table 310-15(b)(2)(a)

[sokkerdude]

Article 310(b)(2)(a) Where the number of current-carrying conductor in a raceway exceeds three, the allowable ampacity of each conductor shall be reduced as shown in Table 310-15(b)(2)(a). Using this adjustment factors could someone tell me how many #12 THHN current-carrying conductors can be in a 2 in. conduit and going to 20 amp curcuit breakers. Please explain everything. Thank you

 

[dereckbc]

Re: table 310-15(b)(2)(a)

2-inch conduit is not practical for the application. It is possible to get 100 #12 THHN conductors in a 2-inch conduit, but they could not be used in a 20-amp circuit due to the limitations of 310.15(B)(2)(a). 4 20-amp circuits are all you can get in a conduit using # 12 AWG without going to a larger gauge conductor. Therefore you would use a ?? or ?? conduit for 12 AWG 20-amp circuits.

 

[don_resqcapt19]

Re: table 310-15(b)(2)(a)

The 90?C ampacity for #12 copper is 30 amps. You are permitted to use this ampacity for derating purposes. If you have 9 current carrying conductors, the derating factor from Table 310.15(B)(2)(a) is 70%. This gives you an adjusted ampacity of 21 amps for 9 #12s in a raceway. If you add one more current carrying conductors, then you have a derating factor of 50% and the 10 #12s would be limited to 15 amp overcurrent protection devices. If this is a 3 phase 4 wire system and the neural is not a current carrying conductor, then you can get 9 20 amp circuits using #12s in a common raceway.
Don

 

[porky]

Re: table 310-15(b)(2)(a)

What if diversity is used to find the answer of how many conductors?

 

[dereckbc]

Re: table 310-15(b)(2)(a)

Porky, unless you are a PE and show the calculations with the PE seal you are probable not going to be able to use divesity factor.

Don, you are right about three phase, I was assuming single phase.