Power mains question: wire gauge

Dec 28, 2012 175 Replies
M

I've never seen a 240 volt compressor it a 1/2 HP motor 2 HP is common, and go on up as the capacity increases. A local business recently switched from multiple 2 HP 240 VAC 60 gallon compressors to a pair of 480 VAC three phase units with 120 gallon tanks that are set upi to run their entire production line from one unit. It was the old EDCO factory that Emerson closed a few years ago..

Cheaper? When did yo go over to the 'Do it any way but right' side?

It's not cheaper when the extra labor and increased material costs are added for doing the job more than once. If you didn't size the conduit for more wire, you'll have to rip it all out & start over.

Then there's the cost of a bribe to get the inspector to look the other way.

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G

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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J

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

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K

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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J

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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T

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

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M

Inside your home? Or where you work?

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M

On an air compressor?

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K

Sure. Most small fractional horse induction motors can be.

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K

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

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R

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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S

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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J

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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J

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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M

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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M

The suggestion was to put in a sub panel, if there is a likelyhood of more tools that require 240.

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M

How much wire have you pulled?

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