Why does my RCD trip intermittently with no pattern?

Why Your RCD Keeps Tripping Randomly An RCD (Residual Current Device) is designed to protect you from electric shock and fire by cutting power the instant it detects current leaking to earth. When it trips randomly with no clear pattern, it can feel baffling — but there are logical reasons behind it. What Could Be Causing It? The most common causes of intermittent RCD tripping include: Accumulated earth leakage — Every appliance has a tiny amount of natural leakage current. When many appliances are connected together, their combined leakage can exceed the RCD's 30mA threshold, causing nuisance trips. A faulty appliance — An appliance with deteriorating insulation may only leak current when it warms up, gets wet, or reaches a certain operating condition, making the fault hard to pin down. Moisture ingress — Damp in an outdoor socket, extension lead, or garden appliance can cause leakage that varies with weather conditions. Ageing wiring — Old or damaged cable insulation breaks down over time and leaks more current as it degrades. The RCD itself failing — Older RCDs can develop internal faults and trip at lower thresholds than intended. What You Can Safely Check 1. Unplug everything on the affected circuit and reset the RCD. If it holds, you have an appliance fault. 2. Plug appliances back in one at a time, leaving gaps of a few minutes between each. The trip will return when the faulty item is connected. 3. Check for anything damp — garden tools, outdoor sockets, or appliances used near water. 4. Look at the timing — does it trip overnight, in wet weather, or when the heating comes on? Patterns like these point to moisture or thermal faults. When to Call an Electrician Call a qualified electrician if: The RCD trips even with nothing plugged in You cannot identify the faulty appliance The circuit involves fixed wiring (cookers, showers, immersion heaters) The RCD has tripped more than two or three times without explanation You notice any burning smells, scorch marks, or discoloured sockets Do not tape or wedge the RCD in the on position — this removes a critical layer of protection and is extremely dangerous.