Derating conductors

[lvdugger]

When derating conductors in a race way for the number of conductors and for temperature do you start the derating from the 90 degree C chart on 310.15B or do you use the termination lug temperature limitations on 110.14 C ! for your starting point for the derating of the conductors. Thanks

 

[tom baker]

Ampacity adjustment (what the NEC calls it) starts with the 90 deg conductor ampacity
Nearly all terminals are rated 75 deg C, often a mfg uses a lug that is labeled 90 deg C but used at 75 deg c

 

[ZacharyBob]

110.14 will have you derating TO the ampacity listed in the 60 degree column for circuits rated 100A or less or marked for AWG #14-#1,
and derated TO the 75 degree column for circuits over 100A or larger than AWG #1.

The column you derate FROM (starting point) will be based on the insulation type of your conductor.

310.15 (A) reads;
"..The temperature correction and adjustment factors shall be permitted to be applied to the ampacity for the temperature rating of the conductor, if the corrected and adjusted ampacity does not exceed the ampacity for the temperature rating of the termination in accordance with the provisions of 110.14(C)."

 

[roger]

Zach, please update your profile to show a better location, at least the state you are in, it helps others when replying.

 

[winnie]

When derating conductors in a race way for the number of conductors and for temperature do you start the derating from the 90 degree C chart on 310.15B or do you use the termination lug temperature limitations on 110.14 C ! for your starting point for the derating of the conductors. Thanks

When adjusting ampacity _in the raceway_ you start with the temperature rating of the conductor. Most are 90C rated and you can use that, but sometimes (especially if reusing previously installed conductors in wet locations) you might be dealing with 75C conductors. In a raceway you need to consider the total number of conductors as well as ambient temperature.

When adjusting ampacity at the termination, where you only have to consider ambient temperature, you would start with the lower of the conductor or termination temperature rating. This is very rare, but I suppose it would happen if say you had a termination in a high temperature environment.

-Jon

 

[roger]

Thank you Zach.