DIYbanter - View Single Post - Need help on how to wire 240 volt machines

Doug Miller

In article .com, wrote:

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.

The first thing you need to understand is that a pure 240V circuit, in the
United States and Canada, _does_not_have_a_neutral_ .
[snip]

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?

Incorrect assumption. The two flat prongs are indeed the two hots. The round
one is GROUND. There is no neutral, and you do not need one.

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.

Because you misunderstand how 240V circuits work. Three conductors --
black, red, and *bare* (or green) -- would have been enough.

What do i do with the bare wire?

Connect it to the grounding terminal on the receptacle, of course, and to the
grounding busbar in the subpanel.

You're asking the wrong question, though. The right question is, what do I do
with the *white* wire? The answer is: Put a wire nut over each end of it. You
don't need it. Or, if this is run through conduit, pull the white wire out.
You don't need it.

Will my machine be grounded?

It will be, if you wire the receptacle correctly.

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.

Good for you! Far better to ask, than to assume and do it wrong. The bottom
line is, neither your plasma cutter nor your compressor requires a *neutral*.
They both require a *ground*. So in the receptacles for both of them, you
connect the ground. There is no place to connect the neutral, so you don't
need to run four wires to the receps -- three will do.

At this point, you're probably wondering why you bothered running four wires
to the subpanel, if all you're going to need is three. The answer is, so that
you can run 120V circuits off that subpanel, too -- they need the neutral,
even though the 240V circuits don't. Maybe you don't ever plan on putting any
120V circuits in that panel... but the next guy to own your home might.

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.