60-degree column

[DRNDane]

For years i have used only the 60-degree column in table 310-16 to size conductors up to size 1. This method was based on what i read in NEC 110.C-1. This section of the code used to make perfect sense to me, but now, i am confused. This issue came up because i have seen several designs where #3s were being used for 100 amp feeders.

I recognize that i can size based on the 75 and 90-degree columns if i can prove the wire insulation and terminations. So, my question is, am i required to use the 60-degree column to size conductors up to #1?

 

[jbt260]

If the wire and the terminal are rated for 75 deg, then the 75 deg column can be used. Use the 60 deg column if you do not know the terminal temp rating.

 

[raider1]

Welcome to the forum.

So, my question is, am i required to use the 60-degree column to size conductors up to #1?

Not if the terminals and equipment that the conductors are connected to are rated higher.

For example, if I have a 100 amp breaker rated at 75 degrees C and a load center rated at 75 degrees C. If I use #3 copper THHN conductors I am permitted to use the ampacity listed in the 75 degree column.

Chris

 

[BigJohn20]

What about 110.14(c)(1)(3)?

I was taught to refer to Articles 320-340 for what degree rating to use for ampacity, then to refer to the degree rating of the terminals. If both of them matched up, we could use that degree rating. If they didn't match up, we would have to use the lower degree rating.