So my mate had a gate he wanted welded up, located about 100m (by his estimate) from the nearest power point. He has a genny, but only 2kW and 100m of extension leads seemed highly unlikely to work.

However I remembered we had 2 60m lengths of orange circular 3 phase cable left over from replacing bore pumps. With the spare conductors doubled up and fitted to standard mains plugs we were good to go. Except with the two lengths laid out, we were still 20m short of the gate, so had to use a normal 30m extension cord to make the distance. So it was 150m in total, 120m being of low-resistance cable (measured about 1 ohm loop resistance) and 30m of 1mm2 standard extension cable (which would have added another 0hm or so of resistance).

End result worked perfectly - ran the welder in MIG mode and my mate was watching the voltage on a plug-in wattmeter I'd put in series. The voltage dropped to a minimum of about 210V (down from 245V) but I noticed no difference at all when welding - it's an inverter, so as the supply voltage dropped it would have cranked up the current consumption to maintain the power. The wattmeter showed a peak power of 3,000W.

Not something I'd do every day, but useful to know it's entirely possible at reasonable welding currents (I was set to about 18-20v, so 3,000W suggests it would have been peaking at about 150A minus losses).