—Checks and maintenance
Testing an RCD with the test button
The small button marked T on an RCD is there for you to press. It checks the mechanism that protects you from shock.
An RCD switches off when it detects current leaking to earth. Its test button creates a small deliberate imbalance; pressing it should make the RCD switch off immediately. That confirms the switching mechanism moves. Manufacturers recommend testing periodically, and it takes seconds.
Maintenance guides describe the checks that find problems while they are still small.
Pressing the button switches off every circuit the RCD protects, so clocks, timers and some devices may need resetting afterwards. If the RCD does not switch off when the button is pressed, or will not reset afterwards, it needs checking. The button does not measure how quickly the device trips — that requires an instrument test during an inspection.
01In short
The points that matter most
Press and it should trip
Immediately, switching off its circuits.
Reset afterwards
And reset any clocks or timers.
Failure needs attention
A device that does not trip should be checked.
02Detail
What the test shows
Mechanism works
The device can physically switch off.
Not trip speed
Timing is measured with test equipment.
Which circuits it protects
A useful way to learn your board.
Sticking devices
RCDs rarely operated can become stiff; regular testing exercises them.
03Checklist
Before pressing
Warn the household
Lights and sockets will go off.
Save computer work
Desktop computers will lose power.
Know what to reset
Timers, clocks, water heater controls.
04Questions
Questions people ask
- How often should I press the test button?
- Follow the manufacturer’s recommendation printed on or near the device.
- It tripped but will not reset. What now?
- There may be a fault on a circuit; leave it off and have it checked.
- Do RCBOs have test buttons too?
- Yes, each RCBO has its own.
- Is it safe to press?
- Yes. The button is designed for users to operate.
05Related
Related guides
- Maintaining a distribution boardA check that catches the same trouble earlier.
- Outdoor fittings exposed to salt air and sunA check that catches the same trouble earlier.
- Repairing or replacing a distribution boardA related choice for the same kind of work.
- When a socket stops workingAnother thing people notice, with a related check.
This guide sits under maintenance. All topics are on the guides page.
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RCD did not trip when tested?
Tell us which device and what happened. We will arrange a check.