I had my workshop wired by an electrician a while back and had him rough wire an outlet for a welder in the eventuality I would get one. The time has come and the new MM 180 will be here on Monday. The electrician had done everything but install the actual plug and had covered the outlet box with a solid cover and had marred the end of the wires. I went out this AM and bought a welding 250v plug and decided to install it but the plug has room for 3 wires (grd + 2 wires) and the installed wire contains 4 (grnd+3 wires). Which 3 do I use on the plug ? The elctrical box has the red and black wire fastened on the breaker, the groung where all other grounds are and the white is where all other whites are. Is it possible that the electrician only needed a 3 strand wired and only had a 4 strand wire on hand ? Asside from taking a part my dryer outlet to see how this is done can any of you help me out ?

Thanks JC