Protection of feeder that terminates into a breaker

[philly]

How do you handle a case where a feeder circuit is protected by a feeder breaker however the feeder terminates into another breaker?

For instance a 125A breaker is protecting a feeder that terminates into an 100A receptacle breaker. Technically a #1 should be used on this circuit in order to be protected by the 125A breaker. However since the feeder circuit terminates into a 100A breaker can a #2 be used and still protect this feeder by this downstream 100A breaker?

Is this a version of the tap rule or some other rule?

 

[iwire]

Depending on the location and the distance the tap rules might apply.

 

[bsh]

NEC 210.21(B)(1) and 210.21(B)(3)

 

[philly]

Depending on the location and the distance the tap rules might apply.

The distance between breakers is 150ft. The tap rule looks like it allows use within 10ft. Therfore the feeder cable must be protected by the 125A breaker an must be a #1 AWG. The 100A breaker cannot be used for protection of this cable because it is not within 10ft of upstream 125A breaker?

 

[augie47]

There are other tap rules that allow distances beyond 10 ft. You can review Art 240.21 and see which scenario fits your particular application.
Some taps can be unlimited (outside) and some taps may be as long as 100 ft.

 

[LarryFine]

Therfore the feeder cable must be protected by the 125A breaker an must be a #1 AWG.

Another possibility is to replace the 125a breaker with a 100a one.

 

[philly]

There are other tap rules that allow distances beyond 10 ft. You can review Art 240.21 and see which scenario fits your particular application.
Some taps can be unlimited (outside) and some taps may be as long as 100 ft.

This application is completely outdoors except where the circuit origonates in an electrical room. (I'm assuming this is considered outdoors)

That being said it looks like this application falls into the "unlimited" category and the feeder can be sized per the downstream 100A circuit breaker. Is this correct? Is this a good design practice?

Another possibility is to replace the 125a breaker with a 100a one.

Yes this is a possibility. I just want to make sure I completely understand the code with the scenario I proposed above.

 

[augie47]

If I understand your arrangement correctly, it would not satisfy the "outdoor" tap rule. Your conductors ORIGINATE indoors, and the outside tap would allow the reduced ampacity conductors to TERMINATE indoors.
As I see it, even though it might be questionable practice, you could extend the 125 amp conductors to an outdoor location and then run an unlimited "tap" to your 100 amp disconnect.