Cannot use #10 on a 35 amp breaker?

[twada]

NEC 240-3 d states that OCP cannot exeed 30amp for #10 copper. Does that apply for 90 degree insulation too? Why does Table 310-16 indicates that the ampacity of #10 is 35amp, and cannot use this on a 35amp breaker?

 

[lectro]

Re: Cannot use #10 on a 35 amp breaker?

art.240-4(d)is the rule of thumb to apply to most general over-current protection situations.however it also states that 240-4(E,f,g)also apply which the most common exception would be found in arts.430&440.also keep in mind that you can't use the 75&90 degree ampacities unless all associated equipment and terminations are also rated accordingly.

 

[twada]

Re: Cannot use #10 on a 35 amp breaker?

240-3 e regarding tap conductor.
Are the branch feeders from panelboards considerred as tap conductors per NEC's definition?

 

[lectro]

Re: Cannot use #10 on a 35 amp breaker?

to answer your question,no.i believe you need to cross reference arts.210-20(b)&210-24 to answer your question.also your code reference indicates you are still using nec 99,my code reference is from nec 2002.

 

[don_resqcapt19]

Re: Cannot use #10 on a 35 amp breaker?

You use the 90?C ampacity for derating purposes.
Don

 

[bennie]

Re: Cannot use #10 on a 35 amp breaker?

twada: Are you asking why have a 35 amp breaker, when there is no 35 ampacity wire?

 

[iwire]

Re: Cannot use #10 on a 35 amp breaker?

Originally posted by twada:
Why does Table 310-16 indicates that the ampacity of #10 is 35amp, and cannot use this on a 35amp breaker?

310.16 rates 10 AWG copper 40 amps at 90C and 35 amps at 75C because that is the rating of the wire.

240.4(D) is a separate issue that requires 30 amp overcurent protection for 10 AWG in most instances.

There are times where you may use 10 AWG for greater loads then 30 amps, look at Table 240.4(G) Specific Conductor Applications for when we can do this, as has been said motor loads are one of the time you may have a breaker larger than 30 amps on 10 awg.

And as Don pointed out you may use the 90(C) rating of 40 amps for derating purposes.