dhalleron
Senior Member
- Location
- Louisville, KY
I'm a little slow when it comes to motor circuit sizing.
I have a friend that had a 2 HP air compressor on a 20 amp 230 volt circuit in his residential garage. He upgraded to a 5 HP air compressor and is tripping the breaker.
I haven't been there yet and don't know the exact name plate info. From what he tells me it's installed in UF cable on #12 wire that runs under some concrete and can't easily be replaced. He wants to just increase the size of the breaker.
NEC 2008
Table 430.248 tells me a 5 HP motor draws 28 amps
Table 430.52 tells me the max Short-Circuit protection is 250% of 28 amps or 70 amps max breaker
Table 310.16 tells me #12 can handle 25 - 30 amps depending on the insulation.
I know I can size the breaker more that the current carrying capability of the wire for a motor. What I don?t know for sure is what current to figure the motor actually draws and what the #12 UF can handle.
This air compressor might be pushing the limit of #12 UF if I understand this right. Any pointers such as a duty cycle thing I am missing that might save the day?
Thanks,
I have a friend that had a 2 HP air compressor on a 20 amp 230 volt circuit in his residential garage. He upgraded to a 5 HP air compressor and is tripping the breaker.
I haven't been there yet and don't know the exact name plate info. From what he tells me it's installed in UF cable on #12 wire that runs under some concrete and can't easily be replaced. He wants to just increase the size of the breaker.
NEC 2008
Table 430.248 tells me a 5 HP motor draws 28 amps
Table 430.52 tells me the max Short-Circuit protection is 250% of 28 amps or 70 amps max breaker
Table 310.16 tells me #12 can handle 25 - 30 amps depending on the insulation.
I know I can size the breaker more that the current carrying capability of the wire for a motor. What I don?t know for sure is what current to figure the motor actually draws and what the #12 UF can handle.
This air compressor might be pushing the limit of #12 UF if I understand this right. Any pointers such as a duty cycle thing I am missing that might save the day?
Thanks,