Littelfuse NGR Series - Manual

Protection Relays & Controls
© 2013 Littelfuse Protection Relays & Controls
Neutral Grounding
NGR SeRieS
Neutral-Grounding-Resistor System
Ordering Information
Littelfuse.com/ngr
SyStem
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NGR
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duty cycLe
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NumbeR
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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