# Earth-fault voltage relay

Canonical URL: https://eloragrid.ai/symbols/earth-fault-voltage-relay
Publisher: Elora Grid
Updated: 2026-10-28
Lookup label: K
Drawing use: Schematic, SLD
Reference families: IEC, Manufacturer

Relay form that operates on a voltage appearing because of an earth fault, such as between a frame and earth.

## In plain English

### What does Earth-fault voltage relay mean?

This relay measures a voltage that appears only when there is an earth fault, for example between exposed metalwork and a reference earth, or across a neutral earthing impedance. It is useful where earth-fault current is limited and a voltage is easier to detect than a current.

### A simple example

The symbol does not say where the voltage is measured. A relay across a neutral earthing resistor and one connected between frame and auxiliary earth electrode have very different settings, so the measurement points must be drawn and labelled.

### What the drawings help you do

Trace both measurement connections of the relay. Check the reference earth used by the relay. An earth-fault voltage relay measures fault-related voltage; a residual voltage relay measures zero-sequence voltage from VT windings.

### This particular reference

Relay form that operates on a voltage appearing because of an earth fault, such as between a frame and earth. An earth-fault voltage relay measures fault-related voltage; a residual voltage relay measures zero-sequence voltage from VT windings.

### Terms

- Coil: A wound conductor that can produce a magnetic field when energised.
- Rating: A value stating the conditions for which equipment is specified.
- Schematic: A drawing showing function and connections rather than physical appearance.

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.

- [AutoCAD Electrical: Voltage monitoring relays](https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-5296749E-9336-4B07-9956-160963D6C848.htm)
- [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

This relay measures a voltage that appears only when there is an earth fault, for example between exposed metalwork and a reference earth, or across a neutral earthing impedance. It is useful where earth-fault current is limited and a voltage is easier to detect than a current.
The symbol does not say where the voltage is measured. A relay across a neutral earthing resistor and one connected between frame and auxiliary earth electrode have very different settings, so the measurement points must be drawn and labelled.

## How to read it

- Trace both measurement connections of the relay.
- Check the reference earth used by the relay.

## Information to show or reference

- Show measurement points
- State threshold and delay
- Reference earthing arrangement

## Important distinction

An earth-fault voltage relay measures fault-related voltage; a residual voltage relay measures zero-sequence voltage from VT windings.

## Facts

- Measured quantity: Voltage caused by an earth fault
- Publisher reference token: HCR1F31 (Autodesk identifier; not an IEC database ID)
- Preview: Independent educational concept; consult the publisher and applicable standard for the exact graphic

## Public references

- [AutoCAD Electrical: Voltage monitoring relays](https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-5296749E-9336-4B07-9956-160963D6C848.htm) — Autodesk. Public AutoCAD Electrical relay listing that names the Ground Failure Voltage Protection block; the illustration is independently drawn.
- [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 context for neutral-earthing and earth-fault protection.

## 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.