My building is 3 phase. How do I go about wiring a 230V receptacle? (1 phase) It is the Hobart 187 Mig. Do I need to put a brand new circuit in and wire in a new receptacle? The 3 phase/1phase has me confused. I bought the building off my uncle. He said there is a 220v outlet in here but he pulled the breaker for some reason. I have 2 service panels. The one large one my 3 phase compressor is wired to. Then there is a panel that comes off this panel. There is a double pole 50amp breaker sitting on top of it. There is a receptacle hanging out of the box that I think may be 220v. It has a twist lok type plug in. I only see 2 wires. One, is connected to outlet then the other is grounded to the box. I don't see the other hot. Could this be it? If so I can just buy the correct receptacle and wire it in? Thx. Sorry for the long post. I appreciate it.

O.K. the one wire is neutral going to neutral/ground bus and the other is the ground going to neutral/ground bus. No other wires. The white is connected to the receptacle and the ground is coming straight from the neutral/ground bus and grounded to metal box. I would need a red and black wire correct? I know to connect them to each pole of breaker. Where to connect to on receptacle?

Any outlet will use brass terminals for the live wires, silver for a neutral if needed, and always have a green screw for the equipment ground.

A single phase 240 volt outlet will have two brass terminals and a green screw.

A 3 phase panel has 3 live legs. Your panel should be 120/208 volts, not 220 volts.

A 2 pole breaker for a 208 volt outlet will connect to only two of the 3 hot legs, providing 208 volt single phase.

Between each of the hot legs and the neutral will be 120 volts.

Does this answer your question?

What size breaker do I need to run? The receptacle states 50amp 250v. Does that mean I have to run a double 50amp? I had another response elsewhere stating I could run a double 30amp but I could run bigger if I ran larger wire. Which breaker should I run?

I am not sure what size breaker and wire, as you did not state what the unit needs. What does the nameplate say on the welder?

130 A @ 21.5 volts DC, 30% Duty Cycle At 60 Hz Input- 20% Duty Cycle At 50 Hz Input
20.5 Amperes

Minimum #10 wire on a 30 amp circuit is fine for the feed to this welder.

Thx so much for all your help. I appreciate it.