i recently got an older all star wire feed welder. im looking at the plug . its 240 volt.  but the wiring has 3 wires black , white and green. the green wire is grounded to the welder inside the box. the black is fused and white runs to parts unknown.  this goes against what i know about 240 wiring as there  appears to be no return wire for 240. is the return through the ground ? is this old style wiring system ? pre safety grounded? or am i missing something? also it says 100 amp on the welder. if i do use this thing what would be a good amp circiut breaker for it? also the power cord appears to be nothing more than extension cord gauge 3 wire  ? dont want to burn down the garage but i do know the welder was working at previous owners house who is long gone now.. thanks for any help or input?

Look at the name plate on the drive motor (every electric motor has a nameplate). It will list the phase, voltage, amperage, and RPM. I really have a hard time believing it is 240 volts.

Al

Older 220/240V Systems used the "Two Hots and a Ground" style wiring. Generally it would be Black and Red for hots and Green/bare for ground, but Black and White would sometimes be used for the Hots. This would be single phase.

Not sure when the change happened with using the "Two Hots, Neutral/Return and Ground" that is currently 'Code'. But I know my 30 year old house has 'Two Hots and Ground' for the electric dryer, and the brand new dryer I bought is 'Two Hots and Ground"

As for the size of the wire, the charts online say 1 AWG copper wire for wiring to the box, the cord would probably need to be the same.

*I'm not an electrician, just going by what I've seen*