100 amp outside disconnect to panel, wire size ?

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Stevenfyeager

Senior Member
Location
United States, Indiana
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electrical contractor
I have an outside disconnect on a pole with a 100 amp back fed breaker. I also have 3 extra breaker spaces I may use outside in that disconnect. May I use #2 AL to feed the inside panel from disconnect ? Is this still considered a 'service' that allows us to use # 2 ? Or is the inside panel a subpanel (not a service) and would require a #1 ? Thanks,
 
LarryFine said:
A feeder need not be larger than the service conductors.
Click to expand...

If the only feed was to that indoor panel it would be considered as using the entire load and can be wired with the #2al. If he added another breaker to the outside panel wouldn't the original indoor panel conductors now become a feeder and need to be #1's ?
 
ritelec said:
If the only feed was to that indoor panel it would be considered as using the entire load and can be wired with the #2al. If he added another breaker to the outside panel wouldn't the original indoor panel conductors now become a feeder and need to be #1's ?
Click to expand...
No, because the feeder need not be larger than the service conductors.
 
?
310.15 (B)(7)
(2) For feeder supplying ENTIRE load 83%

If he adds a breaker to the outside panel, that inside panel's not handling the ENTIRE load anymore.

right?
 
310.15 (B)(7)(3):
In no case shall a feeder for an individual dwelling unit
be required to have an ampacity greater than that specified
in 310.15(B)(7)(1) or (2).

Thus, if #2 al is large enough for the service supplying the entire load, it's large enough for the downstream feeder.
 
I know "what if's" are not taken into account, but this sure seems like a loaded gun for the next guy. With spare spaces at the pole panel, an added breaker would negate the 83% rule.
 
I believe that what Larry is saying is that if the SEC's are the correct size with the 83% rule it doesn't matter where the downstream OCPD's are located when sizing the feeder between the outside pole panel and inside panel.
 
Exactly. #2 is large enough for a 100A service and also large enough for a 100A feeder that serves the entire load of a _dwelling_.

In addition to this, if you have a 100A service that feeds the entire dwelling load, a 100A feeder from this service does not need to be larger than the service conductors, even if it doesn't serve the entire load.

So if you have a 200A service, then #2 is too small for a 100A feeder, but if you have a 100A service than #2 is probably fine.

Jon
 
LarryFine said:
Thus, if #2 al is large enough for the service supplying the entire load, it's large enough for the downstream feeder.
Click to expand...


I think if the first panel has other circuits/feeders that can be taken from it it is the main service panel.

So your saying if from that outside main panel which is fed with the 83% I first took a 30 amp circuit out of it then a 20 amp then I wanted to add a 100 amp panel, I could run #2 using the 83% rule to that new panel ?
 
ritelec said:
So your saying if from that outside main panel which is fed with the 83% I first took a 30 amp circuit out of it then a 20 amp then I wanted to add a 100 amp panel, I could run #2 using the 83% rule to that new panel ?
Click to expand...
Well, indirectly, yes, because the 83% allowance applies to the SECs, and 310.15(B)(7)(3) refers the feeder size to them.
 
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