load-side tap headache

[wwhitney]

Distribution equipment is not defined but I understand it to mean all equipment other than the loads themselves.

I'm inclined to agree, that was my how I understood it on first reading, although I'm not super-confident in my understanding.

As to phrase "where this distribution equipment is capable of supplying multiple branch circuits or feeders or both," I read "supplying" there to mean via direct connection, as opposed to eventually supplying downstream. Because with the latter meaning of supplying, every feeder supplies a branch circuit, so any discussion of feeders versus branch circuits is redundant. The phrase could just read "where this distribution equipment is capable of supplying multiple branch circuits".

So since the writers put in the "or feeders or both" they are indicating that supplying just means by direct connection. As such, none of 705.12(D)(1) through (7) apply to the feeders themselves, they apply only to panelboards, some tap boxes, some connectors, etc. At least, that's my take.

I'd be very interested to hear from the practicing PV designers here whether any of them has ever tried this line of reasoning for the 2011 NEC on an AHJ official.

Cheers, Wayne

 

[jaggedben]

So I think we've found a solution. Going to add a new 200A sub panel , replace the 100A main in the meter panel with a 175A sub feed (allowing 65A of PV in the new sub) and relocate the 100A that was in the meter main to the sub which will in turn feed the remote existing 200A sub. Clear as mud?

This should all comply with the 120% rule unless I am missing something.

Smart$ has already covered some of this territory, but you get to keep the 100A breaker at the main. Your PV breaker is 60A. So under 2011 your ampacity calculation for your new subpanel is (100+60)/1.2 which is 133A. Your 200A rated subpanel is therefore appropriate because 125A is not enough and hardly anyone manufacturers something in between. Your AHJ may or may not apply the same calculation to the feeder from main to sub - a lot of them won't - but let's assume they will because it's the same basis for rejecting your load side tap. Your feeder thus needs to be 1/0 going by the 75C terminal rating.

Once you're done with this project forget all the lessons because on Jan 1st it all changes. Under the 2016 California Electric Code you should be able to do your load side tap as long as you install a 100A main breaker in the down stream subpanel. You could try suggesting this to your AHJ now, but I think maybe it will be easier to save it for the next project.

 

[deadshort]

Smart$ has already covered some of this territory, but you get to keep the 100A breaker at the main. Your PV breaker is 60A. So under 2011 your ampacity calculation for your new subpanel is (100+60)/1.2 which is 133A. Your 200A rated subpanel is therefore appropriate because 125A is not enough and hardly anyone manufacturers something in between. Your AHJ may or may not apply the same calculation to the feeder from main to sub - a lot of them won't - but let's assume they will because it's the same basis for rejecting your load side tap. Your feeder thus needs to be 1/0 going by the 75C terminal rating.

Once you're done with this project forget all the lessons because on Jan 1st it all changes. Under the 2016 California Electric Code you should be able to do your load side tap as long as you install a 100A main breaker in the down stream subpanel. You could try suggesting this to your AHJ now, but I think maybe it will be easier to save it for the next project.

Okay, 1/0 it is. Thanks.

Yeah, I already explained to the AHJ that there is a 100A main protecting all the loads in the sub but he wasn't having it. He's just one of those guys that reads the code verbatim and that is where the buck stops. No room for discussion. Hair pulling, screaming internally frustrating but, so it goes.

Bring on the 2016 code adoptions!

Cheers!

 

[Smart $]

...
So since the writers put in the "or feeders or both" they are indicating that supplying just means by direct connection. As such, none of 705.12(D)(1) through (7) apply to the feeders themselves, they apply only to panelboards, some tap boxes, some connectors, etc. At least, that's my take.
...

If 705.12(D)(1) through (7) does not apply to feeders themselves, then why does 705.12(D)(2) apply to bus or conductor?

 

[ggunn]

Okay, 1/0 it is. Thanks.

Yeah, I already explained to the AHJ that there is a 100A main protecting all the loads in the sub but he wasn't having it. He's just one of those guys that reads the code verbatim and that is where the buck stops. No room for discussion. Hair pulling, screaming internally frustrating but, so it goes.

Give the guy a break; he's just trying to do his job. If he were to approve a project that he knows violates the NEC as he understands it, he could lose his position.

 

[wwhitney]

If 705.12(D)(1) through (7) does not apply to feeders themselves, then why does 705.12(D)(2) apply to bus or conductor?

To cover the case of a tap box or a feeder conductor with multiple taps, which would allow a single conductor to supply "multiple feeders or branch circuits or both".

I'm not really sure what I think of all this, part of me wants to say the 2011 language will soon be obsolete, so we can leave it as undecided. At least 705.12(D)(2) improved in the 2014 and (hopefully) 2017 NECs.

Cheers, Wayne

 

[Smart $]

.... At least 705.12(D)(2) improved in the 2014 ...

Yeah... it actually says feeders.

 

[wwhitney]

OK, now that the OP has found a good solution to their issue, I have a question about the original one line diagram from the first post.

If I'm reading it correctly (it's rather small), there are #4 copper conductors running from the 60A PV output breaker to the point of connection in the middle of the existing #2 copper SER 100A feeder.

From the utility side of things, that #4 feeder is being protected at 100A, while its 75C ampacity is 85A, and 90A is the next standard OCPD size. So does the #4 feeder have to comply with the feeder tap rules? Or is there some language in 690 or 705 that allows this?

Thanks,
Wayne

 

[jaggedben]

OK, now that the OP has found a good solution to their issue, I have a question about the original one line diagram from the first post.

If I'm reading it correctly (it's rather small), there are #4 copper conductors running from the 60A PV output breaker to the point of connection in the middle of the existing #2 copper SER 100A feeder.

From the utility side of things, that #4 feeder is being protected at 100A, while its 75C ampacity is 85A, and 90A is the next standard OCPD size. So does the #4 feeder have to comply with the feeder tap rules? Or is there some language in 690 or 705 that allows this?

Thanks,
Wayne

Tap rules. 2011 code is totally vague on it, but there's nothing in 705 (or 690) that modifies the tap rules.

2014 has the utterly horribly worded 705.12(D)(2)(2). I tried to get it fixed in 2017 but I don't think they understood my point about the grammar. I believe it's supposed to be that you add the feeder OCPD and 125% of the inverter output, and use that number as an assumed OCPD protecting the feeder for the purposes of 240.21(B) calculations. At any rate they are still invoking the tap rules.

Another thing, speaking to your question, is that Table 310.15(B)(7) allows #4 for 100A feeders if they serve the whole house load. One can play some semantic games with that language when solar gets tied in, but the point is that an existing #4 CU feeder would be compliant and it hardly makes sense for the tap to be sized larger.

 

[pv_n00b]

If anyone is interested the reason conductors were included in distribution equipment in 2011 and before is that people were concerned that someone would come along later and tap the conductor, making it a point of "distribution" that was then fed from both ends and therefore needed to comply with the 120% rule. As was sometimes the case, planning for someone to come in later and do something stupid would limit how equipment could be installed.

It took years of making the case over and over again but in 2014 the CMP finally accepted that conductors were not the same as bus bars in a panel.