Derating

[mstrlucky74]

If running lighting circuits from panel and you have a (6) 20a circuits with separate neutrals then you have 12 current carrying conductors and must derate by 50%. #10’s are good for 35A at 75 degree but if running all 6 circuits in one pipe from 20A breakers you could not use #10’s as they would only be good for ~17A, correct?

 

[charlie b]

If you use a conductor that has 90C insulation, such as THHN, you can start with the 90C column for derating purposes. The 90C ampacity of a #10 is 40 amps. Derate that by 50% and you are able to use this with a 20 amp breaker. Reference 110.14(C).

 

[mstrlucky74]

If you use a conductor that has 90C insulation, such as THHN, you can start with the 90C column for derating purposes. The 90C ampacity of a #10 is 40 amps. Derate that by 50% and you are able to use this with a 20 amp breaker. Reference 110.14(C).

Oh right I did forget about using 90 degree column for derating. TY!!

 

[infinity]

With #10 AWG 90° C conductors you can get up to 20 CCC's before the derating drops you below 20 amps. For lighting circuits it's a little more complicated because you can exceed 20 CCC's and possibly use the next size up rule and still use 20 amp OCPD's.