Why Does My RCD Keep Tripping? 9 Causes & How to Find the Fault An RCD that keeps tripping is doing exactly what it's designed to do — it has almost certainly detected a real imbalance between line and neutral current, not developed a fault of its own. In most cases the cause is a leaking appliance, damp cabling outdoors, or several small "healthy" leakages from filtered equipment adding up on one shared RCD, rather than the device itself being defective. Replacing a tripping RCD without finding out why it tripped usually just moves the same nuisance trip onto the next one. This guide covers the nine most common reasons an RCD keeps tripping, how to narrow down which circuit or appliance is responsible, and when the RCD genuinely is the faulty part — for maintenance electricians on a call-out and facilities engineers trying to stop a nuisance trip from taking out a whole distribution board. Don't just keep resetting it. An RCD that trips repeatedly is reporting a real leakage path to earth. Repeated resetting without investigating risks re-energizing a genuine fault — such as damaged cable insulation or a failing appliance — that could become a shock or fire risk. All checks below assume safe isolation by a competent person before any wiring is touched. Talk to Our Expert Team How an RCD Actually Detects a Fault An RCD works by comparing the current flowing out to a circuit on the line conductor against the current returning on the neutral conductor. Both pass through a toroidal current transformer inside the device; in a healthy circuit, the two currents are equal and their magnetic fields cancel out. The moment some current finds a path to earth instead of returning through neutral — through a person, damp insulation, or a faulty appliance casing — that balance is broken. The transformer detects the resulting differential current, and once it crosses the rated tripping threshold (commonly 30 mA for personal protection), a trip relay fires and opens the contacts within milliseconds. Nothing about this process cares whether the leakage is dangerous or completely benign — it trips on the imbalance itself, which is exactly why nuisance tripping from harmless sources is so common. Line and neutral conductors pass through a toroidal sensing coil. When current leaks to earth instead of returning on neutral, the coil detects the imbalance and fires a trip relay that opens the contacts. Supply Line Neutral Toroidal sensing coil Contacts Load / appliance Leakage to earth (imbalance) Trip relay fires when imbalance > rated mA RCD Types at a Glance Type Detects Type AC Sinusoidal AC residual current only — the most basic and increasingly unsuitable for modern loads Type A AC plus pulsating DC residual current — required for most modern electronic loads Type B AC, pulsating DC, and smooth DC residual current — needed for three-phase drives, PV inverters and EV charging RCBO Combines RCD earth-fault protection with MCB overcurrent protection in one device, per final circuit 9 Causes of an RCD Tripping Repeatedly 1 A Genuinely Faulty Appliance By far the most common cause. Kettles, washing machines, immersion heaters, and outdoor power tools are frequent offenders because their heating elements or motors sit close to earthed metal casework, and insulation breakdown there leaks current straight to earth. Unplug everything on the affected circuit, reset the RCD, then reconnect appliances one at a time — the one that trips it again is the culprit. 2 Damp or Water Ingress in Cabling and Enclosures Outdoor sockets, garden lighting, and cable joints in unsealed enclosures are classic sources of moisture-related leakage — and the trip often correlates neatly with rain or humidity. Water doesn't need to be visible; a compromised gland or a cracked junction box can let in enough moisture to bridge a leakage path long before anything looks obviously wet. Isolate outdoor circuits first when tripping tracks with weather. 3 A Shared or Borrowed Neutral If a neutral conductor from one circuit has been cross-connected onto another — common in older installations that have been added to over the years — some of that circuit's return current takes a path outside the RCD's sensing coil entirely. The device reads this as an imbalance and trips even though there's no earth fault at all. This is a wiring fault, not a device fault, and it needs tracing at the distribution board and downstream junctions. 4 Cumulative Leakage From Multiple Filtered Loads Modern electronics — PCs, VFDs, LED drivers, switch-mode power supplies — all contain small EMC filter capacitors between line/neutral and earth that leak a tiny, permitted amount of current by design. One or two on a circuit is harmless, but a distribution board with dozens of them sharing a single 30 mA RCD can add up to a trip with no single "faulty" item at all. This shows up as a trip that happens only once a certain number of devices are switched on together, and the long-term fix is sp…