100 amp sub panel wire size, which column in 310.15 (B) (16) ?

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Stevenfyeager

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electrical contractor
I know if a 100 amp subpanel (not a service that allows #2 AL) requires next size up, #1 AL. But looking at 310.15 (B) (16), in cable form, if I use SER, I use the 60 degree column, only 85 amps. I thought for romex we use the 60 deg column, SER is a cable, correct ? I still sometimes get confused on which column to use.
 
SE cable can be used at the 75° C ampacity, NM cable only at 60° C. #2 aluminum SE cable at 75° C is only rated at 90 amps so you cannot use it for a 100 amp feeder.
 
I am also installing a 125 amp sub panel, 1/0 SER has 120 amps in the 60 degree column. But I dont know if a 120 breaker exists, so I can use the 1/0 AL SER for my 125 amp breaker ? I seem to remember we are allowed to use the next size up breaker if that size does not exist. ?
 
I am also installing a 125 amp sub panel, 1/0 SER has 120 amps in the 60 degree column. But I dont know if a 120 breaker exists, so I can use the 1/0 AL SER for my 125 amp breaker ? I seem to remember we are allowed to use the next size up breaker if that size does not exist. ?
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yes as long as your calculated load doesn't exceed 120 amps
 
You can use #2 alum and install a 90 amp breaker if that is all you need even if the sub panel has 125 amp main breaker
 
Stevenfyeager said:
I am also installing a 125 amp sub panel, 1/0 SER has 120 amps in the 60 degree column. But I dont know if a 120 breaker exists, so I can use the 1/0 AL SER for my 125 amp breaker ? I seem to remember we are allowed to use the next size up breaker if that size does not exist. ?
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I don't believe that this number is correct.
 
1/0 AL @ 75 degrees is 120 amps. 100 amp at 60. But being a large gauge SER you can use 75 degree column. I recall reading something in the 2020 NEC about smaller sizes being limited to the 60 degree column.
 
MattG0311 said:
1/0 AL @ 75 degrees is 120 amps. 100 amp at 60. But being a large gauge SER you can use 75 degree column. I recall reading something in the 2020 NEC about smaller sizes being limited to the 60 degree column.
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Yes #10 and smaller is rated at 60C I believe but who has ever used #10 se cable. Years ago but I doubt it is even used any more.
 
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