Littelfuse.com

© 2020 Littelfuse, Inc.

Rev: 1-B-031920

1 of 9

Protection Relays & Controls

NGR SERIES – US

Description

High-resistance grounding prevents many of the problems

that are associated with ungrounded and solidly grounded

electrical distribution and utilization systems. High-resistance

grounding can limit point-of-fault damage, eliminate transient

overvoltages, reduce the arc-flash hazards, limit voltage

exposure to personnel, and provide adequate tripping levels

for selective current-based ground-fault detection and

coordination.

The Littelfuse Neutral Grounding Resistor System is a

neutral grounding resistor (NGR), current transformer, and

sensing resistor installed in a NEMA 3R enclosure used to

high-resistance ground transformers and generators. The

NGR system is designed for use with Littelfuse Neutral

Grounding Resistor Monitors for complete system grounding

and grounding protection.

The NGR series – US systems are designed for use in US

applications and all other parts of the world, not including

Canada. For applications in Canada, please use the NGR

series – Canada.

Applications

High-resistance grounding is 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.

Features

Enclosure

The NGR Series – US comes pre-installed in a

ventilated NEMA 3R galvanized steel enclosure

and components are pre-wired to terminals for

ease of installation. Back view shown on left.

ER Series Sensing Resistor

Use with the SE-325 or the SE-330 to continuously monitor

the continuity of a neutral-grounding resistor and eliminate

hazardous voltage levels at the relay.





ER-600VC is designed for use on systems up

to 600 V for indoor applications. Available in

optional moisture-proof enclosure (shown on

left) for outdoor applications.





ER-5KV for use on systems up to 4160 V for

indoor applications.





ER-5WP is designed for use on systems up

to 4160 V and comes with weather-protected

terminals for outdoor installations.

Earth-Fault Current Transformer

Used with the SE-325 or the SE-330 to measure ac current

flowing through the NGR for use with the continuity

monitoring circuit and to detect ground faults.





ELCT5-31 used with SE-330 for 5 A

and 10 A NGRs.





SE-CS10-2.5 used with SE-330 for 10 A

and 15 A NGRs.





CT200 used with the SE-325 for all

applications.





5SHT-101-E (not shown) used with SE-330 for

25 A NGRs.

Benefits





Eliminate phase-to-ground arc-flash incidents





Eliminate transient overvoltages





Reduce point-of-fault damage





Can provide continuity of service during a ground fault





Includes current transformer and ER series sensing

resistor for use with Littelfuse monitoring relay and for

ease of installation.

Neutral Grounding Resistor System

OR