wire size for large air compressor


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Old 01-31-14, 06:21 AM
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wire size for large air compressor

I'm moving a large 220 single phase air compressor to about 100-120 ft from the breaker box. I check and it currently pulls 23 amps on each leg as it is running. So I need to make sure I buy large enough wire. I'm thinking that I need for the 2 hot and neutral size 8 and for the ground size 10. Also the next part I think a 3/4 gray pvc conduit is sized correct for this run. Thanks for any help.

David
 
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Old 01-31-14, 07:39 AM
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If you are in the U.S. it is 240 volts and no neutral is used on a 240 volt only circuit. So two #10 hots and a #10 ground. ĺ" PVC conduit will be large enough. You can upsize the hots if you want to #8 but voltage drop on #10 is only ~5 volts.
 
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Old 01-31-14, 09:49 AM
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The calculator I use said
1 conductors per phase utilizing a #10 Copper conductor will limit the voltage drop to 2.42% or less when supplying 23.0 amps for 120 feet on a 240 volt system.
 
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Old 01-31-14, 12:39 PM
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I'm moving a large 220 single phase air compressor to about 100-120 ft from the breaker box.
What is the horsepower? Motor circuits are sized and protected differently than typical branch circuits.
 
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Old 02-01-14, 05:50 PM
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Motor Circuit Size

As pointed out by Casualjoe motor circuits are sized differently. I'm not near a code book but if I recall correctly, You size the conductors based on the ampacity from the NEC Tables for the H.P. of your motor. The motor nameplate ampacity is used to determine the size of the overload protection. The Overcurrent protection could go as high a 250% depending, to handle the starting current. Since your just moving the compressor it probably already has its overload protection so you just need to check the code tables to get the current and then size the conductors for 125% minimum. You do not need to use the 125% ampacity for your voltage drop calculation.
 
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Old 02-01-14, 06:31 PM
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NEC rules for a 3 horsepower motor at 240 volts (single phase) call for a full-load current of 17 amperes. For a 5 horsepower motor the amperage jumps to 28. That tells me that this is likely a "compressor duty" motor on a home shop air compressor with a rating of maybe five horsepower.

Not a very large compressor at all.
 
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Old 02-01-14, 07:08 PM
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Not a very large compressor at all.
Probably a large tank.
 
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Old 02-07-14, 02:42 AM
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Probably a large tank.
Nah, a "large" tank would be in excess of 1,500 gallons. Most of my compressors where I worked had 1,500 gallon receivers. When the one plant was upgraded they added a 5,000 gallon receiver and then made an "augmentation" station with a pair of 75 CFM rotary machines (rubber band drive ) discharging to a 30,000 gallon receiver.

I once had the company purchase an air-powered vacuum cleaner to use in boiler cleaning. The vacuum company rep tried to dissuade me from getting the twin-venturi model stating it really took a lot of air. When I told him I had 21,000 CFM of compressor capacity he stopped trying and accepted that I knew what I was buying.
 
 

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