83 % rule apply with feeder taps?

[electrofelon]

Only that that would be weird and I've never seen such a thing. Pardon my lack of imagination.
Regardless, whatever unusual scenario you come up with, 240.21 just overrides 310.12.

How do we know 240.21 overrides 310.12? I don't even see it as overriding really, 310.12 just changes the ampacity in some situations.

Edit: I just reread Don's post number 21, honestly I'm not really seeing it. So his theory is if it said the "ampacity shall be" vs " Shall be permitted to have an ampacity....."? I don't really see a distinction and it seems to me in either case it's telling you what the ampacity is.

 

[Sparky38]

How do we know 240.21 overrides 310.12? I don't even see it as overriding really, 310.12 just changes the ampacity in some situations.

Edit: I just reread Don's post number 21, honestly I'm not really seeing it. So his theory is if it said the "ampacity shall be" vs " Shall be permitted to have an ampacity....."? I don't really see a distinction and it seems to me in either case it's telling you what the ampacity is.

Electrofelon, You would allow the 83% rule for feeders that are tapped off a 400 amp breaker (read post #1) before replying, How would you have the contractor come into compliance.

 

[electrofelon]

Electrofelon, You would allow the 83% rule for feeders that are tapped off a 400 amp breaker (read post #1) before replying, How would you have the contractor come into compliance.

I actually am not dead set on the 83% rule applying to feeder taps, just exploring the language and others opinions, it's an interesting idea. Regardless of that, as has been pointed out there are other issues like the conductors not being in a raceway and in this situation the 83% rule wouldn't apply anyway because each set of conductors is not carrying 100% of the load. I don't see any easy way to make this code compliant. You're probably going to need to add 200 amp ocpds at the start of the ser.

 

[wwhitney]

How do we know 240.21 overrides 310.12?

It's more that 240.21 requires OCPD at the source of supply, unless you meet one of the tap rules. If you choose to take advantage of 310.12, then as a side effect you won't meet the tap rules, so you must put the OCPD at the source of supply as usual.

Which is another way to fix the installation mentioned in the OP--put 200A OCPD outside by the 400A OCPD, with full 200A ampacity conductors between the 400A OCPD and the new 200A OCPD.

Cheers, Wayne

 

[Sparky38]

It's more that 240.21 requires OCPD at the source of supply, unless you meet one of the tap rules. If you choose to take advantage of 310.12, then as a side effect you won't meet the tap rules, so you must put the OCPD at the source of supply as usual.

Which is another way to fix the installation mentioned in the OP--put 200A OCPD outside by the 400A OCPD, with full 200A ampacity conductors between the 400A OCPD and the new 200A OCPD.

Cheers, Wayne

Thanks for your responses, It sounds like we’re basically on the same page. I mentioned a few of these options to the contractor. And then shortly after he flew off the handle on me and called the Cheif who signed off on it. Just making sure that I haven’t lost my mind or anything. Thanks for everyone’s help I really appreciate it! Enjoy your weekend

 

[kwired]

I'm struggling to think of a possible way that a tap would ever qualify for the 83% rule in the first place. If it's protected by the service disconnect OCPD it's not a tap. If it's small enough to be a tap then it doesn't qaulify for the 83% rule for one or more reasons. So it's a moot question.

I disagree with the "small enough" part. In multifamily applications you could have taps supplying individual dwelling units. If it supplies the entire load of a dwelling unit it is eligible to consider the 83% rule. There could be other reasons it ends up being disqualified though.