I am trying to understand the ampacities of 15 and 20 amp ckts in 'romex'. I have had more than one boss tell me that i could not put more than 16 amps on a 20 amp circuit . the logic being 20x .80% derating for continuous duty equals 16 amps.
When i calculate it i use art 334.8 which allows me to derate using the 90 degree column of table; 310.16 unless it end up being higher than the 60 degree column which i must than use it for derating purposes.
table 310.16 puts 12 awg at 25 amps in the 60 degree column .
25 x .80% = 20 amps.
i know that 240.4(d) requires a 20 amp breaker for 12 awg. and as far as i know you do not derate breakers
so is there a step that i am missing to get down to 16 amps or have i had some mistaken bosses, and the allowable ampacity is 20 amps
thanks
When i calculate it i use art 334.8 which allows me to derate using the 90 degree column of table; 310.16 unless it end up being higher than the 60 degree column which i must than use it for derating purposes.
table 310.16 puts 12 awg at 25 amps in the 60 degree column .
25 x .80% = 20 amps.
i know that 240.4(d) requires a 20 amp breaker for 12 awg. and as far as i know you do not derate breakers
so is there a step that i am missing to get down to 16 amps or have i had some mistaken bosses, and the allowable ampacity is 20 amps
thanks