meeting nec for selective coordination

Meeting the NEC Meeting the NEC Selective Selective

CoordinationCoordinationRequirementsRequirements

Robert E. Fuhr, P.E.Robert E. Fuhr, P.E.

Power Systems EngineeringCovington, WA

AgendaAgenda

NEC Code RequirementsNEC Code RequirementsDefinitionsDefinitionsFuse Selective CoordinationFuse Selective CoordinationBreaker Trip Unit TypesBreaker Trip Unit TypesBreaker Selective CoordinationBreaker Selective CoordinationProcedure to Achieve Selective CoordinationProcedure to Achieve Selective Coordination–– FusesFuses–– BreakersBreakers

ExamplesExamples

Fuses vs. Fuses vs. Circuit Circuit

BreakersBreakers

Special ThanksSpecial Thanks

Square D CompanySquare D CompanyData BulletinData Bulletin““Enhancing Short Circuit Selective Enhancing Short Circuit Selective Coordination with Low Voltage BreakersCoordination with Low Voltage Breakers””http://ecatalog.squared.com/pubs/Circuithttp://ecatalog.squared.com/pubs/Circuit%20Protection/0100DB0403.pdf%20Protection/0100DB0403.pdf

Emergency SystemsEmergency Systems

700.27 Coordination.700.27 Coordination.–– Emergency system(s) overcurrent devices Emergency system(s) overcurrent devices

shall be shall be selectively coordinatedselectively coordinated with with allall supply supply side overcurrent protective devices.side overcurrent protective devices.

ARTICLE 701 Legally Required ARTICLE 701 Legally Required Standby SystemsStandby Systems

701.18 Coordination.701.18 Coordination.–– Legally required standby system(s) Legally required standby system(s)

overcurrent devices shall be overcurrent devices shall be selectively selectively coordinatedcoordinated with with allall supply side overcurrent supply side overcurrent protective devices.protective devices.

ARTICLE 620 Elevators, ARTICLE 620 Elevators, Dumbwaiters, Escalators, Moving Dumbwaiters, Escalators, Moving

Walks, Wheelchair Lifts, and Walks, Wheelchair Lifts, and Stairway Chair LiftsStairway Chair Lifts

620.62 Selective Coordination.620.62 Selective Coordination.–– Where more than one driving machine Where more than one driving machine

disconnecting means is supplied by a single disconnecting means is supplied by a single feeder, the overcurrent protective devices in feeder, the overcurrent protective devices in each disconnecting means shall be each disconnecting means shall be selectively selectively coordinatedcoordinated with any other supply side with any other supply side overcurrent protective devices.overcurrent protective devices.

ARTICLE 517 Health Care FacilitiesARTICLE 517 Health Care Facilities

Essential Electrical Systems must meet Essential Electrical Systems must meet Section 700 (except as amended by 517)Section 700 (except as amended by 517)ImpliesImplies that Essential Electrical Systems that Essential Electrical Systems must be must be selectively coordinatedselectively coordinated. (700.27 & . (700.27 & 701.18)701.18)

ARTICLE 100 DefinitionsARTICLE 100 Definitions

Coordination (Selective). Coordination (Selective). –– Localization of an overcurrent condition to Localization of an overcurrent condition to

restrict outagesrestrict outages to the to the circuitcircuit or or equipment equipment affectedaffected, accomplished by the choice of , accomplished by the choice of overcurrent protective devices and their overcurrent protective devices and their ratings or settings.ratings or settings.

517.2 Definitions517.2 Definitions

Emergency System. Emergency System. –– A A systemsystem of circuits and equipment intended of circuits and equipment intended

to to supply alternate powersupply alternate power to a limited number to a limited number of prescribed functions vital to the protection of prescribed functions vital to the protection of life and safety.of life and safety.


Legally Required Standby Systems. Legally Required Standby Systems. –– Those systems required and so classed as Those systems required and so classed as

legally required standby by municipal, state, legally required standby by municipal, state, federal, or other codes or by any federal, or other codes or by any governmental agency having jurisdiction. governmental agency having jurisdiction. These These systemssystems are intended to are intended to automatically automatically supply power to selected loadssupply power to selected loads (other than (other than those classed as emergency systems) in the those classed as emergency systems) in the event of failure of the normal source.event of failure of the normal source.


FPN:FPN:–– Legally required standby systems are Legally required standby systems are

typically installed to serve loads, such as typically installed to serve loads, such as heating and refrigeration systems, heating and refrigeration systems, communications systems, ventilation and communications systems, ventilation and smoke removal systems, sewage disposal, smoke removal systems, sewage disposal, lighting systems, and industrial processes, lighting systems, and industrial processes, that, that, when stoppedwhen stopped during any interruption of during any interruption of the normal electrical supply, the normal electrical supply, could create could create hazards or hamper rescue or firehazards or hamper rescue or fire--fighting fighting operations.operations.


Essential Electrical System. Essential Electrical System. –– A A systemsystem comprised of alternate sources of comprised of alternate sources of

power and all connected distribution systems power and all connected distribution systems and ancillary equipment, and ancillary equipment, designed to ensure designed to ensure continuity of electrical powercontinuity of electrical power to designated to designated areas and functions of a health care facility areas and functions of a health care facility during disruption of normal power sources, during disruption of normal power sources, and also and also designed to minimize disruption designed to minimize disruption within the internal wiring systemwithin the internal wiring system..

DefinitionsDefinitions

MCCB MCCB –– Molded Case Molded Case Circuit BreakerCircuit Breaker


ICCB ICCB –– Insulated Case Circuit BreakerInsulated Case Circuit Breaker


LVPCB LVPCB ––Low Low Voltage Voltage Power Power Circuit Circuit BreakerBreaker

Time Current CurvesTime Current Curves

Time Current Curve (TCC)Time Current Curve (TCC)The logThe log--log graph of time versus current.log graph of time versus current.Each breaker, fuse, and relay has a time Each breaker, fuse, and relay has a time current characteristic curve current characteristic curve

Fuse Fuse TCCTCC

3-6 Sec

5 kA

@15 kA

This Fuse is Current Limiting –Clearing time is 0.004 seconds

Thermal Thermal Magnetic Magnetic BreakerBreaker

20 kA0.01-0.025 Sec

4 kA

20-50 Sec

Solid Solid State TripState Trip

SQ D NW SQ D NW 40H40H4000 Amp4000 AmpMicrologicMicrologic

100 kA

0.01-0.06 Sec

6 kA

0.08-0.12 Sec 30 kA

170-210 Sec

Manufacture Manufacture TCCTCC


ManufactManufacture TCCure TCC


What is Selective Device What is Selective Device Coordination Coordination

Devices closest to the fault must operate Devices closest to the fault must operate first.first.Upstream devices trip in sequenceUpstream devices trip in sequenceNo overlap on TCCsNo overlap on TCCs

Sample Sample One LineOne Line 3-MSWBD MAIN

SWBD

XFMR-UTILSS

P 2- XFMR-UTILS

5-Fdr to ATS-E

6-PNL-A MAIN

PNL-A - 250 A

E N

ATS 260 Amp

11

22

33

Selective Selective CoordinaCoordina--

tiontionThree Three Breakers in Breakers in SeriesSeriesNo OverlapNo OverlapEasy Right?Easy Right?

Problems with this Code Problems with this Code Requirement Requirement -- FusesFuses

Requires larger equipment than using T/M Requires larger equipment than using T/M CBsCBsLarger Electrical Room Larger Electrical Room –– Less rental or Less rental or usable building spaceusable building spaceReduces Levels of downstream equipmentReduces Levels of downstream equipmentFusible Panelboards and Elevator Modules Fusible Panelboards and Elevator Modules are more expensive than T/M circuit are more expensive than T/M circuit breakersbreakers

Problems with this Code Requirement Problems with this Code Requirement ––Circuit BreakersCircuit Breakers

Most breakers have an instantaneous trip Most breakers have an instantaneous trip function.function.–– Breaker trips instantaneously (no time delay)Breaker trips instantaneously (no time delay)

No Selective Coordination Testing for No Selective Coordination Testing for Thermal/Magnetic BreakersThermal/Magnetic BreakersLimited equipment w/o InstantaneousLimited equipment w/o InstantaneousHigher fault current = Increases Higher fault current = Increases complexity to selectively coordinatecomplexity to selectively coordinate

Problems with this Code Requirement Problems with this Code Requirement ––Circuit BreakersCircuit Breakers

Requires larger frame breakers with Solid Requires larger frame breakers with Solid State Trip unitsState Trip unitsLarger Framed Breakers Means Larger Larger Framed Breakers Means Larger Electrical Room Electrical Room -- Less rental or usable Less rental or usable building spacebuilding spaceNot all trip units function the same way Not all trip units function the same way Difficult to obtain competitive bidsDifficult to obtain competitive bids

RealityReality

Very Expensive to Design and Very Expensive to Design and ComplyComply

This new Section of the code will This new Section of the code will radically change the way we all radically change the way we all design emergency and standby design emergency and standby

power systems.power systems.

Real Problem or a Perceived Real Problem or a Perceived (Paper) Problem?(Paper) Problem?

On paper, breakers with instantaneous trip On paper, breakers with instantaneous trip units will not coordinate.units will not coordinate.In the real world…is this a problem?In the real world…is this a problem?How many times has this happened to How many times has this happened to you?you?–– Incorrect trip unit settings do not countIncorrect trip unit settings do not count–– Poor maintenance or defective trip units do Poor maintenance or defective trip units do

not countnot count

Selective Coordination Selective Coordination -- FusesFuses

FusesFuses have been have been testedtested for for coordinationcoordination..Relatively Relatively easyeasy toto select equipment to select equipment to coordinatecoordinate..Pick FusesPick Fuses from Manufacturer’s Fuse from Manufacturer’s Fuse Selective Coordination ChartsSelective Coordination Charts

FerrazFerraz--ShawmutShawmut1600 Ampere Main1600 Ampere Main

600 Ampere Branch600 Ampere Branch

BussmannBussmann

Fuse not in ChartFuse not in Chart

Fuse Fuse II22tt is the is the best toolbest tool for assuring for assuring coordinationcoordinationTotal clearing ITotal clearing I22tt of the of the downstreamdownstream fuse fuse << melting Imelting I22tt of the main of the main upstreamupstream fusefuse

Selective Coordination Selective Coordination –– FusesFuses

Most ratios are 2:1 or higherMost ratios are 2:1 or higherReduces # of Levels of CoordinationReduces # of Levels of CoordinationExample Example –– 1600 Ampere Main (6 Levels)1600 Ampere Main (6 Levels)–– Feeder 1 Feeder 1 –– 800 Ampere800 Ampere–– Feeder 2 Feeder 2 –– 400 Ampere400 Ampere–– Feeder 3 Feeder 3 –– 200 Ampere200 Ampere–– Feeder 4 Feeder 4 –– 100 Ampere100 Ampere–– Feeder 5 Feeder 5 –– 50 Ampere50 Ampere–– Feeder 6 Feeder 6 –– 25 Ampere25 Ampere

Fused PanelboardsFused Panelboards

BussmannBussmann Coordination Module™Coordination Module™

208/120 & 277/480 V208/120 & 277/480 V200 Ampere Maximum200 Ampere MaximumMain Lug Only (MLO)Main Lug Only (MLO)12, 24, 36, & 42 Circuits12, 24, 36, & 42 CircuitsBranch Circuit 0Branch Circuit 0--30 Amperes30 AmperesShort Circuit Rating Short Circuit Rating –– 100 kA100 kA

Issues with FusesIssues with Fuses

Upstream FusesUpstream Fuses with with Downstream Circuit Downstream Circuit BreakersBreakers–– They have not been tested for Selective They have not been tested for Selective

CoordinationCoordinationMust use all fusesMust use all fusesRare Exception Rare Exception –– Fault current is less than Fault current is less than the current limiting operation of the fuse. the current limiting operation of the fuse. Tip#1 Tip#1 –– Avoid intermixing fuses and Avoid intermixing fuses and circuit breakers.circuit breakers.

Circuit Breaker Trip UnitsCircuit Breaker Trip Units

Thermal MagneticSolid State– LI (Long Time & Instantaneous)– LSI (Long, Short Times & Instantaneous) – LS (Long Time and Short Time)– G (Ground Fault)

Not all Solid State Trip Units are alike!!!

Thermal Magnetic Thermal Magnetic Trip UnitTrip Unit

Thermal Thermal Magnetic Magnetic Trip UnitTrip UnitThermal Thermal Unit is Unit is FixedFixedInstantInstant--aneousaneous–– FixedFixed–– AdjustableAdjustable

Solid Solid State Trip State Trip

UnitUnitVaries for Varies for each Trip each Trip Unit!Unit!Some Some Functions Functions are Not are Not Adjustable!Adjustable!

Long Time Pickup (LTPU)

Long Time Delay (LTD)

Short Time Pickup (STPU)

Short Time Delay (STD)

Instantaneous (I)

Short Time Delay I2T-IN

(I2T)

Solid Solid State Trip State Trip

UnitUnitSQ D NW SQ D NW 40H40H4000 Amp4000 AmpMicrologicMicrologic

Current SensorsRating Plugs

Current Setting

Solid State Trip UnitSolid State Trip Unit

Why is Why is this this

Difficult?Difficult?Three Three Breakers in Breakers in SeriesSeriesNo OverlapNo OverlapEasy Right?Easy Right?


Difficult?Difficult?SWBD MainSWBD Main–– SS w/ LISS w/ LI

FeederFeeder–– SS w/ LSISS w/ LSI

Panel MainPanel Main–– T/MT/M

Panel BranchPanel Branch–– T/MT/M

3-MSWBD MAINSQUARE D NW40H Sensor/Trip 4000 A

SWBD480 V

XFMR-UTILS480 V

S

P 2- XFMR-UTILS

5-Fdr to ATS-ESQUARE D LE Sensor/Trip 250 APlug 250 A

6-PNL-A MAINSQUARE D LA Sensor/Trip 250 A

PNL-A - 250 A480 V

E N

ATS 260 Amp

12-Lrgst FdrSQUARE D FH Sensor/Trip 100 A


Difficult?Difficult?Instantaneous Instantaneous FunctionFunctionPer UL & Per UL & NEMA NEMA ––Required on Required on MCCBs & MCCBs & ICCBsICCBsLVPCBs LVPCBs –– Not Not RequiredRequired

SolutionSolution

EliminateEliminate the Instantaneous Function by:the Instantaneous Function by:–– Reducing the fault currentReducing the fault current–– Setting Instantaneous above fault current.Setting Instantaneous above fault current.

Instantaneous Instantaneous Function Function ––T/M TripT/M Trip

Selectively Selectively coordinates coordinates only if only if difference difference in fault in fault currentcurrent

InstantaneousInstantaneousFunction Function ––

SS TripSS Trip

Instantaneous Instantaneous curve ends at curve ends at available fault available fault currentcurrent100,000 Amps100,000 Amps


SS TripSS Trip



SS TripSS Trip

Adjust Adjust Instantaneous Instantaneous curve above curve above the available the available fault currentfault current3X3X


SS TripSS Trip


Problem Problem –– Large EquipmentLarge Equipment

Switchboard Feeder and Panelboard Mains Switchboard Feeder and Panelboard Mains many times are ICCBmany times are ICCBTip #2 Tip #2 –– Eliminate Main Breakers in Eliminate Main Breakers in Panelboards.Panelboards.

Switchgear & Switchboard

Switchgear and switchboard, Panelboard structures are built and tested to different standards:

SwitchgearSwitchgear

ANSI standard C37.20.1UL standard 1558NEMA standard SG-5Switchgear uses power circuit breakers (PCB) – ANSI C37.13– NEMA SG-3 – UL-1066

Unfused switchgear short circuit tested 30 cycles

SwitchgearSwitchgear

Instantaneous trip function not required for LVPCBs.

SwitchboardsSwitchboards

Group MountedSwitchboards Standards – NEMA PB-2– UL-891.

Switchboards may use a combination of protective devices

Switchboards Switchboards –– Devices to UseDevices to Use

Insulated case (ICCB)Molded-case circuit breakers (MCCB)Fusible switchesPower circuit breakers

GroupGroup--mounted Switchboards,mounted Switchboards, ––Short Circuit TestingShort Circuit Testing

Short Circuit tested for only 3 cyclesProtective devices must have instantaneous for UL 891 labelThis Instantaneous trip function reducesselectivity between the main and feedercircuits breakers.

Compartmented Switchboards

Short Circuit tested for 30 cycles.UL 891 Listed

SWBDSWBD& SWGR & SWGR TestingTesting

ANSI, NEMA, & ANSI, NEMA, & ManufacturersManufacturers….. We need ….. We need an I2T an I2T Withstand Withstand Curve!!!!Curve!!!! SWBD W/S Tested for SWBD W/S Tested for

3 Cycles (0.05 Seconds)3 Cycles (0.05 Seconds)

SWGR W/S 65 KA SWGR W/S 65 KA

@ 30 Cycles (0. 5 Seconds)@ 30 Cycles (0. 5 Seconds)

SWBD W/S 65 KA SWBD W/S 65 KA

More TipsMore Tips

Tip #3Tip #3–– T/M breakers must have a 3:1 ratio to T/M breakers must have a 3:1 ratio to

selectively coordinate.selectively coordinate.

Tip #4Tip #4–– Impedance aids in selective coordinationImpedance aids in selective coordination–– Long feeder lengthsLong feeder lengths–– Air core reactorsAir core reactors–– TransformersTransformers

Tip #5 Tip #5 –– Feeders to Feeders to Downstream MainsDownstream Mains

Feeders to Equipment Main Feeders to Equipment Main Devices, do not need to Devices, do not need to coordinate.coordinate.They feed the same load!They feed the same load!Impossible to do with SS Trip Impossible to do with SS Trip Breakers. (LTPU Region)Breakers. (LTPU Region)Impossible to do with fuses.Impossible to do with fuses.

3-MSWBD MAINSQUARE D NW40H Sensor/Trip 4000 A

SWBD480 V

XFMR-UTILS480 V

S

P 2- XFMR-UTILS

5-Fdr to ATS-ESQUARE D LE Sensor/Trip 250 APlug 250 A

6-PNL-A MAINSQUARE D LA Sensor/Trip 250 A

PNL-A - 250 A480 V

E N

ATS 260 Amp

12-Lrgst FdrSQUARE D FH Sensor/Trip 100 A

11

22

22

33

Panelboard Panelboard Mains Mains -- MCSMCS

Use Caution when Use Caution when using Molded Case using Molded Case Switches (MCS)Switches (MCS)May have very low May have very low self self --protecting protecting instantaneous instantaneous functionfunction

Transformer ProtectionTransformer Protection

NEC Table 450.3(B) Maximum Rating or NEC Table 450.3(B) Maximum Rating or Setting of Overcurrent Protection for Setting of Overcurrent Protection for TransformersTransformersDeltaDelta--Wye LV Transformers requireWye LV Transformers require–– Primary Protection @ Primary Protection @ << 250% 250% ratingrating–– Secondary Protection @ Secondary Protection @ << 125%* 125%* ratingrating–– *Use next highest standard rating allowed *Use next highest standard rating allowed

(see Table 240.6)(see Table 240.6)Tip #6 Tip #6 –– Keep Table 240.6 within reachKeep Table 240.6 within reach

S

P T-3

T-3 PRIM

T-3 SEC

12-Lrgst Brnch

PNL-A - 250 A

13-Pnl C MAIN

PNL-C

Tip #7 Tip #7 –– Primary & Primary & Secondary ProtectionSecondary Protection

Primary & Secondary Devices, Primary & Secondary Devices, do not need to coordinate.do not need to coordinate.They feed the same load!They feed the same load!Difficult to do with fuses. No Difficult to do with fuses. No Fuse selectivity tables.Fuse selectivity tables.Possible with CBsPossible with CBs

11

11

More TipsMore Tips

Tip #8Tip #8** -- Use SS Trips with LSUse SS Trips with LSI(0ff)I(0ff) or or FixedFixed Instantaneous Instantaneous OverrideOverrideTip #9Tip #9** –– Specify that SS Trip Units have Specify that SS Trip Units have adjustableadjustable::–– LTPU / LTDLTPU / LTD–– STPU / STD / I2TSTPU / STD / I2T–– INST(OFF) or Instantaneous Override INST(OFF) or Instantaneous Override (above (above

110% fault current at downstream device)110% fault current at downstream device)* * -- Do not forget the generator breakerDo not forget the generator breaker

Elevator Selective Coordination

Elevator Circuits must be selectively coordinated.

ELEV-2

CB-ELEV-2

23-ELEV ST

22-FDR ELEV-2

PNL-A - 250 A

ELEV-2 MOTOR

Tip #10 Tip #10 –– Elevator Elevator Circuit CoordinationCircuit Coordination

Feeder and Shunt Trip Devices, Feeder and Shunt Trip Devices, do not need to coordinate.do not need to coordinate.They feed the same load!They feed the same load!Impossible to do with fuses if Impossible to do with fuses if fuses are same size.fuses are same size.Impossible with CBsImpossible with CBs

Elevator Elevator Circuit Circuit

CoordinationCoordination

ELEV-1 ELEV-3

CB-ELEV-3CB-ELEV-1

SWBD

3-MSWBD MAIN

ELEV-1 MOTOR ELEV-3 MOTOR

28-ELEV 3 ST

27-FDR ELEV-3

30-ELEV 1 ST

29-FDR ELEV-1

11

11

22

22-GEN

23-GEN MAIN #1

GEN

SWBD-EMSB-1

24-FDR PNL F

PNL-F

Generator Generator CoordinationCoordination

Must Coordinate as Must Coordinate as wellwellGood News! Good News! -- Lower Lower Fault CurrentsFault CurrentsEasier to CoordinateEasier to Coordinate

11

22

GenGenPDCPDC

Decrement Decrement CurveCurveFault Current < Fault Current < Instantaneous Instantaneous SettingSetting

Series Rating of DevicesSeries Rating of Devices

Two or More Devices are Short Circuit Tested in Two or More Devices are Short Circuit Tested in SeriesSeriesCombinations can beCombinations can be–– Circuit BreakerCircuit Breaker–– FusesFuses–– Fuses and Circuit BreakersFuses and Circuit Breakers

Last device AIC (SC) Rating < AvailableLast device AIC (SC) Rating < AvailableAllAll Devices will operateDevices will operate

SWBD41638 Amps 3P

PNL-B36029 Amps 3P

25-Fdr Pnl-BInterruptingRating 65 kA

26-Lrgst BrnchInterruptingRating 25 kA

Series Rating Series Rating of Devicesof Devices

UL Listed UL Listed Combination is Combination is Series Rated 65 kASeries Rated 65 kANo Selective No Selective CoordinationCoordinationTip #11 Tip #11 –– Do Not Do Not Use Series Rated Use Series Rated DevicesDevices

11

11

Steps to Meet the CodeSteps to Meet the Code

Obtain Utility DataObtain Utility Data–– Maximum size of transformer (kVA)Maximum size of transformer (kVA)–– ImpedanceImpedance–– Winding ConnectionsWinding Connections–– Maximum available primary three phase and Maximum available primary three phase and

line to ground short circuit currentline to ground short circuit current


Model the distribution system in computerModel the distribution system in computerPerform Short Circuit StudyPerform Short Circuit StudyDetermine Equipment Full Load Ratings Determine Equipment Full Load Ratings (FLA)(FLA)


Determine protective device Determine protective device –– Standard Ampere Rating (NEC 240.6)Standard Ampere Rating (NEC 240.6)–– Short circuit interrupting rating (AIC)Short circuit interrupting rating (AIC)–– Downstream coordination current (DCC)Downstream coordination current (DCC)

Tip #12 Tip #12 –– Put the SC numbers on the One Put the SC numbers on the One Line DrawingLine Drawing

Steps to Meet the Code Steps to Meet the Code -- Circuit Circuit BreakersBreakers

Choose a device manufacturerChoose a device manufacturerUse NEC, DCC and Circuit Breaker Use NEC, DCC and Circuit Breaker Selection TableSelection TablePick circuit breakers with instantaneous Pick circuit breakers with instantaneous trips above the DCC.trips above the DCC.


Plot breaker curves toPlot breaker curves to–– Verify selective coordinationVerify selective coordination–– Determine device settingsDetermine device settingsFor new design projects For new design projects –– Repeat above steps for other manufacturesRepeat above steps for other manufactures–– Create Create detaileddetailed specifications for competitive specifications for competitive

biddingbidding–– Specify the Breaker Trip Unit Specify the Breaker Trip Unit Types (T/M or Types (T/M or

SS)SS) and and Instantaneous OverrideInstantaneous Override ValuesValues..


Tip #13 Tip #13 -- Add to Project Specifications:Add to Project Specifications:

“Where indicated on one line drawing, “Where indicated on one line drawing, breakers must have trip units with breakers must have trip units with Instantaneous setting or override ampere Instantaneous setting or override ampere rating 110% above the values shown on rating 110% above the values shown on one line drawing.”one line drawing.”

Steps to Meet the Code Steps to Meet the Code -- FusesFuses

Use Selectivity Ratio Guide to determine Use Selectivity Ratio Guide to determine fuse sizesfuse sizesVerify Verify Generator BreakerGenerator Breaker and and Downstream Downstream FusesFuses will coordinate.will coordinate.

517.17 Ground517.17 Ground--Fault Protection.Fault Protection.

(C) Selectivity. (C) Selectivity. –– GroundGround--fault protection for operation of the fault protection for operation of the

service service and and feederfeeder disconnecting means shall disconnecting means shall be fully be fully selectiveselective such that the feeder device, such that the feeder device, but not the service device, shall open on but not the service device, shall open on ground faults on the load side of the feeder ground faults on the load side of the feeder device. device.

GroundGround--Fault ProtectionFault Protection

Code Code RequiresRequires Ground Fault Selective Ground Fault Selective Coordination for Coordination for MainMain and and FeedersFeeders(medical facilities) only.(medical facilities) only.Code Code does notdoes not state that Ground Fault state that Ground Fault Protection Must Coordinate with the Phase Protection Must Coordinate with the Phase Protection.Protection.Considered a different protection schemeConsidered a different protection schemeMaximumMaximum PickupPickup setting is setting is 1,2001,200 AmperesAmperesMaximum Time DelayMaximum Time Delay setting is setting is 0.5 sec0.5 sec..

GroundGround--Fault ProtectionFault Protection

Limited Equipment options for fusesLimited Equipment options for fusesMany times impossible to prevent overlap Many times impossible to prevent overlap with ground fault and phase devices.with ground fault and phase devices.

More Problems with the CodeMore Problems with the Code

Modifications or additions to a facility. Modifications or additions to a facility. How far do you go to implement selective How far do you go to implement selective coordination?coordination?Small Transformers (15Small Transformers (15--45 kVA) and 45 kVA) and PanelboardsPanelboards

More Problems More Problems with the Codewith the Code

Hospital Isolation Hospital Isolation PanelboardsPanelboards

Tools for Breaker CoordinationTools for Breaker Coordination

Square D Square D –––– Enhancing Short Circuit Selective Coordination Enhancing Short Circuit Selective Coordination

with Low Voltage Breakerswith Low Voltage Breakers

New Products coming down the pipe! New Products coming down the pipe! Eaton Electric Eaton Electric –––– Breaker Selectivity ChartBreaker Selectivity Chart–– Breaker Coordination Excel SpreadsheetBreaker Coordination Excel Spreadsheet

101010104.2150

101010104.24.2125

101010105.04.22.52.2100

101010105.04.22.52.290

101010105.04.22.52.280

101010105.04.22.52.270

101010106.04.22.52.20.860

101010106.04.22.52.20.850

101010106.04.23.42.20.840

101010108.05.03.42.21.230

101010108.05.03.42.21.220

101010101010.04.02.21.215

BR, BAB, HQP & QC

(10 kA)

R (2500 A)

N (1200 A)

LG (630A)

L(600 A)

K (400 A)

J (250 A)

JG(250 A)

F (225 A)

EG(125 A)Rating

Upstream (Main) MCCBDownstream (Branch) CB

All Values (Typical) in RMS Current Levels @ 240, 415 / 480 Vac

Coordination Table.

Job Title

Company Name

Available Fault Current CalculationEnter Available Utility Fault Current Amperes

If not known, enter transformer KVA rating 300 KVAEnter transformer impedance (Z) 5 %

Select Primary System VoltageSelect Secondary System Voltage

Transformer Calculations Primary Voltage 480 VoltsPrimary Current 361 AmperesMaximum Primary Protection per NEC 450.3(B) 902 AmperesRecommended Primary Breaker Rating 1000 Amperes

Secondary Voltage 208 VoltsSecondary Current 833 AmperesMaximum Secondary Protection per NEC 450.3(B) 1041 AmperesRecommended Secondary Breaker Rating 1200 Amperes

ISCA = Transformer FLA x 100 16,655 AmperesTransformer %Z

Short Circuit Current (RMS symmeterical) 16,655 Amperes@ Transformer Terminals

Motor Contributions 1,665 Amperes

Total Short Circuit Current 18,320 Amperes(Transformer/Utility+Motor Contribution)

Three Phase 208Y/120

Three Phase 480

Select Conductor Data Between Main MCCB and Branch MCCBSelect Conductor Type & Raceway Charisteristics

Select Conductor Size

Enter Conductor Length 100 Feet

Enter Number of Conductors / Phase 1

Fault Current @ Load Terminals of Branch MCCB 7,815 Amperes

Select Transformer Secondary MCCB

Select Downstream Branch MCCB

Coordination Level 2,300 Amperes

Results Select Larger Frame Size

Copper in Metalic Raceway

250 kcmil

JG(250 A)

F 100A

Circuit Breaker Selection TableCircuit Breaker Selection Table

Table Used to Quickly Select Breakers that Table Used to Quickly Select Breakers that maymaycoordinate.coordinate.Easily Sorted in Excel.Easily Sorted in Excel.

Circuit Breaker Selection TableCircuit Breaker Selection Table

Example 1Example 1Determine the Determine the –– SWBD Main (4000 Amp)SWBD Main (4000 Amp)–– Feeder to ATS (200 Amp)Feeder to ATS (200 Amp)–– Panelboard Main (200 Amp)Panelboard Main (200 Amp)–– Largest Feeder is 70A KH Largest Feeder is 70A KH

AMPAMP

32-MSWBD MAIN

SWBD41638 Amps 3P41081 Amps SLG12-Fdr ATS-E

12-PNL-A MAIN

PNL-A - 250 A30933 Amps 3P27901 Amps SLG

E N

ATS 260 Amp

76-Lrgst Brnch

32-MSWBD MAINSQUARE D NW40H Sensor/Trip 4000 ASettings Phase LTPU/LTD (A 0.4-1.0 x S) 1 (4000A); 0.5 STPU (1.5-10 x LTPU) 5 (20000A) STD (INST-0.4) 0.3(I^2 T Out) INST (2-15 x S) 15 (60000A)

12-Fdr ATS-ESQUARE D NT08H Sensor/Trip 400 ASettings Phase LTPU/LTD (A 0.4-1.0 x S) 0.5 (200A); 24 STPU (1.5-10 x LTPU) 6 (1200A) STD (INST-0.4) 0.2(I^2 T Out) INST Override Fixed (40000A)

Example 1Example 1

12-PNL-A MAINSQUARE D NT08H Sensor/Trip 400 ASettings Phase LTPU/LTD (A 0.4-1.0 x S) 0.5 (200A); 16 STPU (1.5-10 x LTPU) 5 (1000A) STD (INST-0.4) 0.1(I^2 T Out) INST Override Fixed (40000A)

76-Lrgst BrnchSQUARE D KH Sensor/Trip 70 ASettings Phase Thermal Curve (Fixed) INST (5-10 x Trip) 10.0 (700A)

Example 1Example 1

Example 1Example 1Determine Determine the the –– SWBD Main SWBD Main --–– Feeder to Feeder to

ATSATS–– PNLBD MainPNLBD Main–– Largest Largest

Feeder is Feeder is 70A KH AMP70A KH AMP

Example 2Example 2Determine the Determine the –– Panel A FeederPanel A Feeder–– Panel C MainPanel C Main–– Panel C Largest Feeder is 20A QOPanel C Largest Feeder is 20A QO

Step 1 Step 1 –– Determine 208 V Fault Determine 208 V Fault in 480 V amperes.in 480 V amperes.3,094 X 208/480 = 1,341 A3,094 X 208/480 = 1,341 A

Example 2Example 2

Pick 125 Amp Feeder Breaker TPick 125 Amp Feeder Breaker T--3 3 –– Instantaneous OR > 1,341Instantaneous OR > 1,341–– 1,341 / 125 = 10.7 (Can not use T/M)1,341 / 125 = 10.7 (Can not use T/M)–– Must Use SS TripMust Use SS Trip

Pick Panel C 100 Ampere MainPick Panel C 100 Ampere Main–– Must Coordinate with Largest Branch BreakerMust Coordinate with Largest Branch Breaker

Example 2Example 213-Pnl C MAINSQUARE D PG Sensor/Trip 250 ASettings Phase LTPU/LTD (A 0.4-1.0 x S) 0.4 (100A) STPU (1.5-10 x LTPU) 10 (1000A) STD (0-0.4) 0.1(I^2 T In) INST Override Fixed (24000A)

17-Lrgst BrnchSQUARE D QO3 Sensor/Trip 20 ASettings Phase Fixed

12-PNL-A MAINSQUARE D NT08H Sensor/Trip 400 ASettings Phase LTPU/LTD (A 0.4-1.0 x S) 0.5 (200A); 16 STPU (1.5-10 x LTPU) 5 (1000A) STD (INST-0.4) 0.2(I^2 T Out) INST Override Fixed (40000A)

14-Fdr to T-3SQUARE D LE Sensor/Trip 250 APlug 250 ASettings Phase LTPU (0.5-1.0 x P) 0.5 (125A) LTD (2-14 Sec.) 2 STPU (2-8 x P) 2.5 (625A) STD (0.1-0.5 Sec.) 0.1(I^2 T Out) INST (2.5-8 x P) 8.0 (2000A)

Example 2Example 2

Example 2Example 2

SummarySummary

You must change the way you design You must change the way you design circuits for:circuits for:–– Emergency Emergency –– StandbyStandby–– ElevatorElevatorManufacturers must provide:Manufacturers must provide:–– New Equipment to meet the codeNew Equipment to meet the code–– Tools (tables, spreadsheets, charts)Tools (tables, spreadsheets, charts)–– II22T Withstand curves for EquipmentT Withstand curves for Equipment

Need more InformationNeed more Informationwww.powerstudies.comwww.powerstudies.com–– ArticlesArticles–– LinksLinks–– Specifications for Power System StudiesSpecifications for Power System Studies

Short CircuitShort CircuitProtective Device CoordinationProtective Device CoordinationArc Flash HazardArc Flash Hazard

Questions??Questions??

Thank you for your Thank you for your time! time!

Who are we? Who are we? Electrical Electrical Engineering Engineering Consulting FirmConsulting FirmWe Specialize in We Specialize in performing Power performing Power System StudiesSystem Studies90% of our 90% of our business is in business is in performing Power performing Power System StudiesSystem Studies

Where are we located?Where are we located?Our office is located in Covington, WA.Our office is located in Covington, WA.Near SeattleNear SeattleOur territory is Western third of USOur territory is Western third of USWe have also done studies for clients in We have also done studies for clients in Russia and South AmericaRussia and South America

meeting nec for selective coordination

Documents