Hello

I need some on understanding some basics on how to wire a 240 volt 40
amp Hypertherm Powermax 600 plasma cutter and a 240 volt 20 amp air
compressor to be exact.

First, let me describe my power supply situation.

I had an electrician recently upgrade my main panel and service from
100 amp fuse to 200 amp breakers.

My intention is to get a 100 amp sub panel in the attached garage on
the opposite side of the house.

From the main panel I ran 2-2-2-4 AL wire out the basement level, up
the out side of the house, back inside through the attic and across
the length of the house where it drops down into the attached garage
to feed a 100 amp sub panel. Total length of the wire is 80 feet.

The 2224 wire meets a 125 amp main lug sub panel in my garage. As i
was told, my ground and neutral are isolated. I installed the
supplied Ground bar, as the instruction book said if i was using it as
a main lug. Everything in the sub panel is how it should be.

My question comes in here... My plasma cutter has a NEMA 6-50 plug pre-
installed. It looks like a standard 120 plug, only bigger. Thats 3
prongs.

So i went to Home Depot and purchased a NEMA 6-50 outlet. What
confuses me, is that its only 3 prongs. I assume its supposed to be
the two hots are the narrow prongs, and the round one is supposed to
be the neutral? So how is it grounded?

I realize way back at the main panel the ground and neutrals are
connected.

So why did i bother to run 4 wires of 8 gauge (black, red, white,
bare) if i'm only using 3 of them. What do i do with the bare wire?
Will my machine be grounded?

I realize this will appear trivial to most electric guys on here, but
i just don't get it. I've looked quite a bit on the internet and
havn't found a clear answer. I paid too much money for the plasma
machine, and i don't really want to die, so i figured i would ask.

Thanks folks,
Tim