wire sizing

[bucketman23]

im having a debate with my father over a wire sizing issue and need some clarity. he is feeding a piece of equipment and is installing a single 125A 3phase 208v circuit. the argument is number 1 or number 4 wire. i say number 1 to feed he says the breaker will hold no larger than number 4. i have not seen the equipment or the breaker in question just going from my head and the info he gave me over the phone.

 

[charlie b]

A #4 does not have enough ampacity to be protected by a 125 amp breaker. I agree with you, in this respect. But things change a bit, when you are feeding motors. What kind of equipment is this, and does the nameplate or other manufacturer's information give you a wire size or breaker size?

 

[mtbkl]

im having a debate with my father over a wire sizing issue and need some clarity. he is feeding a piece of equipment and is installing a single 125A 3phase 208v circuit. the argument is number 1 or number 4 wire. i say number 1 to feed he says the breaker will hold no larger than number 4. i have not seen the equipment or the breaker in question just going from my head and the info he gave me over the phone.

No larger than a # 4 THWN on a 125A bkr? I doubt that. :-? Go take a look and still in doubt, look up the bkr in the manufacture?s catalog. According to Sq D catalog; a typical 100 amp, molded case ckt bkr has a wire range of #14 or #12 to #1/0

 

[infinity]

Why would a 125 amp CB only take a conductor capable of carrying 85 amps?

 

[tryinghard]

You need to check out table 310-16 & 240-4. At a glance you may be okay with #2cu THHN 75 degree, 125A is the load you conductors have to carry.