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Littelfuse NGR Series User Manual

Ngr series, Protection relays & controls, Neutral grounding

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Protection Relays & Controls

© 2013 Littelfuse Protection Relays & Controls

Neutral Grounding

NGR SeRieS

Neutral-Grounding-Resistor System

Ordering Information

Littelfuse.com/ngr

SyStem

LiNe-NeutRaL

voLtaGe

NGR

cuRReNt

duty cycLe

dRawiNG

NumbeR

moNitoRiNG compoNeNtS

iN NGR eNcLoSuRe

otheR

optioNS

eNcLoSuRe

StyLe

NGR

X

X

X

– XXXX-RX

X

X

X

X

277, 347,…44000

AMPERES

C = continuous

Assigned

by factory

ER/ = Includes

Sensing Resistor

CT = CT200

N3R = Galvanized

NEMA 3R

10 = 10 seconds

E1 = EFCT-1

30 = 30 seconds

Blank = No

Sensing Resistor

E26 = EFCT-26

ZZ = Zigzag

transformer

(Note: may be

in separate N3R

enclosure)

N3RSS = Stainless

Steel NEMA 3R

60 = 60 seconds

C26 = SE-CS30-26
C70 = SE-CS30-70

Contact factory

for other choices.

Blank = None

OPEN = None

For information about the NGRM-ENC NGR Monitor Control Panel,

see Accessories.

Note: Order SE-325, SE-330, and SE-701 separately.

Rev: 4-A-050213

Description

Neutral-Grounding Resistors (NGRs) are used to ground power

systems by inserting a resistor between the system neutral and

ground. This lowers the prospective ground-fault current to a

predetermined value.
A properly designed resistance-grounded system provides benefits

over both ungrounded and solidly grounded systems. Because the

system is grounded, transient overvoltages do not occur and ground-

fault current can flow, allowing it to be detected and measured. Also,

because a resistor is used to ground the system, the very large and

destructive ground-fault currents of solidly grounded systems are

absent. Ground-fault relays (such as the SE-701) can be used on

feeders to provide selective coordination and the ability to quickly

locate or isolate the fault.

Applications

Resistance grounding is typically applied on transformers and

generators where safety and continuity of service are important. A

faulted feeder may remain in operation until it is safe to repair the fault,

where allowed by the local electrical code.

Benefits

g

Eliminate phase-to-ground arc-flash incidents

g

Eliminate transient overvoltages

g

Reduced point-of-fault damage

g

Can provide continuity of service during a ground fault

Features

g

ER-series Sensing Resistor and Current Transformer required for

NGR monitoring come pre-installed inside the enclosure

g

Can be packaged with a zigzag transformer to resistance ground an

ungrounded delta system, or a system with an inaccessible neutral

g

SE-325 or SE-330 NGR Monitor can provide continuous NGR

monitoring and ground-fault protection; NGR failure will render

current-sensing ground-fault protection inoperative

g

Stainless steel resistor elements prevent corrosion