Two electricians had been out and basically shrugged. Mike was here for forty minutes with a proper tester and found a damaged cable in the dining room ceiling we'd had no idea about. Repaired it the same morning. He didn't just reset the trip and run, which is what the others did. That's the difference.
The Boughton circuit that tripped at 3am
Mark's upstairs ring kept tripping the RCD overnight, never during the day. Took us forty minutes to find why.
Mark rang on a Tuesday. His upstairs ring main had tripped the RCD three nights running, always between 2am and 4am, never during the day. He'd already had two electricians out who'd reset it, said it was 'probably the immersion heater', and left.
We turned up Wednesday morning with a Megger and a hunch. Forty minutes of insulation resistance testing on each branch of the ring narrowed it down to a downstairs spur — a nail had been driven through 6242Y cable in the dining room ceiling, sometime in the past, just barely missing the live conductor. Damp from the bathroom above was getting into the cable overnight, the resistance was dropping below 30mA, and the RCD was doing exactly what it was meant to.
Replaced the damaged section, tested the whole ring again, told Mark to put a new extractor fan in the bathroom because the underlying problem was condensation. He's not had a trip since.
The reason the previous electricians missed it: they reset the trip and stopped. They didn't test.
Materials & specifications
- Test equipment
- Megger MFT1741 (insulation resistance, RCD test)
- Replacement
- 1.5m of 2.5mm 6242Y cable, BS EN 60670 junction box