Need help on how to wire 240 volt machines


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.

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
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You only needed to run three wires to this particular machine

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snipped-for-privacy@gmail.com wrote:

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]

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.

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

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.

It will be, if you wire the receptacle correctly.

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)
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Excellent. Thanks very much for your response. You really made it clear for me.
And i do plan to run several 120 circuits of the panel too.
Again, thanks a lot. Tim
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snipped-for-privacy@gmail.com says...

Thanks.
You're welcome. Glad to help.

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Yeah, i am. I understand the 120 volt thing. I think. So why does 240 volt not require a neutral? I thought everything electric was based on supply (hot) and return (neutral). Ground was only for when the shit hit the fan, and the power had to decide between your body or the easier path to earth which was the green wire.
Why is 240 different than 120 in that sense?
And why is it said that one should run 4 wire if its a 240 appliance?
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snipped-for-privacy@gmail.com wrote:

You're correct that everything needs a complete path. With 240V in North America, you can think of it as one hot being at 120V and the other at -120V. The difference between them is 240V.
If you only need pure 240V, then you don't really need the neutral--you just use the two hots and ground. Current flows in one hot and out the other, and the ground is for when things go wrong.

Many 240V appliances in North America use 120V control circuits. This requires a neutral conductor. The main load of the appliance uses the two hots, and the ground is still for when things go wrong.
Chris
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I had no idea. Honestly, what i've learned in this post gave some bills to my electrician. Don't want to touch it.
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On 31 Jan 2007 01:19:24 -0800, snipped-for-privacy@gmail.com wrote:

NEMA 6-50 is 240V with ground 50A. This is for 240V only, and has no neutral.
--
Mark Lloyd
http://notstupid.laughingsquid.com
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