Wiring 7.5 hp compressor ?

[toms73novass]

I will be needing to wire a 7.5 hp compressor in the near future and I want to get an idea of the wire that I should use. From reading other posts I figure that I will use a 50A breaker and #6 AWG wire.

The question is, what is the proper type of wire to run for something this large? I am use to running 14 or 12 awg NM wire nothing of this size. Would I be running thhn wire inside of an armored cable or is there a cable similar to NM that is used for applications like this? I would like to have some knowledge of the wire that I want before I go to the supply house.

Thanks

 

[wilbilt]

You can do it either way. #6 is available in a "giant Romex" type cable.

 

[LoneGunman]

6/2 romex would be my choice

 

[Stuart in MN]

What voltage are we talking about? 240volts single phase, or some sort of three phase power? For 240volts single phase, the full load amp rating is going to be around 40 amps (that's based on the charts in the NEC codebook, the actual value will be on the motor nameplate.) The wire and overcurrent protection (circuit breaker) should be sized at least at 125% of the full load amp rating, or 50 amps minimum. #8 copper wire with insulation rated at 75 degrees C is good for 50 amps, but this is right at the limit so based on the limited information I'd go up one size to #6 which is rated for 65 amps. This is also assuming the distance from your circuit breaker panel to the air compressor is less than 100 feet or so, if it's much more than that you'll have to evaluate the voltage drop and possibly go even larger.

The compressor will need a magnetic motor starter; I assume it will come with the compressor, or otherwise you'll need to provide one. You'll need a disconnect switch as well, mounted within sight of the compressor.

If this is a new compressor, the recommended wiring should be covered in the owner's manual.

 

[Roospike]

I ran #6/2 copper (11' long) wire with an 80 AMP breaker for my IR 7.5 hp compressor. Running amps is 33 on the motor , compressor is rated at 40 amp and the starting draw is around 74 amps .

It was $5. more for the 80 amp breaker over the 50 amp .