How would you diagnose a tripping RCD in a bathroom circuit without replacing components?

• A. Replace the RCD with a new one immediately
• B. Rely on manual dampness tests
• C. Isolate loads, use RCD test to rule out a fault; check for leakage or equipment faults and if necessary test with a substitute device
• D. Disable the circuit and ignore tripping

Answer: (C)

Diagnosing a tripping RCD without swapping parts is about a safe, methodical check of the circuit to locate the fault. Start by isolating the bathroom circuit from the supply so nothing is energized. Use the RCD’s built‑in test button to confirm the device will trip under a deliberate imbalance, which shows the RCD itself is capable of operating. Then re-energize with loads isolated and either reconnect them one by one or test with a known-good substitute device to see if a particular appliance or a section of the circuit is causing leakage to earth. Inspect for moisture, damaged insulation, or faulty equipment, especially in a bathroom. If the substitute device still trips or you can’t locate the fault, further steps may be needed, but the goal is to identify the fault without unnecessary replacement. Never disable the circuit and ignore the tripping.