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.

The current the duty cycle is quoted at
For example 60 % at 160 A
Inverter 85–90, transformer 65–75

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.

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