Why does my drill trip the RCD or the breaker?
Telling an overload trip from an earth-leakage trip, the three usual causes on a power tool, and where the diagnosis stops being a DIY job.
- Difficulty
- beginner
- Time
- 15 min
- Read
- 4 min
- Safety
- warning
Short answer
If the breaker trips when the drill labours, it is an overload or inrush issue. If the RCD trips — often taking other circuits with it — it is earth leakage, usually from a damaged lead, a wet tool or motor damage. Test the tool on a different circuit and test the circuit with a different tool; that pair of tests locates it.
Two different devices trip for two different reasons and people describe both as the trip going. A breaker responds to too much current. An RCD responds to current leaking to earth, which is what happens through a person. Knowing which one operated tells you most of what you need, and the front of the consumer unit shows it.
Safety
Step by step
- Identify which device operated.Look at the consumer unit. A single small breaker off is an overcurrent trip on that circuit. A larger RCD or RCBO off, particularly if several circuits are dead, is an earth-leakage trip.
- Do the two swap tests.Same tool, different circuit: if it still trips, the tool is the problem. Different tool, same circuit: if that trips too, the circuit or the installation is the problem.
- Inspect the lead and plug closely.Flex it end to end, look at both strain reliefs, check for tape or crushing, and look inside the plug if it is a rewireable one for loose strands and a correct fuse.
- Dry everything before retrying.Tools and leads used outdoors or in a damp garage collect moisture, and moisture is the single most common cause of nuisance RCD trips with power tools.
- Stop where DIY stops.If it is not the tool and not moisture, the investigation is inside the fixed installation. That is an electrician's work, and continuing to reset a tripping RCD is not an option.
Tips
- Always use an RCD for outdoor and garage work, either at the socket, in a plug-in adaptor or in the consumer unit. A drill through a cable outdoors, in the wet, is exactly the scenario RCDs exist for.
- Cable reels used coiled overheat under load and can also cause nuisance tripping. Unwind them fully.
- If a tool trips an RCD once and never again after drying out, note it and watch it. If it happens a second time, retire the tool.
If it doesn't work
Trips the instant the trigger is pulled, every time
Cause: A short or heavy earth leakage in the tool or its lead — Fix: Take the tool out of use. Test it on a different circuit to confirm it follows the tool, then have the lead and tool checked or replace it.
Trips only when the drill is working hard
Cause: Overload, or a marginal circuit with other loads on it — Fix: Check what else is on the circuit, work in shorter bursts, and use a tool matched to the job. A drill stalling repeatedly draws heavy current each time.
RCD trips and takes several circuits with it
Cause: Cumulative earth leakage across the installation with the tool as the last straw — Fix: Unplug everything else on the affected circuits, then reintroduce loads one at a time. Older appliances leak small amounts, and the total can sit just below the threshold until a tool is added.
Trips outdoors or in the wet, not indoors
Cause: Moisture in the tool, the lead or the connection — Fix: Stop, dry everything thoroughly and use outdoor-rated leads and connectors. Water in an extension coupling is a very common cause and a genuine shock risk.
Trips when the lead is moved or flexed
Cause: Damaged cable, most often at the plug or at the tool's strain relief — Fix: Take it out of use. An intermittent fault in a flexing lead is exactly the fault that becomes a shock.
Old corded tool trips a new RCD but never used to
Cause: A motor with accumulated moisture or degraded insulation, now detected by more sensitive protection — Fix: Sometimes drying the tool out in a warm room for a day cures it. If it recurs, the insulation is failing and the tool is finished.
Trips at switch-on but runs fine afterwards
Cause: Inrush current from a large motor on a marginal breaker — Fix: Use a different circuit, or a socket closer to the consumer unit. Nothing is necessarily faulty, but repeated tripping is worth an electrician's opinion.
Questions people ask
Can I use a drill on a circuit without an RCD?
Not sensibly, and outdoors or in a damp location it is genuinely dangerous. A plug-in RCD adaptor costs very little and is the answer if the circuit does not have one.
Why does my new RCD trip on a tool that was fine for years?
Modern devices are more sensitive and modern installations put more circuits behind them. The tool has probably been leaking slightly for years and nothing was detecting it.
Is a tripping breaker damaging my drill?
The trip itself is not. What causes it — repeated stalling, an overloaded motor or a fault — may well be, and that is the thing to address.