Just wondering what is the proper way to hook up a 3 prong 240v outlet like a nema 6-50 using 6/3 with ground romex for a welder or air compressor to a 4 wire seperated neutral and ground bus sub panel.I know the black and red hot leads but do you use the white wire for the ground prong or do you use the smaller ground wire. I assume you use the white to the neutral bus and the ground to ground the box to the ground bus seeing as the box is metal.
Thanks for the help.
For a straight 240V receptacle (3 prong) you would not have a neutral, only two hots and a ground. If the 6/3 is already run, cap off the white at each end, connect the hots to the breaker and the bare copper to the grounding bus. If the wire has not been run, you can use 6/2 instead of 6/3.
"Life is hard. Life is harder when you're stupid." John Wayne
If the device truly is a 240 volt appliance and not 120/240 then the 3rd wire connects to the ground bar not the neutral. If it's 120/240 the plug should be a 4 wire plug, not a 3 wire. Most welders however are only 240 volts and do not require a neutral connection (just need an equipment ground).
The way I have always noted the plug configuration to be (in a 3-wire plug):
If the 3rd blade is flat its a 50 amp plug requiring a NEUTRAL connection to the 3rd blade. If its a right angle its a 30 amp plug requiring a NEUTRAL connection. If the 3rd blade is a round pin or a U shaped pin it is a ground only connection and usually amperage is determined by the configuration of the blades (size and position, etc).
4 wire plugs have both the neutral and ground pins in the plug, so the blade that is either flat or right angle in the middle is the neutral and then the pin that is either round or U shaped is the ground, leaving the remaining two conductors (on the outer edge) as the 2 hots.