Ampacity Adjustment, Correction and Terminals

[Devin Hanes]

Would anyone mind trying to explain this language in 310.15(B) to me? Specifically the part in bold below. Is it just trying to say the same thing as 110.14(C)? The way it is actually written would mean if your adjusted and corrected ampacity is still above your 75c ampacity then you can't use the 90c rating for adjustment and correction, which isn't what I believe they are trying to say. Also, wouldn't it make since to not have the language in this section since this is covered in 110.14(C) and in my opinion more clearly.

Thanks

310.15(B) (2017)

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).

110.14(C)

Conductors with temperature ratings higher than specified for terminations shall be permitted to be used for ampacity adjustment, correction, or both.

 

[don_resqcapt19]

It simply means that where the adjusted and corrected ampacity exceeds the 75°C ampacity, you are limited to the 75°C value.

 

[Carultch]

"Temperature correction" and "ampacity adjustment" factors used to be collectively called derate factors. I will call them derate factors in this post for simplicity.

What this is saying:
Calculation #1: forget about derate factors. Determine the termination temperature rating, which is most commonly 75C. Look in the 75C column for the ampacity you need, in order to be sufficient for the load, and sufficient to be protected by the OCPD.

Calculation #2: Now apply derate factors. Look at the wire's temperature rating. Find the ampacity that corresponds to it, and multiply by the product of both derate factors. Is it still sufficient for the load and sufficient to be protected by the OCPD? If yes, then you are good to keep the size. If no, then increase the size until it is.

This is the primary value to having 90C wire when you have to use 75C terminals, is that it gives you some headroom above what you need for terminations alone, in order to apply your derate factor calculations. Most equipment in practice has 75C terminations.

 

[Devin Hanes]

Thanks,
That's what I have thought it meant and the the intention behind it, but do you believe the way it is actually written says that? And that it needs to be covered here since this is already covered in 110.14(C)?

 

[synchro]

It simply means that where the adjusted and corrected ampacity exceeds the 75°C ampacity, you are limited to the 75°C value.

Thanks,
That's what I have thought it meant and the the intention behind it, but do you believe the way it is actually written says that? And that it needs to be covered here since this is already covered in 110.14(C)?

The way it's written accurately describes how the corrected and adjusted ampacity can be applied using the conductor's temperature rating when the resulting ampacity value doesn't exceed the conductor ampacity at the temperature rating of the terminations (e.g. 75°C).
It's unwritten but I think implied that when this calculated value is higher than the conductor ampacity at the termination's temp rating such as 75°C, then you use the 75°C ampacity as Don mentioned.
In this situation you still can utilize the 90°C rating to your advantage because it avoids the derating that could be required if 75°C conductors were used.