# Earth-fault current relay

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

Measuring relay form that operates on current flowing to earth, fed from a residual connection or core-balance CT.

## In plain English

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

The earth-fault current relay form identifies a relay whose operating quantity is current flowing to earth. It may be fed from a core-balance CT around all live conductors, from the residual connection of three phase CTs, or from a CT in the star-point earth lead, and the source changes its achievable sensitivity.

### A simple example

The relay box shows the quantity with an earth additional drawing mark but not the setting, characteristic or whether it is directional. In resistance-earthed and isolated networks earth-fault current is small and often needs a sensitive or directional element that must be stated separately.

### What the drawings help you do

Identify the CT arrangement that supplies the residual current. Check whether the element is directional or sensitive. An earth-fault current relay measures current to earth; an earth-fault voltage relay measures neutral displacement voltage.

### This particular reference

Measuring relay form that operates on current flowing to earth, fed from a residual connection or core-balance CT. An earth-fault current relay measures current to earth; an earth-fault voltage relay measures neutral displacement voltage.

### Terms

- Coil: A wound conductor that can produce a magnetic field when energised.
- Phase: One of the related AC waveforms in a power system.
- Terminal: An identified point where a conductor connects.

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: Current monitoring relays](https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-E0DDA638-4664-4F1E-B191-29A4C40C4A0A.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

The earth-fault current relay form identifies a relay whose operating quantity is current flowing to earth. It may be fed from a core-balance CT around all live conductors, from the residual connection of three phase CTs, or from a CT in the star-point earth lead, and the source changes its achievable sensitivity.
The relay box shows the quantity with an earth qualifier but not the setting, characteristic or whether it is directional. In resistance-earthed and isolated networks earth-fault current is small and often needs a sensitive or directional element that must be stated separately.

## How to read it

- Identify the CT arrangement that supplies the residual current.
- Check whether the element is directional or sensitive.

## Information to show or reference

- Show residual CT source
- State setting and characteristic
- Reference system earthing method

## Important distinction

An earth-fault current relay measures current to earth; an earth-fault voltage relay measures neutral displacement voltage.

## Facts

- Measured quantity: Residual or earth-fault current
- Publisher reference token: HCR1F37 (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: Current monitoring relays](https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-E0DDA638-4664-4F1E-B191-29A4C40C4A0A.htm) — Autodesk. Public AutoCAD Electrical relay listing that names the Ground Failure Current 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 residual current and neutral-earthing 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.