Terminal Limitation

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PowerdT

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San Diego
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Electrical Engineer
I need help to understand the terminal limitations code requirement.

Example of situation:

You have 75C terminal which is panel and the load spec says to use 90C copper, (4) conductor of 6AWG and (1) 10AWG Ground.

Table 310.16 under 90C, 6AWG is 75A

So does that mean I need 4AWG in 75C column?

Thanks for the support!
 
Since the terminal is rated for 75 degrees C the #6 conductor has an ampacity of 65 amps.
 
infinity said:
Since the terminal is rated for 75 degrees C the #6 conductor has an ampacity of 65 amps.
Click to expand...
So what wire size and insulation can be used? 65A is less than 75A required by mfg or I am limited up to 65A so I have to go to 4AWG
 
A panel 100A or less has to use the 60 degree column for final ampacity unless the lugs are rated otherwise. You stated your panel has 75 degree lugs, so I will assume you got that from the panel information. From there, you must use the 75 degree column for final ampacity. This makes sense. The degree rating is the maximum safe operating temperature as determined by the powers that be. Your insulation has a rating, you lugs have a rating. Either or both can have a rating that exceeds the ampacity, but the amps can not exceed the rating of the component. So 90 degree wire can be derated from 90 degrees when it is run with 4 or more current carrying conductors in the conduit, but it can't exceed 75 degree rating at the terminations. It can be derated from 90 degrees when it is run through an area that has a high ambient temperature, but if the terminals are in a location where that higher ambient temperature causes the ampacity to be below that allowed for 75 degrees, then you can't use that table for that purpose. Is that as clear as mud?
 
Strathead said:
A panel 100A or less has to use the 60 degree column for final ampacity unless the lugs are rated otherwise. You stated your panel has 75 degree lugs, so I will assume you got that from the panel information. From there, you must use the 75 degree column for final ampacity. This makes sense. The degree rating is the maximum safe operating temperature as determined by the powers that be. Your insulation has a rating, you lugs have a rating. Either or both can have a rating that exceeds the ampacity, but the amps can not exceed the rating of the component. So 90 degree wire can be derated from 90 degrees when it is run with 4 or more current carrying conductors in the conduit, but it can't exceed 75 degree rating at the terminations. It can be derated from 90 degrees when it is run through an area that has a high ambient temperature, but if the terminals are in a location where that higher ambient temperature causes the ampacity to be below that allowed for 75 degrees, then you can't use that table for that purpose. Is that as clear as mud?
Click to expand...
I think I understand. 4 current carrying Conductor at 6AWG at 90 degree C is 75A. Derate 75*.8= 60A which is below 65A at 75degree C. That result I can use THHN 6AWG
 
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