Table 430.52

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624

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If I have a moter FLC 10hp 208 volt is 30.8, sizing inverse time breaker 2.50% table 430.52.
FLC 38.8x2.50%= 77 amps next size up 80 amp. My wire size would be FLC amps 30.8x1.25=
38.5 number 8 awg wire, I’m I doing this right it seems wrong 8 awg wire on a 80amp breaker?
 
624 said:
If I have a moter FLC 10hp 208 volt is 30.8, sizing inverse time breaker 2.50% table 430.52.
FLC 38.8x2.50%= 77 amps next size up 80 amp. My wire size would be FLC amps 30.8x1.25=
38.5 number 8 awg wire, I’m I doing this right it seems wrong 8 awg wire on a 80amp breaker?
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Read 240.4, then 240.4(G) and Table, then back to the appropriate part(s) of 430.
 
Remember that your motor will have overload protection so the wire is protected. The breaker is there for short circuit or ground fault protection only.
 
Larry sent you to the appropriate code section to tell you that the answer to your question is yes. Dennis told you why. I thought I would let you know because sizing a wire that way is scary until you know you are right. I have only seen an engineer size a motor feeder to these tables a couple times in my career. They usually size them to the feeder breaker. A similar over-engineered thing is the size grounding electrode conductor (250.66) for a concrete encased electrode our a pair of ground rods.
 
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