Fault finding and trade tips

Why does an RCD keep tripping, and how do you find the fault?

An RCD that keeps tripping is usually down to one of four things: a faulty appliance, an insulation fault (often damp or damaged cable), a neutral-to-earth fault, or too much normal earth leakage adding up across the circuits it protects. Occasionally the RCD itself is over-sensitive. Find it methodically: unplug everything, split the circuits, then isolate properly and insulation-test circuit by circuit, remembering that switching off an MCB doesn't disconnect the neutral.