Mike,
Of all the things I took note of, the brand was not one of them. I will find out tonight. It was a name-brand welder and not some home-made lash-up.
Commercial welder in a domestic workshop, yes. Rated at 60% duty cycle at full output current. My friend welded up a box from pieces of 6mm plate. Not a completely continuous run, but 8 x ~150mm welds in quick succession. He is going to be adding extra steel beams into a large trailer of the sort usually pulled by a big-rig type truck, and he was quite adamant that the test weld was fairly typical of what would be needed on this job.
The socket outlet in question was a 15A, in keeping with the 15A plug on the welder.
The MCB is built in to the cabinet of the welder, and serves as a main switch. Presumably it also offers some protection to the welder if it suffers a fault internally.
I wonder if the distortion of the mains waveform by the switchmode inverter is causing my clamp meter to give a reading higher than the true value. The fact remains, though, that the welder does draw more current when welding than the rating of the plug and cord, and only gets a rest between welds. Safe? Probably, given good upstream protection. Legal? I have doubts.
