Fault Finding and Repair in IP33

Fault finding is time on the tools, not a part. Tracing a tripping RCD takes twenty minutes or half a day, and nobody can price that over the phone without seeing the installation. The repair itself is usually the cheap end of the job.

The method is dull and it works. Unplug everything first, because a faulty appliance trips an RCD far more often than faulty wiring does. Immersion heaters, washing machines, freezers and anything used outdoors lead that list. Circuits then go back on one at a time until the fault reappears. That circuit gets half-split and tested from the middle, over and over, until the fault sits between two known points. Insulation resistance is tested at 500 V DC between line, neutral and earth.

Which device operated is the first clue. An MCB trips on overload or a short circuit. An RCD trips on earth leakage above roughly 30 mA. Different problems, different search.

Repairs to an existing circuit are certified on a Minor Electrical Installation Works Certificate. A new circuit or a board change needs an Electrical Installation Certificate.