NEC Article 110.14

[gfarra]

The classical conductor selection based on the terminal equipment temperature rating:

If a 90 deg C rated insulated conductor is terminated at a 75 deg C equipment in a 30 dec C ambient and this same conductor is routed through a 40 deg C ambient location, can this conductor size be selected based on the 90 deg C amapacity without exceeding the 75 deg C temperature in the 30 deg C ambient location?

 

[bphgravity]

Re: NEC Article 110.14

You are permitted to correct the ampacity of the conductors based on the 90? rating, however that value can not exceed the 75? rating of that same conductor.

 

[gfarra]

Re: NEC Article 110.14

Here is my thinking:

The terminations and conductor ampacity are two entirely separate issues. The use of the 75 oC column of the NEC tables for the terminations doesn't mean the selection shall start in that column to determine the overall conductor ampacity. I believe the selection shall first start by using the 90 oC temperature limits and its resulting ampacity while considering applicable de-rating factors. Then this same conductor size shall not exceed the lower temperature equipment rating of 75 oC whilst ambient temperature effect is considered

 

[charlie b]

Re: NEC Article 110.14

For example, take a #8 THHN. Its 90C rating is 55 amps. The derating factor at 40C ambient is 91%. Multiply 55 times 0.91 and you get 53.35 amps. That is higher than the 75C rating of 50 amps. So the ampacity of this conductor, in this installation, is 50 amps.

 

[gfarra]

Re: NEC Article 110.14

I feel as though I am not expressing my point across well:

What if the ambient temperature is 40 deg C throughtout the cable route and only 30 deg C where the cable terminate?

I want to first derate for the higher ambient using the 90 dec C column, then verify that this same conductor will not exceed the 75 deg C of the equipment located in a lower ambient, i.e. 30 deg C.

Does the code disallow this approach?

 

[rbalex]

Re: NEC Article 110.14

The NEC permits that approach; in fact, that is essentially what Charlie B did.

 

[pierre]

Re: NEC Article 110.14

110.14
(C) Temperature Limitations. The temperature rating associated with the ampacity of a conductor shall be selected and coordinated so as not to exceed the lowest temperature
rating of any connected termination, conductor, or device. Conductors with temperature ratings higher than specified for terminations shall be permitted to be used for ampacity adjustment, correction, or both.

 

[gfarra]

Re: NEC Article 110.14

Thanks to all for your replies.

Gus Farra
Fluor Power, Greenville.