Derating

[Alwayslearningelec]

So looking to run 1-1/4” EMT with seven 1P 20A circuits that have separate neutrals and one ground. This would be #10 THHN wire fed from 20A breakers and would be feeding receptacles.

That would be 15 wires and would need to derate 50% according to 310.15B and bring the #10 wire good for only 17.5. IS that correct or could I use the 90 degree column when derating?

 

[david luchini]

That's fourteen (14) conductors, and a 50% adjustment factor.

The #10 THHN can be adjusted from the 90C ampacity, so it would be 20A adjusted ampacity.

 

[tank728]

You use the 90 degree column for derating

 

[EC Dan]

Doesn't that require the circuit breaker and receptacle to be rated for 90 degrees C as well?

 

[tank728]

Doesn't that require the circuit breaker and receptacle to be rated for 90 degrees C as well?

No. The circuit will be derated from is 90 degree value, the circuit will be operating at a lower rating. As David showed in an earlier post, they will be running at 20 amps

 

[Alwayslearningelec]

That's fourteen (14) conductors, and a 50% adjustment factor.

The #10 THHN can be adjusted from the 90C ampacity, so it would be 20A adjusted ampacity.

Ahhh right ccc's only. Thanks