Wire ampacity, feeder tap(s)

[ggunn]

I am helping a client with something that is a bit out of my wheelhouse, so I'd like a little help. He will be using a 400A ATS routed to a gutter where he will have connections via Polaris blocks to a 100A panel and a 400A fused disco fused at 300A. I believe this is legal because I have seen service entrances wired this way, but in this case the supply is from a 400A feeder instead of service conductors.

Clearly this is a feeder tap situation, but I am not sure how to size the conductors between the tap and the destination OCPDs. I thnk that the equipment will be grouped, so I think we can assume that 240.21(B)(1) is applicable, but from the point where the conductors split, which is the feeder and which is the tap, or are they both taps?

 

[don_resqcapt19]

Any conductor that has a supply side OCPD with a rating greater than the ampacity of the conductor is a tap. Not sure from your description exactly what you have for conductor sizes.

 

[augie47]

What are the rating of the service disconnect and generator OCP devices ahead of the ATS ??

 

[ggunn]

Any conductor that has a supply side OCPD with a rating greater than the ampacity of the conductor is a tap. Not sure from your description exactly what you have for conductor sizes.

Conductor sizing is what I am working on. From the ATS to the tap the conductors will be sized for 400A; the question is what size the conductors need to be from the Polaris blocks to the 100A and 300A OCPD, hence the question of if they are both taps and should be sized per 240.21(B)(1). It sounds like you are answering in the affirmative; is that correct?

 

[wwhitney]

Conductor sizing is what I am working on. From the ATS to the tap the conductors will be sized for 400A;

And presumably the ATS or upstream of it has 400A OCPD.

the question is what size the conductors need to be from the Polaris blocks to the 100A and 300A OCPD,

Either (a) 400A (they are not taps) with no limit , or (b) less (they are taps), subject to the limits of the options available under 240.21(B).

Cheers, Wayne

 

[electrofelon]

Conductor sizing is what I am working on. From the ATS to the tap the conductors will be sized for 400A; the question is what size the conductors need to be from the Polaris blocks to the 100A and 300A OCPD, hence the question of if they are both taps and should be sized per 240.21(B)(1). It sounds like you are answering in the affirmative; is that correct?

The conductor size from the tap point to the OCPD would be whatever complies with the tap rule you are using. The 100A is main breaker correct?

 

[don_resqcapt19]

Conductor sizing is what I am working on. From the ATS to the tap the conductors will be sized for 400A; the question is what size the conductors need to be from the Polaris blocks to the 100A and 300A OCPD, hence the question of if they are both taps and should be sized per 240.21(B)(1). It sounds like you are answering in the affirmative; is that correct?

Yes, they are both taps. If the taps are 10' or less of wire length, they would just need to have an ampacity at least equal to the rating of the load end OCPD. The round up rule in 240.4(B) cannot be used here. If the length exceeds 10' but not 25', the tap to the 100 amp OCPD would have to have an ampacity of at least 133 amps.

 

[ggunn]

Either (a) 400A (they are not taps) with no limit , or (b) less (they are taps), subject to the limits of the options available under 240.21(B).

Um, yes, I get that. Whether they are both taps or not is the seminal question.

 

[wwhitney]

Um, yes, I get that. Whether they are taps are not is the seminal question.

Yes, the answer depends on the size of the conductors.

Don gave you the answer in post 2: if the OCPD at the ATS is 400A, then any conductor segment between that 400A OCPD and the next downstream OCPD that has an ampacity less than 351A (per 240.4(B)) is a feeder tap.

Cheers, Wayne

 

[electrofelon]

Um, yes, I get that. Whether they are both taps or not is the seminal question.

The wording in the feeder tap rules could be a little clearer, but basically you don't have to continue the feeder after you tap it - the feeder can end and they will both be feeder taps. In fact you don't even need a feeder at all, and the taps can start right at the OCPD.

 

[ggunn]

The wording in the feeder tap rules could be a little clearer, but basically you don't have to continue the feeder after you tap it - the feeder can end and they will both be feeder taps. In fact you don't even need a feeder at all, and the taps can start right at the OCPD.

That's what I figured; thanks.