Derated Ampacity / Next Size Up

[ohmti787]

If the ampacity of a wire after applying derating factors dropped down to more than 50%, I should still be able to use the next size up OCPD to protect that circuit, correct?

Eg: string of micros putting out 15A and wire ampacity dropped to 16A after derate. Can I still use a 20A breaker for that string?

Thanks y'all

.....and Happy New Year!!

 

[Dennis Alwon]

If the ampacity of a wire after applying derating factors dropped down to more than 50%, I should still be able to use the next size up OCPD to protect that circuit, correct?

Eg: string of micros putting out 15A and wire ampacity dropped to 16A after derate. Can I still use a 20A breaker for that string?

Thanks y'all

.....and Happy New Year!!

I don't see any reason why you couldn't.

 

[don_resqcapt19]

Per the Article 100, the ampacity of a conductor is based on the conditions of use. So when you apply ampacity adjustment and/or ampacity correction factors, that becomes the ampacity, and you use that adjusted and/or corrected ampacity just like you would use the table ampacity for applications where adjustment and/or correction was not necessary.

 

[jaggedben]

Not only are you allowed to use a 20A breaker, you're actually required to by 705.30(B). (2020 NEC reference.)

Note: 705.28(B) requires you to use 20A rated wire before adjustment and correction. But I think we can safely assume that you're doing that.

 

[ohmti787]

Not only are you allowed to use a 20A breaker, you're actually required to by 705.30(B). (2020 NEC reference.)

Note: 705.28(B) requires you to use 20A rated wire before adjustment and correction. But I think we can safely assume that you're doing that.

We are. It's just the whole reduced ampacity to 50% less that kinda threw me off.

Thanks for the insight!