cutler-hammer high resistance grounding

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CA08104001E For more information visit: www.cutler-hammer.eaton.com PIN 0190500, 0220300, 0190501

January 2003

Contents

Resistance Grounding System37

Ref. No. 1325

R e s i s t a n c

e

G r o u n d

i n g S

y s t e m

Description Page

Resistance Grounding System

High Resistance Grounding System — Medium Voltage . . . . . . . . . . . . . 37.1-1

High Resistance Grounding System — Low Voltage . . . . . . . . . . . . . . . . 37.2-1

Neutral Grounding Resistors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37.3-1

Specifications

For complete product specifications in CSI format seeEaton’s Cutler-Hammer Product Specification Guide

High Resistance Grounding System — Medium Voltage . . . . . . Section 16451A

High Resistance Grounding System — Low Voltage . . . . . . . . . Section 16451B

Neutral Grounding Resistors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . Section 16391

C-HRG Free-Standing NEMA 1 Enclosure

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Ref. No. 1326

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37January 2003

Resistance Grounding SystemHigh Resistance Grounding System — Medium Voltage

General DescriptionRef. No. 1327

Medium Voltage HighResistance Grounding System

C-HRG Free-Standing NEMA 1 Unit

Product DescriptionWhere continuity of service is a highpriority, high resistance grounding canadd the safety of a grounded systemwhile minimizing the risk of serviceinterruptions due to grounds. Theconcept is a simple one: providea path for ground current via agrounding transformer (with adjust-able resistance across its secondary)that limits the current magnitudeand a monitor to determine whenan abnormal condition exists.

The ground current path is providedat the point where the service begins,by placing a predominantly resistiveimpedance in the connection fromsystem neutral to ground. Controlequipment continuously measuresground current; a relay detects whenthe current exceeds a predeterminedlevel. An alarm alerts building person-nel that a ground exists. The system

has built-in fault tracing means to assistin finding the source of the ground.A 120V AC supply (remote) is requiredfor control power for the system.

Figure 37.1-1.HRG —High Resistance Grounding System

Application IssuesThis new member of Eaton’s Cutler-Hammer MV Metal-Clad Switchgearfamily has actually been around formany years. However, it is now offeredas a stand-alone unit that can beadded to existing installations. TheC-HRG is utilized to protect an electri-cal distribution system from damagingtransient overvoltages caused by

ground faults. It also provides a meansto locate the ground fault, thereforeextending the life of the distributionsystem.

Ratings and Configurations

The C-HRG MV is offered at the 5 kVclass rating. It can be applied to deltaor wye ungrouped 3-wire distributionsystems. Standard dimensions are36-inch (914.4 mm) W x 40-inch (1016.0mm) D x 92-inch (2336.8 mm) H.

4200V (Maximum) Delta Systems

To add high resistance groundingto an ungrounded delta-connectedsystem, a neutral point must be cre-ated. Three single-phase transformerscan be interconnected in a wye-brokendelta configuration to provide such aneutral point. The transformers andgrounding resistors are chosen to limitthe ground current to a maximum

value of 6 amperes.

Application Note:The neutral point maynot be used to serve phase-to-neutral loads.Also, this technique may be applied on wye-connected sources when the neutral pointis not conveniently accessible from theservice entrance location. This method isshown in the illustration above. One deltahigh-resistance grounding would groundthe 5 kV system.

HRG = High-ResistanceGrounding System

Wye HRG

51N

59

DeltaHRG

59

51

Generator

BusDuct

BusDuct

To Power Circuit

Conduit

5 kV Switchgear

To MCC

Cable

BusDuct

Wye HRG

51N

59

Utility

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7.1-2


January 2003


7

High Resistance Grounding System — Medium Voltage


4200V (Maximum) Wye Systems

To add high resistance grounding toa wye-connected system, resistorsare placed across the secondaryof a grounding transformer whoseprimary is placed in series with the

neutral-to-ground connection of thepower source. The resistors arechosen to limit the current to amaximum value of 6 amperes.

Application Note:Per 1999 NEC 250-36(4),line-to-neutral loads may not be connectedto a system in which the neutral is resis-tance-grounded. Also, if the system hastwo switchable sources not permanentlyconnected to the bus, two wye-typegrounding systems are required asshown in Figure 37.1-1.

Ground Current Detection

Any time a system is energized,a small ground current called the

“capacitive charging current” willbe observed. For medium voltage(4200V and below) systems, thisnaturally occurring current is typically3A or less.

When one phase becomes grounded,additional current above the charginglevel will flow. As all ground currentmust flow through the groundingresistor/grounding transformerassembly, an ammeter in this circuitwill read the total amount of groundcurrent. By placing a current-sensingrelay in series with the ammeter, thecurrent relay can be adjusted to pick-up at a level in excess of the capacitive

charging current, thus indicating theabnormal condition.

Alternatively, an optional voltmeter-relay can be connected across thegrounding resistors. The voltageacross the resistors is proportionalto the amount of ground current. Thevoltmeter-relay’s pickup adjustmentis set above the capacitive chargingcurrent, to the desired detection level.

In both current and voltage detectionmethods, the ground current ammeterprovides a direct reading of the totalactual ground current present in thesystem at that time. It will be helpfulto periodically note the ammeter’sreading: a trend toward higher valuesmay indicate the need for equipmentmaintenance, and hence reduce theoccurrence of unplanned shutdowns.

Indication and Alarm Circuits

When a fault is detected, an adjustabletime delay is provided to overridetransients. When the time delay hasbeen exceeded, the green “normal”light will turn off, the red “ground

fault” light will turn on, and theground alarm contacts will transfer.If equipped with the optional alarmhorn, it will sound.

The grounding transformer secondarybreaker must be closed for the systemto be operational. Should this breakerbe opened at any time, the system willsignal a ground fault condition as afail-safe feature. The breaker must beclosed to clear the alarm signal.

When the fault is cleared, the current/ voltage relay will reset. If the resetcontrol is set on “auto,” the lights willreturn to “normal” on, “ground fault”

off, and the ground alarm contacts willre-transfer. If the reset control is set on“manual,” the lights and relay con-tacts will remain latched until theoperator turns the reset control to“reset.” The lights and ground alarmcontacts will then return to normal.The system can be reset only if thefault has been cleared.

During a fault, the optional alarmhorn can be silenced at any time byusing the “alarm silence” pushbutton.It will not re-sound until either thesystem is reset, or the re-alarm timerexpires. The re-alarm timer is activatedby the “alarm silence” control. If thehorn has been silenced but the faulthas not been cleared, the timer willrun. It has a range of 2 – 48 hours.When the timer times out, the hornwill re-sound, alerting maintenancepersonnel that the fault has notbeen cleared.

Test Circuit

A test circuit is provided to allow theuser to quickly determine that thesystem is working properly. The testcircuit will operate only under normalconditions — it will not allow testing if the system is sensing a fault. The testoperation does not simulate an actualsystem ground fault. It does, however,test the complete controls of the faultindication and pulsing circuitry. Thesystem then reacts as it would underactual system ground conditions —lights transfer, alarm contacts transferand the (optional) horn sounds.

Pulser Circuit

The pulser circuit offers a convenientmeans to locate the faulted feeder andtrace the fault to its origin. The pulseris available any time a fault has beendetected. The pulse intervals are con-

trolled by an adjustable recycle timer.The “pulse” light flashes on and off,corresponding to the on-off cycles of the pulser contactor. The pulser con-tactor switches a bank of resistors onand off, thus allowing a momentaryincrease in the ground current(approximately a 4A current pulseabove the ground current).

Locating a Ground Fault

The current pulses can be noted with aclamp-on ammeter when the ammeteris placed around the cables or conduitfeeding the fault. The operator testseach conduit or set of cables until the

pulsing current is noted. By movingthe ammeter along the conduit, orchecking the conduit periodicallyalong its length, the fault can be tracedto its origin. The fault may be locatedat the point where the pulsing currentdrops off or stops.

If little or no change in the pulsingcurrent is noted along the entire lengthof a conduit, then the fault may be inthe connected load. If the load is apanelboard, distribution switchboardor motor control center, repeat theprocess of checking all outgoing cablegroups and conduits to find the faultedfeeder. If the fault is not found in an

outgoing feeder, the fault may beinternal to that equipment.

Application Note:It may not be possibleto precisely locate faults within a conduit.The ground current may divide into manycomponents, depending on the number of cables per phase, number of conduits perfeeder, and the number and resistance of each ground point along the conduits. Theresulting currents may be too small to allowdetection or may take a path that the am-meter cannot trace. An important note tokeep in mind is that while the pulser cangreatly aid in locating a fault, there may becertain conditions under which the pulsescannot be readily traced, and other testprocedures (megohm, high-potential, etc.)

may be needed.

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37January 2003



Sequence of Operations

Normal

s Green “normal” light on.

s Red “ground fault” light off.

s White “pulse” light off.

s System control switch in“normal” position.

s Reset control switch in either“auto” or “manual.”

Test

Turn and hold the system controlswitch in the “test” position. Thismode will test the control circuitryonly. It will bypass the sensing circuitand cause the green “normal” lightto turn off and the red “ground fault”light to turn on. The pulser will beactivated as well. The white “pulse”light will turn on and off as the pulsercontactor closes and opens. However,

the ground current ammeter will notdisplay the total ground current,including the incremental pulse cur-rent. When ready, return the systemcontrol switch to “normal.” The pulserwill stop. If the reset control is in the“manual” position, turn it to “reset” toreset the fault sensing circuit. The red“ground fault” light will turn off, andthe green “normal” light will turn on.Test mode is not available if the sys-tem is detecting a ground. The sensingcircuit will disable the test circuit.

Ground Fault

When the sensing circuit detects a fault,

the green “normal” light will turn off and the red “ground fault” light willturn on. The ground current ammeterwill indicate the total ground current.To use the pulser, turn the systemcontrol switch to “pulse.” The pulsercontactor will cycle on and off as con-trolled by the recycle timer relay. Usethe clamp-on ammeter to locate thefaulted feeder. Open the feeder andclear the fault. If the reset control switchis in the “manual” position, turn itto “reset” to reset the sensing circuit.(If reset control is in “auto,” it will resetitself.) When ready to restore serviceto the load, close the feeder. Return

the system control to “normal.”

Product FeaturesWhen a ground fault occurs on anungrounded system, high transient volt-ages can occur, which may cause morefrequent equipment failures than if theequipment were grounded. These tran-

sient overvoltages, as high as four timesthe normal voltage, reduce the life of thesystem’s insulation resulting in:

s Motor failure.

s Transformer failure.

s Coil failure.

s Electronic equipment failure.

s Cable insulation failure.

By utilizing a high resistance groundsystem, many facilities can gain thebenefit of a grounded system withoutimpairing the continuity of service totheir equipment. The concept behindhigh resistance grounding is to pro-

vide a path for the ground current toflow while limiting its magnitude byusing a resistor. The ground currentpath is provided at the point whereservice begins. Control equipmentcontinuously monitors the magnitudeof the ground current. When theground current exceeds a predeter-mined level, the built-in alarm relayalerts building personnel that a groundfault exists. In addition, the C-HRG MV“Safe Ground” System has a built-infault pulsing as a means to assist infinding the source of the ground faultwithout interrupting service.

C-HRG Unit Shown with the Door Open

s Current sensing ground faultdetection (2 – 10 amperes pickup/ 0.5 – 20 second delay).

s Ground current transformer(10/10 ratio).

s Control circuit pull fuseblock.

s Ground current ammeter(0 – 10 amperes, 1% accuracy).

s Indicating lightsRed (ground fault)Green (normal)White (pulse).

s Adjustable pulsing timer(0 – 10 seconds).

s Tapped resistors (limits primarycurrent to 3 – 6 amperes).

s 3-position selector switch(normal, pulse, test).

s Control switch for manualor automatic reset.

s Ground fault contacts (1NO/1NC).

s Shorting terminal block for groundcurrent CT.

s UL label.

s Wiremarkers.

The system is completely assembled,wired and tested at the factory inaccordance with NEMA and UL requirements. A certified productiontest report is shipped with the unit.

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7.1-4


January 2003


7


Technical DataRef. No. 1330

Technical Data — Circuit Diagrams

Figure 37.1-2.Ungrounded Wye System(with standard current and optional voltage relay fault detectors)

Figure 37.1-3.Ungrounded Delta System(with standard current and optional voltage relay fault detectors)

Detector

Current D e

t e c

t o r

V o

l t a g e

M e c

h a n

i c a

l

H3

H2H1

X3

X2

X1X0

UngroundedWye

ToDistributionCircuits

X0

5 kV - CLEFuses

I n t e r l o c

k

[ 1 ]ControlPower

Transformer

SecondaryCircuitBreakerB B

59

ShortCircuitT.B.

AM

5IN

C T

1 0 / 1 0 A

P u

l s i n g

R e s

i s t o r

P u

l s i n g

C o n

t a c

t o r

G r o u n

d i n g

R e s

i s t o r

GroundCurrentAdjustmentT.B.

ToRemoteAlarm

G R W

ControlCircuit

Normal Alarm Pulsing AudibleAlarm

Optional

20A

20A

Fuses 120V60 HzSupply

O p

t i o n a

l

C

3A

4A

5A

6A

4

Option

Current

Detector D e

t e c

t o r

V o

l t a g e

H3

M e c

h a n

i c a

l

H2H1

UngroundedDelta

ToDistributionCircuits

5 kV - CLEFuses

I n t e r l o c

k

3-AuxiliaryControlPower

Transformers

SecondaryCircuitBreaker

B B

59

Short CircuitT.B.

AM

5IN

C T

1 0 / 1 0 A

P u

l s i n g

R e s

i s t o r

P u

l s i n g

C o n

t a c

t o r

G r o u n

d i n g

R e s

i s t o r

GroundCurrentAdjustmentT.B.

ToRemoteAlarm

G R W

ControlCircuit

Normal Alarm Pulsing AudibleAlarm

Optional

20A

20A

Fuses 120V60 HzSupply

O p

t i o n a

l

C

3A

4A

5A

6A

4

X3

X2X1

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37January 2003


DimensionsRef. No. 1331

Dimensions in Inches (mm)

Figure 37.1-4.NEMA 1 Free-Standing

Primary ConduitEntrance

Vent

92.00

(2336.8)

36.00

(914.4)

36.00

(914.4)

40.00

(1016)

3.50

(88.9)

8.50

(215.9)

1.50

(38.1)

3.76

(95.6)

3.62

(91.9)

3.25

(82.6)

7.12

(180.9)

9.38

(238.3)

3.50

(88.9)

3.75

(95.3)

3.00

(76.2)

2.75

(69.9)

1.75

(44.5)

.81

(20.6).562 (14.3) Diameter (4)

Primary ConduitEntrance

Secondary ConduitEntrance

2.00 (50.8) DiameterKnockoutf or SecondaryConduit Entrance

Plan View

Front View

Floor Plan

3.75

(95.3)

3.75

(95.3)

2.75

(69.9)

2.75

(69.9)

.81

(20.6)

2.75

(69.9)

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7.1-6


January 2003


7


Technical Data — High Resistance Pulsing Grounding SystemsRef. No. 1332

Product SelectionEaton’s Cutler-Hammer C-HRG High Resistance Grounding Assembly can be completely described by an 8-digitcatalog number: MVRG-_ _ _ _ _ _ _ _

Table 37.1-1.High Resistance Pulsing Grounding Systems Catalog Numbering System

Example: MVRG-FWWCLLTS defines a free-standing NEMA 1 enclosure, 4200V/60 Hz, Wye-connected system, current-sensingcontrol scheme, alarm horn with re-alarm timer, alarm relay with 1NO and 1NC, transformer type incandescent lights,wrap-on wiremarkers.

MVRG F W W C L L T S

Enclosure Type

Free-standing enclosure formounting grounding transformerand resistors internally.

F = Free-standing NEMA 1R = Free-standing NEMA 3R outdoor

Service Voltage

W = 4200 V 60 HzX = 2400 V 60 HzY = 3300 V 60 Hz

System Neutral Point

Choose Wye when the neutralpoint of the power source isaccessible for direct connectionto grounding transformer.Choose Delta when there is noneutral or when neutral is notaccessible.

W = WyeD = D (Wye broken Delta

grounding transformer)

Fault Sensing

Current SensingVoltage SensingVoltage Sensing

C = Overcurrent relayV = Single set-point

voltmeter relayD = Indicating voltmeter only

Audible Alarm

Alarm contactsare standard onall assemblies.

N = No audible alarmL = Alarm horn with

re-alarm timer

Loss of ControlPower Alarm

A relay is connectedacross the customer’s120V AC supply.

N = No relayL = Alarm relay with

1 NO and 1 NC

Indicating Lamps

Standard lights are industrial,oil-tight, transformer type.Optional are the same typelights except with a push-to-test feature.

T = Transformer typeincandescent lamps

X = Push-to-testtransformer type

Wiremarkers

Marks all internal wiringfor ease of maintenance.

S = Standard wrap-onT = Tube/heat shrink type

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37January 2003

Resistance Grounding SystemHigh Resistance Grounding System — Low Voltage


Low Voltage High ResistanceGrounding System

Where continuity of service is a highpriority, high resistance groundingcan add the safety of a grounded

system while minimizing the risk of service interruptions due to grounds.The concept is a simple one: providea path for ground current via a resis-tance that limits the current magni-tude, and monitor to determine whenan abnormal condition exists. Thisprovides for maximum continuityof service, since no tripping occurs forthe resistance limited ground fault.

The ground current path is providedat the point where the service begins,by placing resistance in the connectionfrom system neutral to ground. Controlequipment continuously measures

ground current; a relay detects whenthe current exceeds a predeterminedlevel. An alarm alerts building person-nel that a ground exists. The systemhas built-in fault tracing means to assistin finding the source of the ground.An integral transformer provides con-trol power from the primary source.

Standard Features

s Current sensing ground faultdetection (1 – 5 ampere pickup/ 0.5 – 20 seconds delay).

s Ground current transformer(10/10 ratio).

s Control circuit disconnect switch(fused).

s Lockable door handle.

s PLC controller.

s Operator interface panel with:

u Ground fault indication

u Normal indication

u Pulse operation indication

u Normal, Test and Pulse initiation

u Manual or automatic reset

s Adjustable pulsing timer circuit.

s Tapped Resistors (1 – 5 amperes).

s Ground fault contact.

s Shorting terminal block for groundcurrent transformer.

s UL label.

s Rated for use up to 200 kA faultcurrent system.

s Front accessible.

s Sleeve type wiremarkers.

s Three “zig-zag” or “wye-brokendelta” grounding transformers forsystems without a neutral point.

C-HRG Free-Standing NEMA 1 Unit

C-HRG Wall Mounted Unit (Separately Mounted Resistors Not Shown)

Figure 37.2-1.Typical Distribution Systemᕃ Phase-to-neutral loads require a delta-wye distribution transformer. The neutral on the secondary

side of this transformer must be solidly grounded.

Bus Duct

Main Breaker

600V (Max.)

HV

C-HRGHigh-Resistance

GroundingSystem

Source

DS-VSRMotorStarter

Conduit

200 Hp

Motor Loads

M M M

MCC

FeederBreaker

FeederBreaker

Cable Tray

DistributionSwitchboard

Misc. 3WLoads

FeederBreaker

Conduit

Transformer

3W or 4WPanel-Board

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7.2-2


January 2003


7

High Resistance Grounding System — Low Voltage


600/347V (Maximum) Wye SystemsTo add high resistance grounding toa wye-connected system, resistorsare placed in series with the neutral-to-ground connection of the powersource. The resistors are chosen to

limit the current to a maximum valueof 5 amperes.

Application Note:Per 1999 NEC 250-36(4),line-to-neutral loads may not be connectedto a system where the system is resistance-grounded.

600V (Maximum) Delta SystemsTo add high resistance grounding toan ungrounded delta-connected sys-tem, a neutral point must be created.Three single-phase transformers canbe interconnected in a zig-zag or Wye-broken delta configuration to providesuch a neutral point. The transformers

and grounding resistors are chosen tolimit the ground current to a maximumvalue of 5 amperes.

Application Note:The neutral point maynot be used to serve phase-to-neutral loads.Also, this technique may be applied on wye-connected sources when the neutral pointis not conveniently accessible from theservice entrance location.

Ground Current DetectionAny time a system is energized, a smallground current called the “capacitivecharging current” will be observed.For low voltage (600V and below)systems, this naturally occurring

current is typically 1 ampere or less.

When one phase becomes grounded,additional current above the charginglevel will flow. As all ground currentmust flow through the groundingresistor/grounding transformer assem-bly, the operator interface panel willdisplay the total amount of groundcurrent. By placing a current-sensingrelay in this circuit, the current relaycan be adjusted to pick up at a levelin excess of the capacitive chargingcurrent, thus indicating the abnormalcondition.

The operator interface panel providesa direct reading of the total, actualground current present in the systemat that time. It will be helpful toperiodically note this reading; a trendtowards higher values may indicatethe need for equipment maintenanceand hence reduce the occurrence of unplanned shutdowns.

Indication and Alarm CircuitsWhen a fault is detected, an adjustabletime delay is provided to override tran-sients. When the time delay has beenexceeded the green “normal” light willturn off, the red “ground fault” light

will turn on, and the ground alarmcontacts will transfer. If equipped withthe optional alarm horn, it will sound.

When the fault is cleared, the circuitwill reset. If the reset control is set on“auto,” the operator interface panelwill indicate “normal” on, “groundfault” indication will go off, and theground alarm contacts will re-transfer.If the reset control is set on “manual,”the indications and relay will remainlatched until the operator turns thereset control to “reset.” The indicationsand ground alarm contacts will thenreturn to normal. The system can be

reset only if the fault has been cleared.During a fault, the optional alarm horncan be silenced at any time by usingthe “alarm silence” function of theoperation interface panel. It will notre-sound until either the system isreset, or the re-alarm timer expires.The re-alarm timer is activated by the“alarm silence” control. If the hornhas been silenced but the fault hasnot been cleared, the timer will run.It has a range of 2 – 48 hours. Whenthe timer times out, the horn willre-sound, alerting maintenancepersonnel that the fault has notbeen cleared.

Test CircuitA test circuit Is provided to allowthe user to quickly determine that thesystem is working properly. The testcircuit will operate only under normalconditions — it will not allow testing if the system is sensing a fault. A sepa-rate grounding resistor is provided,connected to a relay operated by the“test” function of the operator inter-face panel. The relay’s contact groundsphase B through the test resistor, caus-ing ground current to flow. The systemthen reacts as it would under actual

system ground conditions — indica-tions transfer, alarm contacts transferand the (optional) horn sounds.

Pulser CircuitThe pulser circuit offers a convenientmeans to locate the faulted feederand trace the fault to its origin. Thepulser is available any time a faulthas been detected. The pulse intervals

are controlled by an adjustable recycletimer. The “pulse” indication on theoperator interface panel flashes on andoff, corresponding to the on-off cyclesof the pulser contactor. The pulsercontactor switches a bank of resistorson and off, thus allowing a momentaryincrease in the ground current(approximately a 5 ampere currentpulse above the ground current).

Locating a Ground FaultThe current pulses can be noted with aclamp-on ammeter when the ammeteris placed around the cables or conduitfeeding the fault. The operator testseach conduit or set of cables until thepulsing current is noted. By movingthe ammeter along the conduit, orchecking the conduit periodicallyalong its length, the fault can be tracedto its origin. The fault may be locatedat the point where the pulsing currentdrops off or stops.

If little or no change in the pulsingcurrent is noted along the entire lengthof a conduit, then the fault may bein the connected load. If the load is apanelboard, distribution switchboardor motor control center, repeat theprocess of checking all outgoing cable

groups and conduits to find the faultedfeeder. If the fault is not found in anoutgoing feeder, the fault may beinternal to that equipment.

Application Note:It may not be possibleto precisely locate faults within a conduit.The ground current may divide into manycomponents, depending on the number of cables per phase, number of conduits perfeeder, and the number and resistance of each ground point along the conduits. Theresulting currents may be too small to allowdetection or may take a path that the amme-ter cannot trace. An important note to keepin mind is that while the pulser can greatlyaid in locating a fault, there may be certainconditions under which the pulses cannot

be readily traced, and other test procedures(meg-ohm, high-potential, etc.) maybe needed.

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37January 2003



Sequence of Operations

Normal

s Green “normal” indication on.

s Red “ground fault” indication off.

s White “pulse” indication off.

s System control in “normal” position.

s Reset control in either “auto” or“manual.”

Test

Initiate the test mode through theoperator interface panel. Phase Bwill be grounded via the test resistor.The ground-current will activate thesensing circuit, causing the green“normal” indication to turn off and thered “ground fault” indication to turnon. The pulser will be activated aswell. The white “pulse” indication willturn on and off as the pulser contactorcloses and opens. The operator inter-face panel will display the total groundcurrent, including the incrementalpulse current. When ready, return thesystem control switch to “normal.”The pulser will stop. If the reset control

is in the “manual” position, turn itto “reset” to reset the fault sensingcircuit. The red “ground fault” indica-tion will turn off, and the green“normal” indication will turn on.Test mode is not available if the sys-tem is detecting a ground. The sensingcircuit will disable the test circuit.

Ground Fault

When the sensing circuit detects a fault,the green ”normal” indication will turnoff and the red “ground fault” indicationwill turn on. The operator interface panelwill indicate the total ground current.To use the pulser, initiate the pulse cyclethrough the operator interface panel.The pulser contactor will cycle on and off as controlled by the recycle timer relay.Use the clamp-on ammeter to locatethe faulted feeder. Open the feeder andclear the fault. If the reset control is inthe “manual” position, initiate the resetfunction to reset the sensing circuit.(If reset control is in “auto,” it will resetitself.) When ready to restore serviceto the load, close the feeder. Return thesystem control to “normal.”

Figure 37.2-2.Front Door Layout

ENTER

SELECT

NO

16 Characters XX

16 Characters XX

Micro PanelMate

DB20

YES

The system neutral conductor shall notbe

connected to ground at the switchboard or

at the source (utility orgenerator) except

through thegrounding impedance.

CurrentRatings:

Rated Time:

5A Ground CurrentMax.

5A Pulsing CurrentMax.ContinuousDuty at

Rated Current

High Resistance Grounding System Ratings

GroundAlarm

Construction Features1. Tapped resistors supply ground

current between 1 and 5 amperesin 1 ampere increments.

2. Pulse current is an additional

5 amperes. (Pulse currents of alower magnitude may be difficultto detect.)

3. Pulse timer is adjustable from3 to 60 pulses per minute.

4. Time delay for current sensingrelay is 0.5 to 20 seconds witha 1 to 5 ampere pickup. (Timedelay for voltage sensing relayis 1 to 60 seconds.)

5. Fused disconnects are supplied forcontrol and ground transformers.

6. All door mounted equipment isguarded against accidental contact.

7. All exterior nameplates are fas-tened with stainless steel screws.

8. Nameplates are 2-ply with 3/16-inch (4.8 mm) lettering. The name-plate size is 1-inch x 2-1/2 inches(25.4 x 63.5 mm) white backgroundwith black lettering is standard.

9. Top and bottom cable entry areasare standard.

10. Phase and neutral terminalsaccept #12 AWG to #8 AWG.

11. Ground terminal accepts wiresizes from #8 AWG to 500 kcmil.

Ground bus is 1/4-inch x 2 inches(6.4 x 50.8 mm) copper.

12. The paint is applied using anelectrostatic powder coatingsystem. The standard color isANSI 61, light gray.

13. Line side fuses are rated for useup to 200 kA fault current systems.All other fuses are rated to protecteach circuit as required.

14. The resistors are wire wound ona steel tube, insulated by Micarta.Resistors are mounted on a steelrack with ceramic insulators.

15. No. 8 AWG wire is used for internalconnections from the neutral pointto ground. Control connectionsare a minimum of #14 gauge. Allcontrol wires insulation is type SIS.

16. UL listed.

17. A list of recommended spare partscan be provided after the finalengineering is complete.

18. Steel pocket on the inside of thedoor is provided to hold drawingsand manuals.

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7.2-4


January 2003


7

High Resistance Grounding System — Low Voltage


Technical Data

Figure 37.2-3.4-Wire Source — Fault Detection via Current Relay



HV

To

Distribution

Equipment

600/347V (Max) Wye, Ungrounded

A B C

G

N

PulserResistor

G R W

GroundingResistor

Circuit

Control

TestResistor

CLF

CLF

CLF

PLC 51N

HV 600V (Max) Delta, Ungrounded

A B C

G

G R W

CircuitControl

CLF

GroundingTransf ormers

Zig-ZagCLF

CLF

ToDistributionEquipment

PulserResistor

GroundingResistor

stResistor

PLC 51N

HV 600V (Max) Delta, Ungrounded

A B C

G

G R W

Circuit

ControlCLF

CLF

CLF

PulserResistorGrounding

Transf ormers

Wye -

ToDistribution

Equipment

GroundingResistor

T stResistor

PLC 51N

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37January 2003


Layout — DimensionsRef. No. 1337

Figure 37.2-6.NEMA 1 Free Standing Figure 37.2-7.NEMA 3R Outdoor

Figure 37.2-8.NEMA 1 Wall Mounted

.56 (14.2) Dia. (4)

5 x 5 (127.0 x 127.0)

Conduit Entry Area

(Top and Bottom)

5

(127.0)

3

(76.2)

2

(50.8)

.75

(19.1)

3.47

(88.1)

24

(609.6)

3.13

(79.5)

Front

Plan View

Neutral and

Phase Terminals

#12 to #8 AWG

Vent

Resistors

Grnd Bus

92

(2336.8)

21

(533.4)

Ground Terminals#8 to 500 kcmil

Front View Approx. 650 Lbs. (295 kg)

4 (101.6)

.438 (11.1) Dia. (4)

1.13 (28.7) KOs

(3)

Front View

Control Assembly Approx. 300 Lbs. (136 kg)

17.13

(435.1)

1.13

(28.7)

12.50

(317.5)

(Dimensions May Vary – Shown

Approx. 75 Lbs. (34 kg)

16.38

(416.1)

Front View Side View

28 (203.2)

.375 (9.5) Dia. (4)

5 x 5 (127.0 x 127.0)

Conduit Entry Area

4 (101.6)

1.75

(44.5)

T p V

#8 to 500 kcmil

Neutral andPhase T#12 to #8 AWG

16 (406.4)

17 (431.8)

14(355.6)

13(330.2)

13

(330.2)

13.50

(342.9)

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7.2-6


January 2003


7

Ref. No. 1338

This page intentionally left blank.

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37January 2003

Resistance Grounding SystemNeutral Grounding Resistors


Indoor and Outdoor

277 – 8000 Volts Rated Voltage,480 – 13,800 Volts System Voltage

Grounding Resistor

ApplicationGrounding Resistors are used forseveral purposes in industrial anddistribution systems including:

1. To provide isolation of circuitsunder ground fault conditions.

2. To limit overvoltages on equipmentunder ground fault conditions.

3. To limit ground fault currentand therefore fault damage.

The method of selection is based onOhm’s law E = IR where E is the line-to-neutral voltage, I is the desired maxi-mum ground fault current and R is theohmic value of the grounding resistor.E is obtained by dividing the line-to-line voltage by͙ 3 . I is a value of cur-rent decided upon by the specifyingengineer and is large enough to pro-vide sufficient current for protectiverelaying but small enough to limit faultdamage. R is then the value obtainedfrom the formula E = IR.

Another factor to consider is the timerating. Time ratings of grounding

resistors are as prescribed by IEEEStandard 32-1972 which ranges from10 seconds to continuous. These timeratings refer to the time which theresistor can carry rated currents with-out exceeding its temperature rating.Selection of a time rating is based onallowing enough time for the protec-tive relays to operate or to allow foran orderly shutdown if the systemis monitored instead of relayed.

Table 37.3-1.Rating Times

Temperature ratings are based on760°C rise for resistors rated upthrough one minute, 610°C forextended time and 385°C for continu-ous ratings. Extended time is definedby IEEE as a rating where maximumtemperature rise will not be requiredfor more than an average of 90 daysper year. This extended time ratingalso applies to resistors specified formine duty, as the Federal Registerstates that the rating shall meet the

extended time rating set forth inIEEE Standard 32-1972.

OptionsOptions available include stands,provisions for current transformers,stand-off insulators, entrance bush-ings, and terminal lugs. A resistor withframe covers is used when it is desiredto exclude the possible entry of birds,rodents or other animals from theresistor. The safety enclosure is usedfor personnel safety and completelyencloses the resistor, and live parts.

The resistor stand is another option

which can be used to provide person-nel safety by elevating the resistor outof reach of personnel. A safety enclo-sure can be used in conjunction withthe stand to provide additional safety.

Resistor frames and safety enclosuresare also available with stainless steelor aluminum construction.

FeaturesGrounding resistors will handle allranges of current capacities, timesof operation and ohmic values to suitindividual needs. They are designed,manufactured and tested under strictcontrol and in conformance with IEEE32-1972 standards for neutral ground-ing devices. Standard factory testsinclude overpotential tests for theresistor element, ohmic value, and cir-cuit continuity plus a rigorous inspec-tion of the inner electrical terminalconnections. All grounding resistorsare completely interconnected atthe factory eliminating complicatedwiring installations.

The neutral grounding resistor will beprovided with an outdoor safety enclo-sure. The enclosure will have a solidtop, screened bottom, louvered orscreened side covers, and topmounted eye-bolts for handling ease.The enclosure finish will be mill galva-nized or ANSI 61 gray unless other-wise specified. The enclosure will have8-inch (203.2 mm) legs unless other-

wise specified.

The resistor will consist of stainlesssteel stamped grid edge wound ele-ments, double insulated. The resistorterminals will be stainless steel. Allresistor end frames, hardware andnon-current carrying spacers will bezinc-plated steel. If more than oneresistor frame is required, seriesconnections will be solid copper bus.The resistor bank or banks will bemounted on porcelain standoff insula-tors with a rating equal to or greaterthan the line-to-neutral voltage.

Neutral grounding resistors will be

delivered to the job site completelyassembled and ready for installation.

National Electrical Code and NEC areregistered trademarks of the NationalFire Protection Association, Quincy,Mass. NEMA is the registered trade-mark and service mark of the NationalElectrical Manufacturers Association.UL is a federally registered trademarkof Underwriters Laboratories Inc.

Rating Definition AllowableTemperature

Short Time Normally used with protective relays that will cause thecircuits to be interrupted when fault occurs

760ºC

Extended Time Used where fault currents are permitted for an extended time

period, but cannot average more than 90 days a year

610ºC

Continuous Time Capable of carrying the rated current for an indefiniteperiod of time

385ºC

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7.3-2


January 2003


7

Neutral Grounding Resistors


Table 37.3-2.Ratings — Weights in Lbs. (kg) and Dimensions in Inches (mm)

ᕃ With current transformer included, add 45 lbs. (20 kg) to weight.ᕄ The 347-volt units are tapped for 277-volt use.

VoltsLine-Neutral

CurrentRating

PartNumber

ApproximateWeight ᕃ

AWide

BDeep

CHigh

Ten-Second Ratings

13901390

1390

50100

200

NG13-0-10NG13-1-10

NG13-2-10

300 (136)310 (141)

320 (145)

36 (914.4)36 (914.4)

36 (914.4)

36 (914.4)36 (914.4)

36 (914.4)

24 (609.6)24 (609.6)

24 (609.6)139013901390

300400500

NG13-3-10NG13-4-10NG13-5-10

330 (150)340 (154)350 (159)

36 (914.4)36 (914.4)36 (914.4)

36 (914.4)36 (914.4)36 (914.4)

24 (609.6)24 (609.6)24 (609.6)

139013901390

600800

1000

NG13-6-10NG13-8-10NG13-10-10

360 (163)370 (168)380 (173)

36 (914.4)36 (914.4)36 (914.4)

36 (914.4)36 (914.4)36 (914.4)

24 (609.6)24 (609.6)24 (609.6)

13901390

15002000

NG13-15-10NG13-20-10

390 (177)400 (182)

——

——

——

240024002400

50100200

NG24-0-10NG24-1-10NG24-2-10

450 (204)460 (209)470 (213)

36 (914.4)36 (914.4)36 (914.4)

36 (914.4)36 (914.4)36 (914.4)

32 (812.8)32 (812.8)32 (812.8)

240024002400

300400500

NG24-3-10NG24-4-10NG24-5-10

480 (218)490 (222)500 (227)

36 (914.4)36 (914.4)36 (914.4)

36 (914.4)36 (914.4)36 (914.4)

32 (812.8)32 (812.8)32 (812.8)

24002400

2400

600800

1000

NG24-6-10NG24-8-10

NG24-10-10

510 (232)520 (236)

530 (241)

36 (914.4)36 (914.4)

36 (914.4)

36 (914.4)36 (914.4)

36 (914.4)

32 (812.8)32 (812.8)

32 (812.8)24002400

15002000

NG24-15-10NG24-20-10

540 (245)550 (250)

——

——

——

416041604160

50100200

NG41-0-10NG41-1-10NG41-2-10

600 (272)610 (277)620 (281)

36 (914.4)36 (914.4)36 (914.4)

48 (1219.2)48 (1219.2)48 (1219.2)

36 (914.4)36 (914.4)36 (914.4)

416041604160

300400500

NG41-3-10NG41-4-10NG41-5-10

630 (286)640 (291)650 (295)

36 (914.4)36 (914.4)36 (914.4)

48 (1219.2)48 (1219.2)48 (1219.2)

36 (914.4)36 (914.4)36 (914.4)

416041604160

600800

1000

NG41-6-10NG41-8-10NG41-10-10

660 (300)670 (304)680 (309)

36 (914.4)36 (914.4)36 (914.4)

48 (1219.2)48 (1219.2)48 (1219.2)

36 (914.4)36 (914.4)36 (914.4)

41604160

15002000

NG41-15-10NG41-20-10

690 (313)700 (318)

——

——

——

800080008000

50100200

NG80-0-10NG80-1-10NG80-2-10

800 (363)810 (368)820 (372)

42 (1066.8)42 (1066.8)42 (1066.8)

52 (1320.8)52 (1320.8)52 (1320.8)

60 (1524.0)60 (1524.0)60 (1524.0)

800080008000

300400500

NG80-3-10NG80-4-10NG80-5-10

830 (377)840 (381)850 (386)

42 (1066.8)42 (1066.8)42 (1066.8)

52 (1320.8)52 (1320.8)52 (1320.8)

60 (1524.0)60 (1524.0)60 (1524.0)

800080008000

600800

1000

NG80-6-10NG80-8-10NG80-10-10

860 (390)870 (395)880 (400)

42 (1066.8)42 (1066.8)42 (1066.8)

52 (1320.8)52 (1320.8)52 (1320.8)

60 (1524.0)60 (1524.0)60 (1524.0)

80008000

15002000

NG80-15-10NG80-20-10

890 (404)900 (409)

——

——

——

Extended-Time Ratings

277277

1525

NG277-15NG277-25

65 (30)75 (34)

30 (762.0)30 (762.0)

17 (431.8)17 (431.8)

17 (431.8)17 (431.8)

347ᕄ

347ᕄ1525

NG347-15NG347-25

65 (30)75 (34)

30 (762.0)30 (762.0)

17 (431.8)17 (431.8)

17 (431.8)17 (431.8)

139013901390

152550

NG13-15NG13-25NG13-50

300 (136)350 (159)425 (193)

36 (914.4)36 (914.4)36 (914.4)

36 (914.4)36 (914.4)42 (1066.8)

32 (812.8)32 (812.8)42 (1066.8)

240024002400

152550

NG24-15NG24-25NG24-50

425 (193)550 (250)850 (386)

36 (914.4)36 (914.4)42 (1066.8)

48 (1219.2)48 (1219.2)48 (1219.2)

42 (1066.8)42 (1066.8)60 (1524.0)

416041604160

152550

NG41-15NG41-25NG41-50

850 (386)900 (409)

1300 (590)

42 (1066.8)42 (1066.8)72 (1828.8)

52 (1320.8)52 (1320.8)52 (1320.8)

60 (1524.0)60 (1524.0)60 (1524.0)

Continuous-Time Ratings

277277

510

NG277-5-CNG277-10-C

55 (25)60 (27)

30 (762.0)30 (762.0)

17 (431.8)17 (431.8)

17 (431.8)17 (431.8)

347ᕄ

347ᕄ5

10NG347-5-CNG347-10-C

55 (25)60 (27)

30 (762.0)30 (762.0)

17 (431.8)17 (431.8)

17 (431.8)17 (431.8)

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