# Residual current monitor

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

Device with a toroid that measures residual current and gives a warning or signal without interrupting the circuit itself.

## In plain English

### What does Residual current monitor mean?

A residual current monitor measures residual current with a summation toroid around the circuit conductors and signals when it exceeds a threshold. It is used where an unexpected trip would be unacceptable but rising leakage still needs attention, for example in data centres and process plant.

### A simple example

An RCM does not disconnect the circuit by itself, so it is not a substitute for an RCD where automatic disconnection is required. The symbol shows the toroid and monitor, but the reader must find out whether its output drives an alarm only or a separate switching device.

### What the drawings help you do

Check whether the output alarms or trips another device. Confirm that all live conductors, including neutral, pass through the toroid. An RCM signals residual current; an RCD measures it and also disconnects the circuit.

### This particular reference

Device with a toroid that measures residual current and gives a warning or signal without interrupting the circuit itself. An RCM signals residual current; an RCD measures it and also disconnects the circuit.

### Terms

- Terminal: An identified point where a conductor connects.
- Signal: Electrical information passed between devices, rather than necessarily the main power supply.
- 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.

- [Residual current device categories](https://www.se.com/au/en/faqs/FAQ000218859/)
- [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 residual current monitor measures residual current with a summation toroid around the circuit conductors and signals when it exceeds a threshold. It is used where an unexpected trip would be unacceptable but rising leakage still needs attention, for example in data centres and process plant.
An RCM does not disconnect the circuit by itself, so it is not a substitute for an RCD where automatic disconnection is required. The symbol shows the toroid and monitor, but the reader must find out whether its output drives an alarm only or a separate switching device.

## How to read it

- Check whether the output alarms or trips another device.
- Confirm that all live conductors, including neutral, pass through the toroid.

## Information to show or reference

- Show toroid and conductors
- State threshold
- Reference alarm or trip output

## Important distinction

An RCM signals residual current; an RCD measures it and also disconnects the circuit.

## Facts

- Sensing: Summation toroid around live conductors
- Action: Signal or alarm, no integral disconnection
- Preview: Functional illustration of the device role; not a product footprint or certified standard graphic

## Public references

- [Residual current device categories](https://www.se.com/au/en/faqs/FAQ000218859/) — Schneider Electric. Public residual current device categories for comparison with monitoring devices.
- [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 measurement.

## 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.