derating

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bennny123 said:
How do we know when u have to derate or do temp correction factor.
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Basically when you have more than 3 CCC (current carrying conductors) in the raceway and/or when the ambient temperature of where the conductors are installed is more than 86F.
 
Welcome to the forum. Derating, or "adjustment factors", is covered in 310.15(B)(2)(a) for # of CCC in a raceway, and in the following pages for high (>30*C/86*F) ambient temperatures. There are numerous exceptions, such as sleeves/nipples <24", traveler legs or conductors that cannot be simultaneously energized, etc.
 
derating

JFletcher said:
Welcome to the forum. Derating, or "adjustment factors", is covered in 310.15(B)(2)(a) for # of CCC in a raceway, and in the following pages for high (>30*C/86*F) ambient temperatures. There are numerous exceptions, such as sleeves/nipples <24", traveler legs or conductors that cannot be simultaneously energized, etc.
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So if its only 3 ccc won't need to use adjustment factor do we then just do the math on the number they gave us..
Same thing with a ambient temp ? If doesn't pass 86*F
 
bennny123 said:
So if its only 3 ccc won't need to use adjustment factor do we then just do the math on the number they gave us..
Same thing with a ambient temp ? If doesn't pass 86*F
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Yes, you would do the math based on the full ampacity of the wiring (at 90*C). Keep in mind you're still limited by 240.4(D) on small conductors.

You have to derate (use a smaller breaker) when the adjustment factors limit the wiring to less current than the OCPD is rated for. 9 #12s (all CCC) in a conduit would be .7 x 30A = 21A, still fine for a 20A breaker. 9 #10s (all CCC) tho give .7 x 40 = 28A, so a 30A breaker wont work there.
 
JFletcher said:
Yes, you would do the math based on the full ampacity of the wiring (at 90*C). Keep in mind you're still limited by 240.4(D) on small conductors.

You have to derate (use a smaller breaker) when the adjustment factors limit the wiring to less current than the OCPD is rated for. 9 #12s (all CCC) in a conduit would be .7 x 30A = 21A, still fine for a 20A breaker. 9 #10s (all CCC) tho give .7 x 40 = 28A, so a 30A breaker wont work there.
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Would the next standard size up rule possibly apply?
 
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