derating OP

[AAEB]

should the OP follows after derating the current carrying conductors? I have a scenario here where i use a bunch of 20A CB"s for landscape lightings. We pulled 20-#12AwG THHN-THWN-2, 90deg. via 1-1/4" RNC going to the lighting panelboard. Since art. 310.15(B)(2)(a) requires 50% derating and the ampacity of no.12 is 30A, do i need to change the OP to 15A? or upsize cable to No.10 which has an ampacity of 40A? or am i interpreting it incorrectly?

thanks guys!...

 

[macmikeman]

Since art. 310.15(B)(2)(a) requires 50% derating and the ampacity of no.12 is 30A, do i need to change the OP to 15A? or upsize cable to No.10 which has an ampacity of 40A? or am i interpreting it incorrectly?

thanks guys!...

Either way is ok.

 

[AAEB]

does the circuit load affects the derating? for example, majority of the circuits only loaded by 2amps maximum, 10% loaded. do i still need to apply derating?

 

[iwire]

does the circuit load affects the derating?

No

for example, majority of the circuits only loaded by 2amps maximum, 10% loaded. do i still need to apply derating?

Yes

 

[charlie b]

for example, majority of the circuits only loaded by 2amps maximum, 10% loaded.

In that case, using a 15 amp breaker will not cause any problems with the operation of the system. Much cheaper solution, and changing to #10 wire would be a complete waste. But you have to do one or the other, as the others have already said.