# Arc suppression coil

Canonical URL: https://eloragrid.ai/symbols/arc-suppression-coil
Publisher: Elora Grid
Updated: 2026-10-28
Lookup label: ASC
Drawing use: SLD
Reference families: IEC, IEEE / ANSI

An adjustable reactor between neutral and earth tuned to cancel the network capacitive earth-fault current.

## In plain English

### What does Arc suppression coil mean?

An arc suppression coil is a reactor connected between the system neutral and earth, tuned so that its inductive current balances the capacitive current that flows during a single phase-to-earth fault. The residual fault current becomes very small, so transient arcing faults often self-extinguish and the network can keep running with a sustained earth fault.

### A simple example

Drawings show an inductor with an adjustment arrow between a transformer or earthing transformer neutral and earth, often with a parallel resistor switched in briefly to help fault location. Automatic tuning controllers and neutral voltage measurement are drawn alongside.

### What the drawings help you do

Resonant earthing needs dedicated earth-fault detection, such as transient or admittance-based protection, because fault current is too small for simple overcurrent relays. The symbol does not show the tuning range or the detection method.

### This particular reference

An adjustable reactor between neutral and earth tuned to cancel the network capacitive earth-fault current. An arc suppression coil cancels capacitive fault current; a neutral earthing resistor limits fault current but does not cancel it.

### Terms

- Winding: A coil of conductor inside an electrical machine or transformer.
- Coil: A wound conductor that can produce a magnetic field when energised.
- Phase: One of the related AC waveforms in a power system.

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.

- [Residual current and neutral-earthing protection context](https://new.abb.com/medium-voltage/digital-substations/campaigns/earth-fault-protection-portfolio/earth-fault-offering)
- [AutoCAD Electrical: Reactors and inductors](https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-BAD50DBF-0951-44A0-BB4C-A57B4A4ED895.htm)


## What it represents

An arc suppression coil is a reactor connected between the system neutral and earth, tuned so that its inductive current balances the capacitive current that flows during a single phase-to-earth fault. The residual fault current becomes very small, so transient arcing faults often self-extinguish and the network can keep running with a sustained earth fault.
Drawings show an inductor with an adjustment arrow between a transformer or earthing transformer neutral and earth, often with a parallel resistor switched in briefly to help fault location. Automatic tuning controllers and neutral voltage measurement are drawn alongside.
Resonant earthing needs dedicated earth-fault detection, such as transient or admittance-based protection, because fault current is too small for simple overcurrent relays. The symbol does not show the tuning range or the detection method.

## How to read it

- An adjustment arrow on the reactor shows tuning capability.
- Look for a parallel resistor used for fault location.

## Information to show or reference

- State tuning range in amperes.
- Show earthing transformer and resistor.
- Reference earth-fault detection method.

## Important distinction

An arc suppression coil cancels capacitive fault current; a neutral earthing resistor limits fault current but does not cancel it.

## Facts

- Element: Adjustable reactor
- Connection: Neutral to earth
- Detection required: Sensitive or transient earth-fault protection
- Preview: Independent educational illustration; consult the applicable standard and project legend for the exact graphic

## Public references

- [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 earth-fault and neutral earthing protection context.
- [AutoCAD Electrical: Reactors and inductors](https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-BAD50DBF-0951-44A0-BB4C-A57B4A4ED895.htm) — Autodesk. Public reactor symbol family 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.