How is an RCD trip test performed, and what indicates correct operation?

• A. Replace the fuse in the device; the device should continue to operate.
• B. Press the test button or apply a test current; the device should trip within its specified time, cutting the supply.
• C. Switch off the main breaker for 5 minutes; the device should reset.
• D. Measure voltage with a multimeter; observe no change.

Answer: (B)

Testing an RCD focuses on its ability to sense an imbalance between live and neutral and trip quickly to cut the supply. The standard method is to press the built-in test button (or inject a small test current) which briefly creates a leakage-like imbalance. If the RCD is functioning, it should trip and disconnect the protected circuit within its specified time.

What indicates correct operation is that the circuit is suddenly de-energized when the test is performed—the device trips, its indicator shows, and the supply to the protected outlets or circuit is cut. After tripping, reset it by switching the circuit off and then back on or using the reset button, depending on the model.

The other options don’t verify this behavior: replacing a fuse and continuing to operate does not test the RCD and is unsafe; switching off the main breaker for a short period doesn’t test the RCD’s ability to sense leakage; measuring voltage with a multimeter and seeing no change doesn’t confirm the RCD will trip under fault conditions.