Once again guys!!

[Strahan]

It's late and I'm tired and really starting to get confused. Without much detail I'll keep it simple. When sizing conductors I understand the 60C and 75C columns must be used based on the condition and the 90C column is for correction factors. I have read 110.14 many times and here is the question....
If after proper sizing techniques are used lets say for a load over 100amps using the 75C column it is determined I need a size 1awg now here it is do I have to use an insulation type found in the 75C column or is it ok to pick a THHN found in the 90 Column (sticking with the same size wire determined by the 75 Column). Or am I not allowed to connect a wire rated at 90 to a 75 terminal eventhough proper sizing was used in the 75 column I just choose to use a wire with an insulation rating of 90??? Sorry guys it may be a little confusing

 

[Dennis Alwon]

Basically you must protect your circuit to the weakest link. Using 90C is always fine for your insulation but your terminals are only rated 75C. Thus you can use the 90C to derate but you must protect the wire at it's 75C rating or below.

If the terminals (old panels) were rated 60C then you could still use the 90C insulation but the circuit protection must be at the 60C rating.

 

[Strahan]

Basically you must protect your circuit to the weakest link. Using 90C is always fine for your insulation but your terminals are only rated 75C. Thus you can use the 90C to derate but you must protect the wire at it's 75C rating or below.

If the terminals (old panels) were rated 60C then you could still use the 90C insulation but the circuit protection must be at the 60C rating.

Thank You Dennis excellent explanation!!! Key word protection So I'm ok as long as protect at the 75C rating. This is great now I can sleep better

 

[Dennis Alwon]

You're welcome. I should add that 110.14 causes a lot of confusion. The 75C for 100 amps and 60C for under a 100 amps is only there in case the equipment you use has no termination markings and are not identified for use with 75C rating.

 

[mweaver]

I do believe you have it !!

I do believe you have it !!

Strahan,

When determining conductor ampacity and you find that the 75?C column is necessary for termination temperature ratings, the final ampacity must be derived from this column (or a lesser temperature column). Then, it is permissible to choose conductor insulations from either the 75?C or the 90?C column.


No apologies necessary, because it is actually a little confusing. While all the requirements are there in the NEC, the procedure to determine maximum conductor ampacity within the NEC is not laid out in the most convenient process, go figure…

I do hope this is helpful, (Dennis has provided you the best explaination)

mweaver

 

[Strahan]

Strahan,

When determining conductor ampacity and you find that the 75?C column is necessary for termination temperature ratings, the final ampacity must be derived from this column (or a lesser temperature column). Then, it is permissible to choose conductor insulations from either the 75?C or the 90?C column.


No apologies necessary, because it is actually a little confusing. While all the requirements are there in the NEC, the procedure to determine maximum conductor ampacity within the NEC is not laid out in the most convenient process, go figure?

I do hope this is helpful, (Dennis has provided you the best explaination)

mweaver

Thank you also! This helps tremendously I have found lately that I was getting hung up on this code section and everytime I thought I had it I only formed another question. It is great to be able to ask you guys to help explain. This has been a great help now I can move on with confidence in knowing this section. Thanks Guys!!!!