Power mains question: wire gauge

DaveC · 2012-12-28T23:41:08+00:00

Air compressor 1/2 hp motor rated 220v (2-wire, not 3-phase) @ 15A. Distance from load panel ~100 ft (as the conduit runs). 15A can be handled by 14 gauge, but I'd normally go with 12 gauge due to start current. With such a distance, is it recommend to up-scale the wire to 10 ga? Thanks.

Dec 28, 2012 175 Replies

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gfretwell 13 years ago

OK you go by the nameplate rating. the conductor is sized to 125% of that. (you get 18.75a) The minimum wire size using 310.16 is 14ga. You can oversize the breaker to 250% of FLA so you could use a 37.5a breaker, that rounds up to 40a. per table 430.52 and 240.4(B).

Voltage drop is a separate issue

14ga wire with a 15a load 100 feet out drops 9.48v or about 4% of 240v. That is probably a little more than you want (more than the FPN recommendation). If you go up to 12ga you drop 5.9v (2.5%) so that is probably what I would do. You also will usually be fine with a smaller breaker than the max in 430.52 but there is a chance a 20a might nuisance trip.

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John Larkin 13 years ago

Well, then why stop at #6? Run 3KV and a distribution transformer. You never know.

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Michael A. Terrell 13 years ago

Who uses 3KV?

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krw 13 years ago

I've seen a *lot* of 1/2HP motors used for power tools that can be wired either way.

Rather irrelevant.

I always do it the right way. The "right way" depends on the situation. I guess the "right side" is universal, though, but it's also right.

It's a *lot* cheaper. #6 is a PITA to work with. No thanks!

Now you're throwing in random costs.

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krw 13 years ago

OK, 300K.

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John G 13 years ago

Bill explained :

The supply voltage has no bearing on the voltage drop. Only the wire size, the wire material, the run length (there snd back) and the load current affect the voltage drop in any line.

The supply voltage is required in those calulators only to allow the calculation of the percentage drop from the original supply not the actual volts lost.

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Tom Biasi 13 years ago

How about run what you need now with a pull string included?

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Michael A. Terrell 13 years ago

Inside your home? Or where you work?

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Michael A. Terrell 13 years ago

On an air compressor?

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krw 13 years ago

Sure. Most small fractional horse induction motors can be.

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krw 13 years ago

I think we have a winner!

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krw 13 years ago

Hey, you never know how big of a compressor you might need.

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rickman 13 years ago

100 feet of AWG 6 will set you back some C-notes. That's an expensive investment if you don't need it.

Rick

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Spehro Pefhany 13 years ago

It's also a sweaty PITA to pull.. ( I ran some to a manly (for single phase) compressor and kiln).

Best regards, Spehro Pefhany

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Jasen Betts 13 years ago

a larger compresser is likely to have a soft start where the pump compression is releived come on until it's up to speed.

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Jasen Betts 13 years ago

a larger compresser is likely to have a soft start where the pump compression is releived until it's up to speed.

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Michael A. Terrell 13 years ago

Those are toys, but they might be acceptable to amateur woodworkers. The ONLY thing I use a compressor that small for is to blow dust out of a computer.

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