Tripping RCD every time it rains
Why it happens here
Moisture gets into outdoor sockets, garden lighting, or damaged cable. St Paul's has plenty of older outdoor wiring that wasn't installed with modern weatherproofing. When water bridges the contacts, the RCD trips to protect you.
Our approach
We use an insulation resistance tester to isolate the affected circuit. Then we inspect outdoor fittings, reseal or replace them, and test again. If the cable itself is damaged, we replace that run with proper outdoor-rated electrical cable.