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Having a brain spasm, code not close by. We have 9 ccc in a pipe #10 and If I recall correctly we can derate from 40amp. This would put it at .70 X 40=28 amps. Can we still go with the 30 amp breaker because of the next size higher even though the adjustments puts us at 28 amps? Can't recall all the rules for this. Not sure how the inspector would see this install.

The other pipes got at least 12 ccc. So # 8 is being used because I am sure that it jumps to .50 reduction.
 

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Yes #10 is good for 40 amps at 90C so with 70% you would be good at 28 amps. As long as the calculated load is not greater than 28 amps then you can use a 30 amp overcurrent protective device per 240.4(B)

12 current carrying conductor would require 50% reduction so 8 awg at 90C is 55 amps-- brings you to 27.5 at 50%. Next size applies again
 

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In Canada we must use 75 degrees on everything except meter sockets
We must use 75C also but we can use 90C for derating. I believe you can also.

As long as the final overcurrent protective device is not greater than the weakest link- usually 75C you are okay.

If you use nm then you must use the 60 C rating in the NEC
 
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in canada for derating we can use 90C column but must not exceed 75
C column for final ampacity similar to nec
That was my understanding but you will have to help with the code section.
 

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If we take rule 4-006 (1) into consideration we would use 75 degrees and we would only use 90 degrees if we use subrule (2)
 

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Discussion Starter #10
Thanks. co worker says apparently we cannot upsize because they are receptacles. is this true? Can't recall of the top of my head.
 
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