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I have an air compressor with a 240V 15A power requirement and a 6-20 plug (looks like normal US plug but with one of the flat ends turned at a 90 degree angle). Instruction manual can be found [here][1] (pdf hyperlink, 1MB).

I'm trying to figure out the best way to deliver power to it.

I have a gas powered generator that has a 120/240V 30A L14-30 twist lock outlet. Alternatively my house has a 240V 4 prong 30A dryer outlet (it's a 14-50 plug/outlet but is on a 30 amp breaker).

I'm looking for a quick and safe way to get the compressor up and running other than having an electrician put in an appropriate new outlet. Any ideas?

Info plate on motor attached.

[1]: https://c.searspartsdirect.com/mmh/pd_download/lis_pdf/OWNM/L0807019.pdfenter image description here

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Put a 30A cord on it

You should be able to remove the existing cord from the compressor and attach a 30A cord (10AWG cordage, either terminating in a 6-30 or a 14-30 with the neutral wire at the device end terminated in a way that won't short to anything, including the case) to the thing.

This is no different than putting a 15A cord on a 1A clock. The device itself is overload protected, and the breaker will protect the premises wiring from gross shorts.

While you're at it, you can fix the dryer so it uses the proper receptacle (14-30) instead of the 14-50 you say it's on.

  • I think this may be the easiest and cheapest solution. Is that what is meant by "thermally protected"? That the compressor motor is already overload protected? I obviously don't know much about this stuff (I know basic electromagnetic undergrad physics). In general, when can I tell if it's bad to plug a device into an outlet with a breaker above the device's draw? – jdods Jul 10 '17 at 0:51
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    @jdods -- my view is that it's basically never bad for the types of branch circuits found in residential work. Plugging a 1A device into a 200A industrial circuit might be a problem under certain circumstances due to fault current levels, but that's well beyond what we deal with here. And yes, the motor is indeed overload protected -- there is a device inside the motor that will trip and disconnect it if it stalls out/overheats. – ThreePhaseEel Jul 10 '17 at 0:52
  • I guess one question I have is what to do with the neutral wire as the compressor currently doesn't have one. Whether I plug it into the generator or the dryer outlet, the 4th neutral slot will be unused. – jdods Jul 10 '17 at 1:06
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    If you don't mind butchering the cord, you can cut the terminal off the neutral wire then insulate it with heat-shrink or electrical tape. – ThreePhaseEel Jul 10 '17 at 1:14
  • Thanks for the help! I think this and all the other comments and answers really help me understand. I think I can now get it rigged up safely at least for temporary use until I get a proper separate outlet hooked up. – jdods Jul 10 '17 at 1:26
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Actually, it is a fielder's choice.

Either way, all you have to do is make up a cord with #10 wire that is rated for 30 amps with a male plug on one and a female plug on the other to transition between the different plugs.

Good luck and stay safe!

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TLDR: you must follow the labeling or instructions on the motor or compressor. You can change breakers without changing wires.

The rules for 240V receptacles are exactly the same as for 120V receptacles:

  • cheater cords are out of the question.
  • labeling and instructions on an appliance must be followed.
  • if the breaker is 30A, only 30A receptacles can be used, and usually only one.
  • if the breaker is 15A, only 15A receptacle(s) can be used.
  • if the breaker is 20A, 15A or 20A receptacles can be used, but if there is only one receptacle, it must be 20A.

Plugging into the house wiring with a cheater cable is a no-no. The right way is to change the breaker to 20A then fit a NEMA 6-20 receptacle. You do not need to change the wire, you are always allowed to use thicker wire than the breaker requires. Obviously you will not be drying with electric at that point.

The problem is that the compressor could have a serious problem, and the breaker would not trip because it's too large. You need to follow the labeling or instructions on the motor or compressor.

I'm not sure if it's legal with a generator, it is certainly more common to hork things up with cheater cords. A generator is an expensive way to run a compressor.

  • Yes, running off the generator is not a long term solution. Thanks for the comments. I don't understand what a cheater cable is. How about this product? amazon.com/gp/aw/d/B004XWAKUQ/… – jdods Jul 9 '17 at 22:27
  • Actually, a 30A breaker might be A-OK on such a circuit provided Art. 430 allows it and the motor's internally protected... – ThreePhaseEel Jul 9 '17 at 22:35
  • @jdods on the Amazon item, note the "ships from and sold by (someone other than Amazon)”. That is called the Amazon Marketplace, and is just as bad as eBay and AliExpress in terms of being rogue sellers who will sell you anything. The bottom line here is what your local AHJ says. So stop by your town's permits office and ask when the electrical inspector is around. I would not expect him to say yes, but he has a town full of RVers, recovery cleaners and floor finishers who do it all the time, so maybe. – Harper Jul 9 '17 at 23:19

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