My plasma cutter has a 3 prong 220V power cord.
I want to make an extension cable that I can plug into my dryer's 4 prong 220V outlet.
I have a 3 prong receptacle to put on the other end of my cord for the cutter. I have 3 conductor wire - two hots, a neutral, and a ground.
Can I wire this as a 2 conductor and just leave off the ground?
What Ed Beal says, but let me backfill some details.
Here is our cast of characters.
If you're confused about neutral and ground, perhaps it's the welder has a NEMA 10 connector. (Hot hot neutral). This was the standard dryer plug in the old days before safety was important.
For some strange reason a lot of people still use NEMA 10 plugs on welders.
Anyway, if your welder has a NEMA 10 plug, change it to a NEMA 6 plug (Hot-hot-ground) which is on the same shelf 2 bins over. Welders need ground if you don't like being dead.
Now it is a simple matter of getting “cordage” which is special flexible cable made for daily flexing - well you know, every one of your home appliances has cordage. Don't use Romex for this, it's not made to flex and will quickly get metal fatigue, crack, heat up, arc and start a fire.
You need 3-wire, which will be black white green wire colors. Here's the important part: mark the white wire black on both ends. It will not be used as neutral, but rather as second hot. (the two hots are interchangeable, you can use red if you want but it doesn't matter).
Also note that in European style cords, ground is yellow/green, hot1 is brown, and hot2 is light blue. (well they call that last one neutral, but in a North American context it's hot2 because of split-phase).
Ok, your plasma cutter is 220, well I will update you and say 240 as some like the modern voltage standards.
So you can use a 3 conductor cord, 2 current carrying conductors and the ground.
As someone else mentioned a 10awg cord is needed as dryers are 30 amp.
You do not need the neutral for your plasma cutter but you do need the ground.
