What is this?
When your RCD trips during or after rain, moisture is almost certainly getting into your electrical installation somewhere. Water is conductive and creates an earth leakage path that the RCD detects. This is a serious issue because the combination of water and electricity creates a significant risk of electric shock.
Common causes
- Water ingress into an outdoor socket, light, or junction box with failed seals
- Damaged or deteriorated cable insulation on external wiring
- Leaking roof allowing water to drip onto light fittings or wiring in the loft
- Faulty damp-proof course allowing moisture into sockets on external walls
- Condensation in an outbuilding, shed, or garage with poor ventilation
- Underground cable to a garden building with damaged sheathing
Is it dangerous?
This is a high-risk situation. Water and electricity are a dangerous combination, and the fault will likely worsen with each episode of rain. The RCD is protecting you from a potentially lethal shock, but the underlying water ingress needs to be found and fixed urgently. There is also a risk of corrosion damage to wiring and fittings that could cause a fire.
Can I fix it myself?
Do a visual inspection of all outdoor electrical fittings including garden lights, external sockets, outbuilding supplies, and security lights. Look for obvious signs of water entry, cracked covers, or missing seals. Check the loft for water near any cables or light fittings. Do not open or touch any fitting that appears wet — isolate the circuit first.
When to call an electrician
Call an electrician as soon as possible. Rain-related tripping indicates water in the electrical installation, which is a serious safety issue. The problem will not fix itself and will get worse over time as water causes further corrosion and insulation breakdown. An electrician needs to find and seal the point of water ingress.
What will an electrician do?
Systematically isolate circuits to identify which one is affected by moisture
Inspect all outdoor and exposed fittings for signs of water ingress
Carry out insulation resistance testing in both dry and wet conditions to pinpoint the fault
Replace damaged fittings with appropriate IP-rated enclosures for outdoor use
Repair or reroute damaged cables and restore weatherproof seals
Recommend improvements such as IP65-rated outdoor sockets and proper cable entry grommets
Typical cost
£120 – £300
Costs depend on the location and extent of water ingress. Replacing outdoor fittings and re-sealing is at the lower end. Rerouting cables or repairing underground feeds costs more.
