I am running 240 for a shop air compressor. It is a single phase. I need about 50 ft of wire to make the run. What size wire? I

What is the load?

45 on start up

14.7 amps

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#12 on a 20A or 25A breaker.
You can even use #14, but I typically don't wire things like tools, machines, etc, with less than #12.

Who told you you needed #6?

Nobody I just thought I needed a 60 amp breaker to run the compressor. I was told the compressor will pull 45 amps at start up.

Not necessarily. Motors are a strange breed of animal. All motors have an in-rush amperage that can be quite high, but not adversley effect the breaker. The wire from the breaker to the motor should be sized at 125%.

For example, you need to get the full load amperage required by the motor. You can get that from the tables at the end of NEC Article 430 if that is not on the electrical specs with the motor. Then multiply the FLC by 1.25 to get your operating amperage.

14.7 FLC X 1.25 = 18.4 (rounded up)

A 12 AWG wire is listed for up to 20 amps. So as instructed earlier, it is safe for use.

Turn your attenion to the breaker, you need to size the breaker or fuse for this circuit so that it can handle the inrush current without tripping the breaker or opening the fuse. THis information is also in Article 430. Sorry but I don't have my copy of the NEC handy at the moment so I cannot give you info on the correct size.for the fuse or breaker.

Check the electrical specs that came with the unit, they should have the information you need there.

Nobody I just thought I needed a 60 amp breaker to run the compressor. I was told the compressor will pull 45 amps at start up.No offense, but this is a perfect example of why you should have a good idea of what you are doing before you do it.

I'm glad you are asking now and not after.