CBCT
Core-balance current transformer
A core-balance CT measures residual current from the net magnetic effect of conductors passing through its window.
SLD / Schematic
Symbols · RCM
Residual current monitor
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.
- 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.
Read the source: Residual current device categories · Residual current and neutral-earthing protection context
SLD / Schematic · RCM
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
A distinction that matters
An RCM signals residual current; an RCD measures it and also disconnects the circuit.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
Residual current device categories
Public residual current device categories for comparison with monitoring devices.
Residual current and neutral-earthing protection context
Public context for residual current measurement.
About this graphic
This illustration was authored independently by Elora Grid to explain the concept. It is not reproduced from a customer drawing, an official standard graphic or a manufacturer CAD file. Its correspondence to an exact IEC or IEEE symbol identifier has not been certified.
SVG and DXF downloads contain this original artwork. DXF uses unscaled drawing units; a GA envelope supplies no product dimensions, clearances or fabrication information. Original artwork is available under CC BY 4.0. Third-party references retain their own terms.
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