector works is to install a sensoraround the insulated neutral bonding jumper. When an un-balanced current from a line-to-ground fault occurs currentwill flow in the bonding jumper. When the current reachesthe setting of the ground-fault sensor the shunt trip opensthe circuit breaker, removing the load from the line.

480 volts

480 volts

480 volts

A

B

C

N

RelayGround Fault Sensor

Circuit Breaker WithShunt Trip Option

Service Equipment(1000 Amps Or More)

Bonding Jumper

Ground-fault sensor aroundbonding jumper

47

Another way a ground fault protector works is with a sensorinstalled around all the circuit conductors. During normalcurrent flow the sum of all the currents is zero. However, aground fault will cause an unbalance of the currents flowingin the individual conductors around the sensor. When thiscurrent reaches the setting of the ground-fault sensor theshunt trip opens the circuit breaker.

480 volts

480 volts

480 volts

A

B

C

N

Relay

Ground FaultSensor

Circuit Breaker WithShunt Trip Option

Service Equipment(1000 Amps Or More)

Load

Ground-fault sensoraround all circuitconductors

48

Full rating

Panelboard Ratings

When selecting panelboards and overcurrent protectiondevices it is extremely important to know both the maximumcontinuous amperes and available fault current. NEC article110-9 states:

Equipment intended to break current at fault levels shallhave an interrupting rating sufficient for the system voltageand the current which is available at the line terminals of theequipment.

Equipment intended to break current at other than faultlevels shall have an interrupting rating at nominal circuitvoltage sufficient for the current that must be interrupted.

There are two ways to meet this requirement. The full ratingmethod is to select circuit protection devices with individualratings equal to or greater than the available fault current.This means that, in the case of a building with 65,000amperes of fault current available at the service entrance,every circuit protection device must be rated at 65,000amperes interrupting capacity (AIC). In the followingexample, the main circuit breaker and each branch breaker israted for 65,000 AIC.

Main Breaker (65,000 amps)

Branch Breakers (65,000 amps)

49

Series-rated The series-rated concept is that the main upstream circuitprotection device must have an interrupting rating equal to orgreater than the available fault current of the system, butsubsequent downstream circuit protection devices connectedin series can be rated at lower values. For example, a buildingwith 42,000 amperes of available fault current might have thebreaker at the service entrance rated at 42,000 AIC and addi-tional downstream breakers rated at 18,000 AIC.

HED4 Main Breaker (42,000 amps)

ED4 Feeder Breakers (18,000 amps)

Series-rated breaker combinations must be tested in series inorder to be UL listed. Siemens series-rated breakers are listedin the UL �Recognized Components Directory� (yellow books)Volume 1. Selected series-rated breakers are listed in theSpeedfax catalog. Your Siemens sales engineer can providemore information on Siemens series-rated circuit breakers.

There are three rating terms that need to be understoodwhen selecting panelboards and appropriate circuit protec-tion devices.

Withstand Rating Refers to the level of fault current apiece of equipment can withstandwithout sustaining damage. Siemenspanelboards have withstand ratingsup to 200,000 amps.

Interrupting Rating Refers to the current rating a protec-tive device such as a fuse or circuitbreaker can safely interrupt. Siemensmolded case circuit breakers haveinterrupting ratings up to 200,000amps.

Integrated Equipment Refers to the interrupting rating ofthe lowest installed device, unlessthere is a series combination rating,not to exceed the withstand rating ofthe equipment.

Rating terms

50

Integrated equipmentshort circuit rating

The term Integrated Equipment Short Circuit Rating refers tothe application of series circuit breakers in a combination thatallows some breakers to have lower individual ratings thanthe available fault current. This is permitted as long as theseries combinations shown have been tested and certified byUL. The following table from the Speedfax catalog shows S1,S2 and SE assembled panelboards. An SE main breaker (MB)panelboard, for example, can have a main breaker with amaximum continuous ampere rating of 600 amps, branchcircuit breakers with ratings from 15-125 amps, and if usedon 480Y/277V has a short circuit interrupting rating of150,000 amps.

To select appropriate main and branch circuit breakers referto the integrated short circuit ratings tables in the Speedfaxcatalog.

51

1. Ground fault protection is required when service dis-connecting devices are rated at ____________ ormore.

2. The ____________ rating method requires selectingcircuit protection devices with individual ratings equal toor greater than the available fault current.

3. Devices selected for integrated equipment applicationmust be tested and certified by ____________ .

4. ____________ rating refers to the level of fault currenta piece of equipment can withstand without sustainingdamage.

5. ____________ rating refers to the current rating aprotective device such as a fuse or circuit breaker cansafely interrupt.

6. ____________ ____________ refers to the interruptingrating of the lowest installed device, unless there is aseries rating, not to exceed the withstand rating of theequipment.

Review 5

52

S1, S2, And SE Lighting Panelboards

The smallest Sentron� panelboards are the S1, S2, and SEpanelboards. They are available with 18, 30 or 42 circuits.

53

The following chart shows the dimensions of the S1, S2, andSE panelboards. Width and depth varies with the currentrating. Height varies with the number of circuits. The mainbreaker or lug module do not affect panelboard height.

The S1 panelboard is available as a main circuit breaker or amain lug unit. A standard feature of the S1 panelboard is fieldconvertible mains. This means that the panelboard can bechanged from a main circuit breaker to a main lug only in thefield, without increasing box height. Another advantage to theS1 panelboard is the ability to change in the field whether thepanelboard is top or bottom fed. This is accomplished bysimply inverting the panelboard interior or reinstalling themain breaker or lug module on the opposite end of thepanelboard. S1 panelboards also feature concealed fastenersand hinges with a flush door lock.

Dimensions

S1 panelboard

54

The following information gives various S1 rating ranges.Refer to the Speedfax catalog when ordering specificpanelboards. The type of branch, main and subfeed breakersvary with the panelboard and application requirements. Onlyone subfeed breaker is allowed in the S1 panelboard, except400 A and 600 A panelboards can have two QJ subfeedbreakers.

S2 panelboards are similar to S1 panelboards with a fewexceptions. The S2 is designed to operate at voltages of480Y/277 VAC and 600Y/347 VAC. The S2 is suitable for3-phase, 4-wire systems. The S2 panelboard features thesame convertible mains, concealed fasteners, hinges andflush door lock as the S1.

S2 panelboards

55

The following information gives various S2 rating ranges.Refer to Siemens Speedfax when ordering specificpanelboards. The type of branch, main and subfeed breakersvary with the panelboard and application requirements. Onlyone subfeed breaker is allowed in the S2 panelboard, except400 A and 600 A panelboards can have two QJ subfeedbreakers.

SE panelboards are similar to S2 panelboards with a fewexceptions. The SE is designed to operate at a maximumvoltage of 600 VAC/250 VDC. The SE is suitable for1-phase, 3-wire, 3-phase, 3-wire, and 3-phase, 4-wire sys-tems. The SE panelboard features the same convertiblemains, concealed fasteners, hinges and flush door lock as theS1 and S2.

SE panelboards

56

The following information gives various SE rating ranges.Refer to Siemens Speedfax when ordering specificpanelboards. The type of branch, main and subfeed breakersvary with the panelboard and application requirements. Onlyone subfeed breaker is allowed in the SE panelboard, except400 A and 600 A panelboards can have two QJ subfeedbreakers.

57

Transient Protection System (TPS)

Transients voltage spikes appear on an electrical system as aresult of lightning and switching transients. These transientsare capable of destroying sensitive electronic equipment incommercial and industrial applications.

Transient Voltage Spikes

The most damaging voltage spikes are caused by lightingstrikes. Although lightning strikes on high voltage lines aregenerally dissipated by utility transmission and arresters, alighting strike on a power line several miles away still has thepotential to cause extensive electrical damage. Damage toexpensive electrical equipment can be either instantaneous orcumulative.

Need for surge protection

58

Worldwide there are 44,000 thunderstorms each day, 2000thunderstorms at any given time, and 1000 lighting flashesper second. A typical lightning strike consists of 25,000 ampsat 30 million volts. The following map shows the approximatemean annual number of days with thunderstorms in theUnited States.

Computers and other office equipment are susceptible to thehigh energy levels caused by an electrical surge, whether it iscaused by electrical equipment or lightning. Any componentbetween the source of the surge and ground can be dam-aged. Siemens TPS transient protection system clamps thesedamaging voltage spikes before they damage expensive andsensitive equipment.

TPS

Number of thunderstorms

TPS

59

The TPS is bolted directly to the bus bars within the S1, S2,and SE panelboards. Purchased �over the counter� and utiliz-ing a field installation kit, the TPS transient voltage protectionsystem can easily be mounted in existing S1, S2, and SElighting panelboards. LEDs indicate that the device is workingand provide voltage and diagnostic monitoring. There is anaudible alarm and test button. Options include a surgecounter and a remote monitoring device.

TPS with LED indicators,audible alarm with silence

switch, and test button.

Clamping voltage is the amount of voltage allowed across asurge suppression device when it is conducting a specificcurrent created by a surge. The following chart indicatesclamping voltage for the Siemens TPS.

System Voltage Line-to-Neutral Neutral-to-Ground Line-to-Ground

120/240 1Ø3W

208Y/120V 3Ø4W

480Y/277V 3Ø4W

500 V

500 V

1000 V

500 V

500 V

1000 V

500 V

500 V

1000 V

Peak current rating specifies the maximum current that aprotective device can withstand from a single surge. TheSiemens TPS can withstand impulse currents as high as80,000 amps or 160,000 amps, depending on the model.

Installation

Clamping voltage

Peak current rating

60

1. The maximum number of circuits available on theS1, S2, and SE lighting panelboards is ____________ .

2. One way to convert an S1, S2, or SE from top tobottom feed is to relocate the main breaker or lugmodule. Another way is to ____________ the interior.

3. The maximum voltage of an S1 panelboard is____________ volts.

4. The maximum integrated equipment short circuitrating of an S2 panelboard is ____________ AIR.

5. The maximum voltage rating for an SE panelboard is____________ VAC.

6. The ____________ ____________ ____________ isused to protect sensitive electrical equipment fromdamaging voltage spikes.

Review 6

61

S4 And S5 Power Panelboards

S4 and S5 power panelboards are similar in design andfeatures, but vary in the ratings available. S4 and S5panelboards will accept various circuit breakers and fusibleswitches. The S4 will accept branch circuit breakers up to 600amps. The S5 will accept branch circuit breakers up to 1200amps.

62

The following information gives various S4 rating ranges.Refer to Siemens Speedfax when ordering specificpanelboards. Branch circuit breakers vary depending on thepanelboard rating.

The following information gives various S5 rating ranges.Refer to Siemens Speedfax when ordering specificpanelboards. Branch circuit breakers vary depending on thepanelboard rating.

The S4 is only 32� wide by 10� deep. This simplifies handlingand installation. The enclosure height varies with the typeand number of circuits required. The enclosure heights are60�, 75� and 90�. A one piece door is available which allowsfor locking and flush mounting.

The S5 is 38� wide by 12.75� deep in a NEMA Type 1 enclo-sure. The S5 is 38� wide by 14.25� deep in a NEMA Type 3Ror 12 enclosure. The enclosure height varies with the typeand number of circuits required. The enclosure heights are60�, 75� and 90�.

S4 panelboard ratings

S5 panelboard ratings

Dimensions

63

F1 And F2 Fusible Panelboards

F1 and F2 power panelboards normally use fusible switchesfor overcurrent protection instead of circuit breakers. F1 andF2 have main lug ratings up to 1200 A. When main protectionis required, a fusible switch with ratings of 100 and 200 ampsshould be used for F1 panelboards or 400 to 1200 amps forF2 panelboards.

64

Siemens branch fusible switches are available with ampereratings from 30 to 1200 amps.

Siemens fusible switches can be fitted with Class J, L, RK1,RK5 or T fuses. The following illustration shows a Class Rfuse holder.

Fusible switch

65

Siemens Vacu-Break® fusible switches, through 600 A,feature a Clampmatic® action. This action holds the currentcarrying contact surfaces in a vise-like grip. Heat build-up dueto current is minimized. When the switch is moved to the�OFF� position the movable contact snaps from between thejaws providing a quick, clean break. Twin arcs are producedwhich are smaller and extinguish quicker than a single arcproduced by other designs.

The contacts are surrounded by an enclosed arc chamberwhich absorbs much of the heat from the arching. The en-closed chamber helps limit oxygen which aids the coolingand rapid extinguishing of the arcs.

Clampmatic action

Enclosed arc chamber

66

A high contact pressure (HCP) switch is used on switchesrated for 800 A and 1200 A. The HCP switch does not use theVacu-Break® design.

The following information gives various F1 rating ranges.Panelboards are still referred to as main breaker or main lugonly even though fusible disconnects are used. Refer toSiemens Speedfax when ordering specific panelboards.

High contactpressure switch

F1 panelboard ratings

67

The following information gives various F2 rating ranges.Refer to Siemens Speedfax when ordering specificpanelboards.

The F1 is only 32� wide by 10� deep. The enclosure heightvaries with the type and number of circuits required. Theenclosure heights are 60�, 75� and 90�.

The F2 is 38� wide by 12.75� deep in a NEMA Type 1 enclo-sure. The F2 is 38� wide by 14.25� deep in a NEMA Type 3R or12 enclosure. The enclosure height varies with the type andnumber of circuits required. The enclosure heights are 60�,75� and 90�.

F2 panelboard ratings

Dimensions

68

Telephone And Equipment Panelboards

Siemens also manufactures telephone and equipment cabi-nets which conform to requirements of Underwriters Labora-tories, Inc. Cabinets are 5.75� deep, 20 or 24� wide and varyin height from 23 to 65�. All telephone and equipment cabi-nets are preceeded by the letters �TC� in the catalog number.The catalog number also reflects the cabinet height. Forexample, �TCS23B� is a telephone and equipment cabinetthat is 23� in height.

69

Seismic Rated Panelboards

Seismic activity occurs throughout the United States and theworld. The Uniform Building Code (UBC) specifies ratings forthe United States. The following seismic zone map roughlyidentifies seismic activity areas in the United States. Areas inzones with higher numbers experience greater seismic activ-ity than areas in zones with lower numbers.

Siemens panelboards have undergone extensive seismictesting in order to obtain third party certification. Siemenspanelboards will operate in zones 0, 1, 2A, and 2B with nomodification. Panelboards that require zone 3 and 4 ratingsare available with standard lead times.

70

Shunt trip

Accessories

Accessories add to the performance of a panelboard oradapts the panelboard for specific application requirements.Various accessories are available for Siemens panelboards.

Some accessories modify the circuit breaker. For example, itis sometimes necessary to trip a breaker from a remote loca-tion. If someone were to get caught in a piece of machinery,anyone else can push a �panic button� tripping the breaker.One or all critical circuit breakers may be tripped at the pushof a button from a distant control point by use of a shunt tripdevice. The shunt trip may be part of the main breaker whichwill shut off the entire panelboard, or part of a branch breaker.The shunt trip device consists of a coil in series with a limitswitch. When the circuit breaker contacts are closed, the limitswitch is closed. Depressing a customer-suppliedpushbutton energizes the shunt trip coil, causing thebreaker�s mechanical latch to disengage the trip mechanismand opening the circuit breaker�s contacts. When the circuitbreaker�s contacts open, the limit switch also opens, remov-ing power from the shunt trip coil. As with any trip, thebreaker must be reset manually.

Limit Switch

Pushbutton

Coil

Customer Supply

71

The following illustration shows the shunt trip beingmounted on its associated breakers.

Shunt Trip Accessory

Shunt Trip Accessory

Other Sentron SeriesED Frame

Tork, Sangamo or Paragon time clocks are available as anaccessory. Time clocks are available in 1 or 2-pole, single ordouble throw devices, or 3-pole, single throw. They are ratedfor a maximum of 277 volts.

Tork Time Clock

Time clocks

72

A time clock can be used to turn a branch circuit or an entirepanelboard on and off at predetermined times. In the follow-ing illustration, for example, a time clock connected to apanelboard is used to turn outside lights on and off on a smallcommercial building.

Storage Retail

Parking

Lighting

Panelboard

Time Clock

Meter

ASCO 920 switches are mechanically held, two- or three-poleremote control switches may be used as a main circuit dis-connect device when an application calls for a switch to dailyturn blocks of lighting on and off. ASCO 920 switches areavailable in 30, 60, 75, 100, 150, 200 and 225 amperes.Siemens also has a type CLM switch (not shown) which is amechanically held, 20 amp, remote control unit, suitable forall types of lighting loads. It is available in 2, 3, 4, 6, 8, 10 and12 poles.

Remote Control Switch

Remote control switches

73

Catalog Numbers

To help identify each type of panelboard a catalog number isassigned. The catalog number provides a description of thepanelboard. There are eight parts to the standard Sentron�Series panelboard catalog number. The following figure illus-trates a typical catalog number.

S 1 C 4 2 F X 2 5 0 A T S

1 2 3 4 5 6 7 8

Part 1 identifies the type of panel. Panelboard are available inS1, S2, SE, S4, S5, F1and F2 types. The sample panelboardcatalog number shown is an S1 panelboard.

Part 2 identifies the voltage and system. The following tableshows voltage and system configurations available. The lastcolumn identifies the system. 1Ø3W, for example, is a single-phase, three-wire.

A = 120/240V 1Ø3W (S1, SE, S4, S5, F1, F2)B = 240/120V 3Ø4W (SE, S4, S5, F1, F2)C = 208Y/120V 3Ø4W (S1, SE, S4, S5, F1, F2)D = 240V 3Ø3W (SE, S4, S5, F1, F2)E = 480Y/277V 3Ø4W (S2, SE, S4, S5, F1, F2)F = 480V 3Ø3W (SE, S4, S5, F1, F2)G = 600V 3Ø3W (SE, S4, S5, F1, F2)L = 600Y/347V 3Ø4W (S2, SE, S4, S5, F1, F2)N = 120 VDC 2W (SE, S4, S5, F1, F2)O = 250 VDC 2W (SE, S4, S5, F1, F2)

Part 1

Part 2

74

The panelboard identified in the panelboard example is a208Y/120V, 3Ø4W. This indicates it is rated for a 208 volt wye-connected secondary. There are 208 volts phase-to-phaseand 120 volts phase-to-neutral. It is a 3-phase (3Ø) 4-wire(4W) system.

208 volts

A

B

N

C

208 volts

208 volts

120 volts

120 volts

120 volts

Part 3 indicates the number of circuits in an S1, S2 or SE typepanelboard. If the panelboard is an S4, S5, F1 or F2 type thisnumber represents the enclosures height in inches. In thisexample the panelboard is an S1. There are 42 circuits.

Part 4 indicates whether the panelboard is a main breaker(2-digit code varies for each different circuit breaker), mainlug (ML) or main switch (MS). In this example the panelboardis an FXD6 main breaker (FX).

Part 5 indicates the panelboard current rating. The examplepanelboard is rated for 250 amps.

Part 6 indicates the bus material. The following table showsbus materials available. In this example the panelboard hasstandard aluminum bus bars.

A = Tin Plated Aluminum Temp Rated (standard)B = 750A/in2 Aluminum (optional)C = Copper Temp Rated (optional)D = 1000A/in2 Copper (optional)E = Silver Plated Copper (optional)

Part 3

Part 4

Part 5

Part 6

75

Part 7 indicates whether feed location is from the top (T) orbottom (B). In this example the panelboard is top fed.

Part 8 indicates whether the panelboard is surface mounted(S) or flush mounted (F). In this example the panelboard issurface mounted.

Part 7

Part 8

76

Information Needed To Order Panelboards

When ordering a panelboard several questions need to beanswered.

1. What is the system (voltage, phases, number of wires)?

2. What is the AIC rating (ampere interrupting capacity)?

3. What is the NEMA Type enclosure desired?

4. How many circuits are required?

5. Does the panelboard need to be suitable for serviceentrance?

Suitable for use on service entrance Labels (SUSE) areavailable provided NEC requirements are met. A mainlug only panelboard, for example, can only have a maxi-mum of 6 breakers or it violates the 6 disconnect rule.

6. What amperage is the panelboard rated at?

7. Will the panelboard be main breaker or main lug only?

8. What special modifications are needed?

9. What is the shipping time frame?

10. Is the panelboard to be top or bottom fed?

11. Is the panelboard to be surface or flush mount?

12. Is the panelboard assembled or unassembled?

77

1. The S4 panelboard will accept branch circuit break-ers up to ____________ amps.

2. The maximum main circuit breaker available for theS5 panelboard is ____________ amps.

3. F1 and F2 panelboards use ____________ switchesfor branch circuit protection.

4. The enclosed arc chamber limits ____________which aids in the cooling and rapid extinguishing ofthe arcs.

5. The maximum main circuit breaker available for F1panelboards is rated for ____________ amps.

6. A ____________ ____________ accessory mounts tothe circuit breaker and is used to trip a breaker froma remote location.

7. A letter ___________ in part 2 of a catalog numberwould indicate a 120/240 volt, 1-phase, 3-wire sys-tem.

8. The number 42 in part 3 of a catalog number for anS1 panelboard indicates the panelboard

a. contains 42 circuitsb. is 42 inches tallc. is 42 inches wide

Review 7

78

Review 1

Review Answers

1) distribution system; 2) b; 3) 384; 4) lighting and appliancebecause there are less than 42 poles and more than 10% arerated 30 amps or less.

1) bus; 2) current; 3) overload, short circuit, ground;4) 50,000 amps; 5) R; 6) amps, voltage;7) deadfront and trim; 8) 1.

1) breaker, lug; 2) horizontally or vertically; 3) lug only;4) feed-through; 5) 384-16; 6) two.

1) 277; 2) 120 A-N, 208 B-N, 120 C-N; 3) 6; 4) Bonding;5) neutral.

1) 1000 A; 2) full; 3) UL; 4) Withstand; 5) Interrupting;6) Integrated Equipment.

1) 42; 2) invert; 3) 240; 4) 200,000; 5) 600; 6) TransientProtection System

1) 600; 2) 1200; 3) fusible; 4) oxygen; 5) 600; 6) shunt trip;7) a; 8) a.

Review 2

Review 3

Review 4

Review 5

Review 6

Review 7

79

Questions

Final Exam

The final exam is intended to be a learning tool. The bookmay be used during the exam. A tear-out answer sheet isprovided. After grading the test, mail the answer sheet in forgrading. A grade of 70% or better is passing. Upon successfulcompletion of the test a certificate will be issued. Thosereceiving a score of less than 70% will be provided a secondtest.

1. Which of the following is not a requirement for a lightingand appliance panelboard?

a. A neutral connection must be provided.b. A maximum of 42 overcurrent devices are

allowed.c. More than 10% of the overcurrent devices must

be rated 30 amps or less.d. Must be connected to the secondary of a 4-wire,

3-phase, wye-connected transformer.

2. Panelboards are covered by NEC article ____________ .

a. 110 b. 240c. 384 d. 430

3. The AIC rating of a Class R fuse is ____________ amps.

a. 10,000 b. 50,000c. 100,000 d. 200,000

4. The item used to cover any unused pole spaces notfilled by a circuit breaker is a ____________ .

a. deadfront b. QF3 filler platec. trim d. label

5. The type of enclosure intended for outdoor use

80

primarily to provide a degree of protection against rain,sleet and damage from external ice formation is___________ .

a. Type 1 b. Type 3Rc. Type 4X d. Type 3R/12

6. The required distance in front of a panelboard door andsufficient to allow the hinged door to open 90° is____________ .

a. 30 inches b. 4 feetc. 3 feet d. 6 1/2 feet

7. Two types of panelboards are ____________ .

a. main breaker and sub-feedb. main lug only and sub-feedc. main breaker and main lug onlyd. sub-feed and feed-through

8. On a three-phase, four-wire, wye-connected transformerwith a secondary voltage of 480 volts phase-to-phase,the phase-to-neutral voltage is _________ volts.

a. 277 b. 240c. 138 d. 480

9. On a three-phase, four-wire, delta-connected transformerthe high leg is ____________ .

a. A - N b. B - Nc. C - N d. A - B

10. The maximum number of switches or circuit breakersused to disconnect and isolate the service from all otherequipment on service-entrance equipment is ________ .

a. 1 b. 2c. 4 d. 6

11. The neutral conductor is ____________ grounded at theservice-entrance panelboard.

a. always b. neverc. rarely d. often

12. The neutral conductor is ____________ grounded atpanelboards downstream from the service-entrancepanelboard.

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a. always b. neverc. rarely d. often

13. Article 230-95 of the NEC states that ground-fault protec-tion of equipment shall be provided for solidly groundedwye electrical services of more than 150 volts to ground,but not exceeding 600 volts phase-to-phase for eachservice disconnecting means rated ____________ am-peres or more.

a. 5 milliamps b. 10 ampsc. 1000 amps d. 200,000 amps

14. The rating which refers to the interrupting rating of thelowest installed device, unless there is a series combina-tion rating, not to exceed the withstand rating of theequipment is the ____________ rating.

a. full b. withstandc. interrupting d. integrated equipment

15. The number �60� in part 3 of the catalog number of an F1panelboard indicates the panelboard ____________ .

a. is 60�� wide b. has 60 circuitsc. is 60� high d. is rated for 60 amps

16. The height of an S1 panelboard with 42 circuits is____________ inches.

a. 32 b. 38c. 42 d. 44

17. Which of the following branch breakers can be used onan S2 panelboard?

a. BQD b. BLc. BLH d. HBL

18. The maximum current rating of an S5 panelboard is____________ amps.

a. 1200 b. 600c. 100,000 d. 200,000

19. The F1 panelboard is ____________ inches wide.

a. 10 b. 32

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c. 38 d. 60

20. The line-to-neutral clamping voltage of the Siemens TPSis ____________ volts on a 120/240 1Ø3W system.

a. 225 b. 1000c. 500 d. 80,000

83

Notes

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Notes