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Old 09-28-2009, 01:34 PM   #1
 
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Breaker / Cable Recommendation for Air Compressor


I have an Ingersoll Rand T30 7.5 HP 80 Gallon Compressor that runs on 230 volts and requires 32 Amps Single Phase. I have 100 watt service running to the house and a 2 pole box.

What size circuit breaker / cable is recommended?

The compressor came installed with a cable that unfortunately is not long enough. I plan on swapping out that with a new, longer, cable. Between the compressor and the box I will have approximately 60 feet of length.
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Old 09-28-2009, 08:07 PM   #2
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Originally Posted by electric00003 View Post
I have an Ingersoll Rand T30 7.5 HP 80 Gallon Compressor that runs on 230 volts and requires 32 Amps Single Phase. I have 100 watt service running to the house and a 2 pole box.
That is pretty good size unit there I will have more info below text so read on ,..

Quote:
What size circuit breaker / cable is recommended?
That compressor you will need at least 50* amp breaker with #8 THHN's in the conduit or 8-2 NM cable.
Quote:
The compressor came installed with a cable that unfortunately is not long enough. I plan on swapping out that with a new, longer, cable. Between the compressor and the box I will have approximately 60 feet of length.
The best way you do is hard wired to the receptale or hardwired all the way thru the contractor or pressure switch { depending on the set up I know for this size useally go to the contractor first }

As I mention 50 amp breaker that is the normal breaker I useally deal with this size of compressor unit however the NEC code do have specal code it can use much larger breaker but only with hardwired no cord / plug set up with direct hardwired units it is stated in NEC code Art 430

But before you do that what else hevey electrical load you have on the house at the moment ?

Merci,Marc
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Old 09-29-2009, 07:26 AM   #3
 
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Thanks for the reply Marc.

I was told by the person I purchased the air compressor from that it draws 40 amps on start-up even though it is rated at 32 amps on the label. Do you still think a 50 AMP breaker will do it?

I know the code states that you should use 250% of the rated AMPs so going by these standards, I would require an 80 AMP breaker even though I think it is overkill.

Currently the house has the standard Stove/Microwave/Dishwasher/Washing Machine/Dryer/AC's. As long as one of the larger AC's that runs on 220 does not run at the same time as the compressor, I should be good.

I plan on hard wiring the compressor directly to the breaker box, this is how it is setup now but the cable is not long enough for my application so I will have to swap it out.
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Old 09-29-2009, 10:55 AM   #4
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Originally Posted by electric00003 View Post
Thanks for the reply Marc.

I was told by the person I purchased the air compressor from that it draws 40 amps on start-up even though it is rated at 32 amps on the label. Do you still think a 50 AMP breaker will do it?

Maybe, but I doubt it. This motor should draw around 40 amps running, not starting. It will draw up to 8 times the running current when starting. So I think you are pushing the envelope with a 50 amp breaker. But it could be worth a try should you have a 50 amp breaker lying around.

I know the code states that you should use 250% of the rated AMPs so going by these standards, I would require an 80 AMP breaker even though I think it is overkill.

That is correct. Table 430-152 says 250%. So its FLA x 2.50 = breaker size.

Currently the house has the standard Stove/Microwave/Dishwasher/Washing Machine/Dryer/AC's. As long as one of the larger AC's that runs on 220 does not run at the same time as the compressor, I should be good.

You will find out soon enough.

I plan on hard wiring the compressor directly to the breaker box, this is how it is setup now but the cable is not long enough for my application so I will have to swap it out.
Run the circuit to a small disconnect and install a whip to the compressor. You will need #8. This is an instance when you can use wire that would normally be to small for the breaker. So #8 on a 80 or 100 amp breaker is compliant.
My book says your motor will draw 40 amps running (FLA). If this is the case, you can use up to a 100 amp breaker.

ps......Sorry i just noticed the motor is marked for 32 amp. 80 amp breaker is the largest you can use.
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