Dwelling Garage Air Compressor Calc

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WadeC

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Location
Texas
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Electrician
Do I have this right? For a 7hp 1phase 240v dwelling garage compressor, not within line of sight I would need a 50Amp conductor and a 70amp breaker with a fused disconnect with 70amp time delay fuses?
 
It is unlikely that you really have a 7hp motor. Look at the motor nameplate for the actually current. The 7 hp is very likely some type of "marketing" horsepower, such as "peak horsepower" and not a real number.
 
don_resqcapt19 said:
It is unlikely that you really have a 7hp motor. Look at the motor nameplate for the actually current. The 7 hp is very likely some type of "marketing" horsepower, such as "peak horsepower" and not a real number.
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I thought it seemed high. The owner told me it was 7hp. I told him I wanted to see the nameplate but the compressor is in another state. Did I use the correct calc?
 
don_resqcapt19 said:
It is unlikely that you really have a 7hp motor. Look at the motor nameplate for the actually current. The 7 hp is very likely some type of "marketing" horsepower, such as "peak horsepower" and not a real number.
Click to expand...
you were right. Nameplate says HP: Spl and Amp: 15
 
WadeC said:
you were right. Nameplate says HP: Spl and Amp: 15
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Yeah those numbers are normally fudged. Does it also say 240 volts? According to T430.248 a 1 HP motor at 120 volts is about 16 amps. A 3 HP at 230 volts is 17 amps.
 
This motor likely will run on a 20 amp breaker with little or no trouble. And should even be able to use 14 AWG conductor as long as is not one required to use 60C ampacity table, which would include NM cables.
 
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