# Neutral earthing resistor

Canonical URL: https://eloragrid.ai/symbols/neutral-earthing-resistor
Publisher: Elora Grid
Updated: 2026-10-28
Lookup label: NER
Drawing use: SLD, Schematic
Reference families: IEC, IEEE / ANSI

A resistor between a transformer or generator neutral and earth that limits earth-fault current to a set value.

## In plain English

### What does Neutral earthing resistor mean?

A neutral earthing resistor connects the star point of a transformer or generator to earth through a defined resistance. It limits earth-fault current, typically to tens or hundreds of amperes on medium-voltage systems and a few amperes on high-resistance earthed low-voltage systems, reducing damage and arc energy while keeping enough current for protection to detect.

### A simple example

Drawings show a resistor between the neutral of a star winding and the earth symbol, often with a current transformer in the neutral lead for earth-fault protection and sometimes a disconnector. The resistor current and time rating, such as 400 A for 10 seconds, are written beside it.

### What the drawings help you do

The symbol does not show the resistor's monitoring, which some designs use to detect an open resistor. It also does not show whether generator and transformer neutrals are earthed at the same time, which affects fault current and circulating harmonic currents.

### This particular reference

A resistor between a transformer or generator neutral and earth that limits earth-fault current to a set value. A neutral earthing resistor limits fault current resistively; an arc suppression coil compensates capacitive fault current with inductance.

### Terms

- Winding: A coil of conductor inside an electrical machine or transformer.
- Terminal: An identified point where a conductor connects.
- Rating: A value stating the conditions for which equipment is specified.

Concept diagram: Identify the device and form → Read the connections and state → Check the equipment reference
A guide to reading this reference. The original symbol illustration and its drawing notes appear below; these boxes are not a wiring diagram.

- [Neutral grounding resistor and transformer resources](https://www.postglover.com/literature-library/)
- [Residual current and neutral-earthing protection context](https://new.abb.com/medium-voltage/digital-substations/campaigns/earth-fault-protection-portfolio/earth-fault-offering)


## What it represents

A neutral earthing resistor connects the star point of a transformer or generator to earth through a defined resistance. It limits earth-fault current, typically to tens or hundreds of amperes on medium-voltage systems and a few amperes on high-resistance earthed low-voltage systems, reducing damage and arc energy while keeping enough current for protection to detect.
Drawings show a resistor between the neutral of a star winding and the earth symbol, often with a current transformer in the neutral lead for earth-fault protection and sometimes a disconnector. The resistor current and time rating, such as 400 A for 10 seconds, are written beside it.
The symbol does not show the resistor's monitoring, which some designs use to detect an open resistor. It also does not show whether generator and transformer neutrals are earthed at the same time, which affects fault current and circulating harmonic currents.

## How to read it

- Read the current and time rating together.
- A neutral CT normally feeds earth-fault protection.

## Information to show or reference

- State resistance, current and time rating.
- Show neutral CT and disconnector.
- Reference earth-fault protection settings.

## Important distinction

A neutral earthing resistor limits fault current resistively; an arc suppression coil compensates capacitive fault current with inductance.

## Facts

- Connection: Neutral to earth
- Rating: Current and time, for example 400 A 10 s
- Associated protection: Neutral CT earth-fault relay
- Preview: Independent educational illustration; consult the applicable standard and project legend for the exact graphic

## Public references

- [Neutral grounding resistor and transformer resources](https://www.postglover.com/literature-library/) — Post Glover. Public neutral earthing resistor resource library.
- [Residual current and neutral-earthing protection context](https://new.abb.com/medium-voltage/digital-substations/campaigns/earth-fault-protection-portfolio/earth-fault-offering) — ABB. Public neutral earthing and earth-fault protection context.

## Graphic scope

Independent original educational concept illustration by Elora Grid. Not a certified standards graphic or manufacturer footprint. Unitless; not to scale. Original artwork licence: https://creativecommons.org/licenses/by/4.0/. Publisher material is linked only.