subpanel wire sizing question

[Stevenfyeager]

We've agreed that a 100 subpanel in a house requires #1 AL and not #2 like all electricians around here have been running for decades. (Although there is only one inspector in this area that requires larger than #2, because he says a subpanel is not a service) (and the older NEC books which they still use has the dwelling services sizing table instead of 2017 book, 83 %). Does that include wire from an outside disconnect? Is that considered a service or a branch circuit?
Which makes me ask, when we run 4/0 AL from an outside disconnect to a 200 amp house panel, is that sufficient? Table 31.15b says 4/0 AL only carries 180 amps. Thank you.

 

[augie47]

Two things in your favor.
Looking at 4/0AL in general and accepting the 180 amp rating, 240.4 will allow you to protect it at 200 amps (next size up) provided the load does not exceed the 180 amp rating.
Secondly, 310.15(B)(7) allows "whole house feeders", such as one that connects the interior panel with an outside disconnect, to be covered by the 83% rule which for a 200 amp service would be 166 amps, well below the 180 amp rating of the SE,.

 

[Stevenfyeager]

Two things in your favor.
Looking at 4/0AL in general and accepting the 180 amp rating, 240.4 will allow you to protect it at 200 amps (next size up) provided the load does not exceed the 180 amp rating.
Secondly, 310.15(B)(7) allows "whole house feeders", such as one that connects the interior panel with an outside disconnect, to be covered by the 83% rule which for a 200 amp service would be 166 amps, well below the 180 amp rating of the SE,.

Thank you.

 

[Dennis Alwon]

As long as the feeder carries 100% of the load to the sub panel then you can use the table.

 

[sw_ross]

60* Column ampacity requirement

60* Column ampacity requirement

Isn't the reason for requiring the use of #1 Al SER cable as a feeder to a 100amp sub-panel because of the requirement to use the 60* column for ampacity? Especially when it's embedded in thermal insulation?

I guess if it's not embedded in thermal insulation you could use 75* ampacity?
Nothing to do with the 83% rule...

 

[infinity]

Isn't the reason for requiring the use of #1 Al SER cable as a feeder to a 100amp sub-panel because of the requirement to use the 60* column for ampacity? Especially when it's embedded in thermal insulation?

I guess if it's not embedded in thermal insulation you could use 75* ampacity?
Nothing to do with the 83% rule...

If applying the 83% rule the #1 Al has an ampacity of 85 amps @ 60° C so you're good. (100 amps*83%=83 amps). If you're feeding a 100 amp sub-panel that is not carrying the entire load then you need either #1 @75° C or #1/0 @ 60° C depending on the thermal insulation variable.