100 amp subpanel in a house, requires #1 AL, not #2 AL

[Stevenfyeager]

Only one inspector in my part of the state does not allow #2 AL to power up a 100 amp subpanel. He sites the NEC table with dwelling services allowing # 2, but says a subpanel is not a service so I must use 310.16, which calls for # 1. Everywhere else I work, #2 AL is fine with inspectors. He says a service will not use full capacity and a subpanel may. ( same goes for a subpanel to a detached garage, also requires a #1, he says.) Is this unusual?

 

[jumper]

The inspector is correct.

Common install, but a violation none the less.

 

[electrofelon]

Only one inspector in my part of the state does not allow #2 AL to power up a 100 amp subpanel. He sites the NEC table with dwelling services allowing # 2, but says a subpanel is not a service so I must use 310.16, which calls for # 1. Everywhere else I work, #2 AL is fine with inspectors. He says a service will not use full capacity and a subpanel may. ( same goes for a subpanel to a detached garage, also requires a #1, he says.) Is this unusual?

In my experience, very common around here to use #2 at 100 amps for resi, even when it doesnt supply the entire load to a dwelling unit. In fact, I cant recall EVER seeing #2 on a 90 amp breaker, unless I did it!

edit: But to be clear, not correct @100 amps if its not supplying the whole dwelling.

 

[Sierrasparky]

In my experience, very common around here to use #2 at 100 amps for resi, even when it doesnt supply the entire load to a dwelling unit. In fact, I cant recall EVER seeing #2 on a 90 amp breaker, unless I did it!

edit: But to be clear, not correct @100 amps if its not supplying the whole dwelling.

Also the sub feed size does not need to be larger than the service or feeder size ( unless they changed that one too)

 

[kwired]

Also the sub feed size does not need to be larger than the service or feeder size ( unless they changed that one too)

Can you come up with a section that says that?

Kind of doesn't make any sense to require a sub feeder larger conductor then the service/feeder supplying it, but for as long as I can remember the provisions of 310.15(B)(7) (or previous versions of that with different section number) only applied to a feeder/service conductor that supplies the entire load of a dwelling.

If you have a meter main/loadcenter with subfeed lugs by supplying any loads via that loadcenter makes the feeder to another panel within the house no longer serving the entire dwelling and 310.15(B)(7) can no longer apply to the feeder to the sub panel, it is not supplying the entire dwelling load. You don't ordinarily get into trouble with this with a 200 amp service/ subfeeder because 4/0 aluminum can still be protected by a 200 amp device as long as load calculation is less then 180 amps. Run 2/0 copper in that situation tthough and you do have a code violation, might not quite make sense but that is how things are worded AFAIK.

 

[LarryFine]

Kind of doesn't make any sense to require a sub feeder larger conductor then the service/feeder supplying it, but for as long as I can remember the provisions of 310.15(B)(7) (or previous versions of that with different section number) only applied to a feeder/service conductor that supplies the entire load of a dwelling.

As it's written, I agree with you, but I wouldn't hesitate to get the AHJ's opinion on the installation, before installation of course.

If you have a meter main/loadcenter with subfeed lugs by supplying any loads via that loadcenter makes the feeder to another panel within the house no longer serving the entire dwelling and 310.15(B)(7) can no longer apply to the feeder to the sub panel, it is not supplying the entire dwelling load.

To take your example one step further, what if all of the circuitss in said meter/loadcenter were relocated to the new sub-panel?

 

[kwired]

To take your example one step further, what if all of the circuitss in said meter/loadcenter were relocated to the new sub-panel?

That gets tricky, as long as no breakers in the loadcenter then the feeder to the subpanel is feeding the entire dwelling. Add one circuit to it and it isn't, unless that one circuit is a supply to another building or structure - but if that is the case then the feeder conductors are no longer serving just a single dwelling and 310.15(B)(7) can't apply to them.

As I said you don't have so much of a problem with 4/0 aluminum and 200 amp supplies because it is acceptable without (B)(7) anyhow if load calculation isn't over 180, but go with 2/0 copper instead and you can more easily create a situation that isn't code compliant