Why your welder trips the breaker
Four separate causes, and they are told apart by when the breaker goes: at switch-on, at the first arc strike, after a few minutes, or only on long runs.
Trips at switch-on: inrush current
An inverter charges a bank of capacitors the instant it is powered up, and for a few milliseconds it draws far more than its rated current. A type B breaker, designed for lighting and sockets, trips at three to five times its rating and sees that as a fault.
The fix is a type C breaker, which tolerates five to ten times the rating briefly. It is a change an electrician makes to the consumer unit; it is not something to work around by using a bigger fuse of the wrong curve.
Trips at the first arc: the machine wants more than the circuit
The welding current is not the input current. A 200 A inverter running at full output on a single phase draws roughly 30 A from the wall — more than a standard 16 A domestic circuit can give.
Work out the real figure with the duty cycle and fuse calculator. If the machine genuinely needs 30 A, the honest answers are a dedicated circuit, a three-phase supply, or welding at lower current with a smaller electrode.
Trips after a few minutes: duty cycle or cable heating
Two possibilities. Either the machine's own thermal protection is cutting in, which is the duty cycle doing its job and not a fault at all — the fan will be running and it will reset in a few minutes. Or the supply cable is undersized, warming up, and the breaker is responding to that.
Tell them apart by feeling the extension lead. A cable that is warm along its whole length is undersized. A drum extension is the classic case: a cable coiled on a drum cannot lose its heat, and its rating drops to roughly a third of the uncoiled figure. Unwind it fully, every time.
Trips the RCD rather than the breaker
Different fault, different cause. An RCD responds to current leaking to earth, not to overload. Damp, a damaged lead, water on the floor or moisture inside the machine will do it — and unlike the others, this one is a genuine safety warning. Do not keep resetting it: find the leakage. The reasoning is in electrical safety in welding.
On a generator
A generator sized to the welder's rated output will still struggle with the inrush. Allow about 30 % margin, prefer an inverter-type generator with a clean waveform, and expect a cheap generator and a cheap inverter together to be an unhappy combination — the welder's power factor correction and the generator's regulation fight each other.
Frequently asked questions
Type B or type C breaker?
Type C. An inverter draws a large inrush current when it switches on, charging its internal capacitors, and a type B curve trips on exactly that. Type C tolerates the inrush and still protects the cable. This is a job for an electrician, not a heavier fuse.
Can I just fit a bigger breaker?
Not without checking the cable. The breaker protects the wiring, not the welder: fitting a 25 A device on a circuit wired for 16 A removes the protection and leaves the cable to overheat inside a wall. If the machine genuinely needs more, the circuit needs upgrading.
It only trips after ten minutes of welding.
Then it is thermal, not inrush, and the machine is probably being run above its duty cycle — or the supply cable is undersized and warming up. Work out the real input current and duty cycle with the duty cycle calculator.
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