Duty cycle and fuse size
How long the machine can weld before the thermal cut-out stops it, and what the supply behind it has to be able to deliver.
Reading the plate
Duty cycle is quoted over a ten-minute cycle, as EN 60974-1 defines it. "160 A at 60 %" means six minutes of welding and four of cooling — with the fan running, which is why switching the machine off at the end of a run is exactly the wrong thing to do.
Duty cycle rises steeply as current falls: it goes with the square of the current ratio. The same machine that manages 60 % at 160 A will run continuously at about 125 A.
The supply side
The input current is not the welding current. It follows from the arc power divided by the mains voltage and the efficiency, which is why a 200 A inverter on a single phase can draw 30 A from the wall. Two practical consequences: use a type C breaker, because the inrush of an inverter trips a type B, and size a generator with a margin of about 30 %.
If the breaker trips anyway, the reasons are laid out in why your welder trips the breaker.
The breaker curve
| Curve | Trips at | Suits welding |
|---|---|---|
| B | 3–5 × rated current | No — it trips on the inrush surge |
| C | 5–10 × rated current | Yes — the usual choice for a workshop |
| D | 10–20 × rated current | For heavy machines — specified by the electrical design |
Frequently asked questions
Why will a 16 A breaker not hold?
Because the mains current is not the welding current. 160 A of welding at 230 V draws 25 to 30 A on the supply side, depending on efficiency. On top of that comes the inrush at switch-on, which a type B breaker reads as a fault.
What does 60 % duty cycle mean?
Six minutes of welding and four of cooling in every ten-minute cycle to EN 60974-1, at the stated current. At a lower current the welding time grows — which is exactly what this calculator works out.
Which generator is big enough?
Take the apparent power of the machine and add about 30 % for the inrush. A generator that fits on paper sags when the arc strikes, and repeated undervoltage damages an inverter more than overload does.
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