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I am installing a new compressor in my garage. I already have 240V installed to run a kiln. The kiln is only used maybe 10 times a year. My thought is to splice into the 240V line to the kiln to run the compressor which is also 240v. The kiln is wired with 10/3 off a dual 30A breaker. the compressor needs 12/2 and pulls 15A.

What is the best way to do this?

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If the compressor is running off 12/2, then it's 120 v. – Chris Cudmore Mar 15 '13 at 16:34
Its more likely he was right about the compressor being 240 and wrong that it "needs" 12/2 vs 12/3 – HerrBag Mar 15 '13 at 18:59
Of course, we're assuming North American wiring. – Chris Cudmore Mar 15 '13 at 19:28
It is 240v and in North America. The owner previously use wire with a Black, White and copper wire. I thought this was 12/2 wire? – Jack Mar 15 '13 at 20:34
At this point, I can't tell what's going on, and withdraw all advice. Something's not standard here, and I think you should call an electrician. – Chris Cudmore Mar 15 '13 at 22:29

A simple solution would be a specialty extension cord like this:

enter image description here

It's hard to see from this pic, but it's a 240 v Male, with several 120v outlets on the other end. You could plug it in where the kiln is, thus ensuring both can't be used at the same time.

Made by Ericson. But the low end one is $350. You might be better off to run a new circuit.

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Great Idea Chris!!! Problem solved. Cudos – shirlock homes Mar 15 '13 at 19:55
Not really. At $350, I can get a lot of electrical work done. – Chris Cudmore Mar 15 '13 at 20:05
depending how far the kiln is from the compressor, one could build a cord similar to this for a lot less. Still think it's a good idea. – shirlock homes Mar 15 '13 at 20:14

Since the compressor is 120vac @ 15Amps, there is not a correct way to wire it directly off the kiln circuit. The compressor would be way over-fused on a 30 amp circuit. The correct way would be to take the 10/3 feed into a small subpanel and fuse the kiln and compressor separately in that panel. Of course the best way would be to run a 12/2, 15amp feed from the main panel to the garage for some 15A and possibly 20amp outlets. 12/2 would be fine, even though one size larger than needed unless it is a long run.

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Maybe Tester can check the NEC requirement for the sub-panel. – shirlock homes Mar 15 '13 at 15:15
My gut tells me if you wanted to use a subpanel, you'd have to bump the feeder up to #8 and use a 40A breaker in the main panel. Then you'll use a 30A double pole breaker in the subpanel for the kiln, and a 15A single pole breaker for the compressor. But there is no way to know for sure without more detail about the equipment. – Tester101 Mar 15 '13 at 15:24
I'm not sure if there is percentage the sub-panel has be be above the sum of the sub circuits – shirlock homes Mar 15 '13 at 15:37
Is there any type of breaker that will flip circuits -- Ensuring the compressor and kiln can't be used at the same time? – Chris Cudmore Mar 15 '13 at 15:44
@shirlockhomes It would involve knowing nameplate values on the equipment, and doing some math. Not likely a guessing game, or blanket case. – Tester101 Mar 15 '13 at 15:57

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