For 220, Do I use neutral or ground


Old 05-08-08, 01:07 PM
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For 220, Do I use neutral or ground

Thanks in advance.

I am running new wire to my air compressor. It is 230v 15 amps. The outlet has 3 screws, 2 brass and 1 green color.

I had the compressor wired with 8 gauge, but the wire is too fat for the outlet and it was temporary just to get the compressor running. So now I want to make it correct. But I ran into a question. The 8 gauge I was using is 3 wires, 1 black,1 red and 1 white. So I was using the white as neutral. But I read on this forum that maybe it should be wired with 2 wires 110v and a ground. But to me it seams wrong to have 220v continuosly returning back to ground. Should not it go back to the source?
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Old 05-08-08, 01:40 PM
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You have a pure 220v from the sounds of it. There is no neutral in this setup. You don't have 220v on the ground.
Old 05-08-08, 01:45 PM
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For a 240V compressor, you use two hots and a ground. You can install this with 12/2g cable if the distance is reasonable. Use the black as hot #1, color the ends of the white with a red marker and use that as hot #2, and the bare as ground. The breaker should probably be a 20A double-pole, but could be larger based on exact specs of the motor.
Old 05-10-08, 03:48 PM
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Everything that ibpooks said is correct but I want to explain how he came up with his answer. From your post I think you are a relatively new and inexperienced DIY electrician so knowing how to select the proper size conductors and OCPD's (Over current Protection Devices) or CB's is critical to your safety and success. But before I start let me say that the most important tool in any electrician's toolbox is an up to date copy of the NEC (National Electric Code). The NEC book is an expensive book, but it is essential to have one. Now to the problem at hand.

The size of the conductors one needs for a given circuit depends on the load applied to that circuit. In your case, the FLA (Full Load Amps) of your compressor is 15 Amperes. Now, referring to Table 310.16 of the NEC we find that a #12AWG Copper conductor can carry up to 25 Amperes which is sufficient for our load of 15 Amperes. The notes to Table 310.16 also tells us that circuits wired with a #12 AWG Cu (copper) conductor must be protected with an OCPD rated no greater than 20A.

A 220V. circuit does not required a neutral since the load is connected directly across the two hot conductors. If you are working with a 12/2 w. Gr. cable which is normally used for wiring 110V circuits that consists of one hot (black) conductor and one neutral (white) conductor, the neutral conductor is identified as the second hot conductor by painting it red or taping it with red tape. The code permits this use of the white conductor as long as it is identified wherever it is exposed, at both the panel end and at the load end, as well as where it passes through any junction boxes. At the panel end, both the black conductor and the identified white conductor connect to the two-pole CB.

A two-pole CB is used because the code requires that both legs of a 220V circuit be broken at the same time. Two single-pole breakers could be used side by side if an approved handle tie is used.

I hope that this information helps.
Old 05-10-08, 05:31 PM
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What Mr. Fixit43 didn't explain to you was "why" a 240 volt circuit requires no neutral. Since the two hots cross sine waves at the same time, one going up and the other going down. It is at this point one leg dies and becomes a neutral, and the other dies during the next cycle. Now this happens 60 times a second, so don't look for it except with an oscilliscope. Very cool to watch it happen, though.
Old 05-11-08, 08:37 PM
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Every circuit requires two wires. It doesn't matter what names that we humans attach to these wires. "Neutral" and "hot" are just words, and the electrons could care less what the wires are called.

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