I don't really want to sidetrack this thread but ...
Back in the early '70s, I was a draughtsman at Martin Electric, Theale, where we made spot welders. Our 'small' ones used a 25kVA transformer, which delivered a mere 500,000 Amps - the secondary-cables were about 1.5 inches diameter. All parts of the secondary circuit i.e. transformer, cables and welding-head, were water cooled, they reckoned the current 'leaked' through the water was negligible compared to what went through the weld.
The transformers had 3-phase primary windings and a secondary comprising two turns. Each of those turns was cast copper, up to an inch by four cross section, with a coolant-pipe cast-in, in the form of a U-shape and connected in series. The secondary voltage was probably only a Volt or two, it was Amps we wanted!
The controllers comprised a timer switching thyratrons - the valve-type precursor to the thyristor (thyratron transistor ) - on all three phases of the mains power.
Since then, my interest in electronics has used FAR smaller currents but has gradually dwindled. I built my first CNC machine to overcome my failing eyesight so as to drill the holes in my PCBs.
And that in turn has led )eventually) to my current build of a CNC milling-machine.
Which is calling me just now to do some more work.
Geoff
Thailand