Inspector mis-interpreting 705.12(B)(1) and (2) - Feeder taps

[AEStech]

Greetings everyone! I've got an inspector mis-interpreting the feeder tap rules in 705.12, and am looking for some advice on how to (politely) convince him he's incorrect. Unfortunately, everything I send him, he just keeps digging his heels in.

We've performed a completely legal feeder tap: 80A OCPD on the solar, tapped into a 200A feeder, between the 200A main OCPD, and the 200A main breaker panel.

He failed the final, claiming - get this - that 705.12(B)(2) limits a feeder tap to 125% of the feeder ampacity! So according to him, you can never tap more than 50A of solar into a 200A feeder, regardless of whether there's an OCPD on the load side of the tap to protect it.

We all know that 705.12(B)(2) is solely focused on sizing the tap conductors of additional power sources, but he just doesn't get it, and won't listen. Unfortunately, he's the senior inspector in the department.

I may have to take this all the way to the state (as if I have time for that nonsense), so I'm reaching out to ask if anyone has any resources they can share that would help me clarify this to him (other than Mike's Guide of course).

Thanks!

 

[ggunn]

Greetings everyone! I've got an inspector mis-interpreting the feeder tap rules in 705.12, and am looking for some advice on how to (politely) convince him he's incorrect. Unfortunately, everything I send him, he just keeps digging his heels in.

We've performed a completely legal feeder tap: 80A OCPD on the solar, tapped into a 200A feeder, between the 200A main OCPD, and the 200A main breaker panel.

He failed the final, claiming - get this - that 705.12(B)(2) limits a feeder tap to 125% of the feeder ampacity! So according to him, you can never tap more than 50A of solar into a 200A feeder, regardless of whether there's an OCPD on the load side of the tap to protect it.

We all know that 705.12(B)(2) is solely focused on sizing the tap conductors of additional power sources, but he just doesn't get it, and won't listen. Unfortunately, he's the senior inspector in the department.

I may have to take this all the way to the state (as if I have time for that nonsense), so I'm reaching out to ask if anyone has any resources they can share that would help me clarify this to him (other than Mike's Guide of course).

Thanks!

I feel your pain. We ran into a similar situation a few years ago where the inspector's objection would only be valid if current could additively flow both directions at once in the feeder. To make things worse, he managed to get his concern written into the PV interconnection guidelines which were stamped by an AHJ PE (who later admitted to me that he hadn't read it) and codified by the City Council. So, in that jurisdiction we cannot build PV systems with load side taps on feeders unless we replace the entire feeders with conductors that have sufficient ampacity to handle the rated current of the OCPD plus 125% of the inverter current, which we don't do.

 

[wwhitney]

For discussion, the text in question:

2020 NEC 705.12(B)(2) Taps. Where power source output connections are made at feeders, all taps shall be sized based on the sum of 125 percent of all power source(s) output circuit current(s) and the rating of the overcurrent device protecting the feeder conductors for sizing tap conductors using the calculations in 240.21(B).

My only likely not very helpful suggestion would be to focus on that last phrase "for sizing tap conductors using the calculations in 240.21(B)." That limits the scope of the entire sentence. If you aren't "sizing tap conductors using the calculations in 240.21(B)," the sentence imposes no requirements or restrictions. The sentence is in effect an amendment to 240.21(B).

Cheers, Wayne

 

[AEStech]

I feel your pain. We ran into a similar situation a few years ago where the inspector's objection would only be valid if current could additively flow both directions at once in the feeder. To make things worse, he managed to get his concern written into the PV interconnection guidelines which were stamped by an AHJ PE (who later admitted to me that he hadn't read it) and codified by the City Council. So, in that jurisdiction we cannot build PV systems with load side taps on feeders unless we replace the entire feeders with conductors that have sufficient ampacity to handle the rated current of the OCPD plus 125% of the inverter current, which we don't do.

Ugh, that's terrible. I sure hope that it doesn't come to that here, this is our biggest AHJ in the area!

I just don't get it. How do you read:

Use 125% of your inverter output current plus the feeder OCPD rating for sizing tap conductors,

And then interpret that in your head as:

Taps ampacity is limited to 125% of the feeder ampacity, minus the feeder ampacity

It boggles my mind!

 

[AEStech]

For discussion, the text in question:

2020 NEC 705.12(B)(2) Taps. Where power source output connections are made at feeders, all taps shall be sized based on the sum of 125 percent of all power source(s) output circuit current(s) and the rating of the overcurrent device protecting the feeder conductors for sizing tap conductors using the calculations in 240.21(B).

My only likely not very helpful suggestion would be to focus on that last phrase "for sizing tap conductors using the calculations in 240.21(B)." That limits the scope of the entire sentence. If you aren't "sizing tap conductors using the calculations in 240.21(B)," the sentence imposes no requirements or restrictions. The sentence is in effect an amendment to 240.21(B).

Cheers, Wayne

Thanks Wayne. Unfortunately this was the first thing I pointed out to him. I actually think he's just not listening to me because he's sure in his mind that he understands.

 

[wwhitney]

A couple web results from searching "understanding 705.12(B)(2)(2)" (the 2017 numbering, as the 2020 numbering is fairly new):

705.12(B)(2) Taps.

Where inverter output connections are made at feeders, all taps shall be sized based on 125% of the inverters output circuit current + the OCPD rating protecting the feeders as calculated in 240.21(B).

www.electricallicenserenewal.com

Load Side PV Connections

iaeimagazine.org

Not sure how helpful those are. There are some results on ecmweb.com but I don't have an account.

It wouldn't address the inspector's misconception, but in the short run, would running 200A conductors from the splice point to the 80A solar OCPD satisfy the inspector? Then there's no tap . . .

Cheers, Wayne

 

[ggunn]

In the incident we ran into we wanted to land our PV conductors on a 60A breaker in a 100A MLO subpanel at the opposite end of the bus from the lugs. The feeder and subpanel were protected by a 60A breaker in the MDP. The inspector was OK with the subpanel but he said that the feeder had to be able to handle 120A. The inspector got prickly in a meeting we asked for and walked out when we asked him to show us how 120A could flow in that feeder. The incident is known by us as Fight Club.

 

[pv_n00b]

I've always considered these interconnections to a feeder after the main service OCPD to fall under 705.12(B)(1) for feeders and not (2) for taps. Taps off the feeder have to comply with 705.12(B)(2). Otherwise, what is 705.12(B)(1) used for?

 

[wwhitney]

I've always considered these interconnections to a feeder after the main service OCPD to fall under 705.12(B)(1) for feeders and not (2) for taps. Taps off the feeder have to comply with 705.12(B)(2). Otherwise, what is 705.12(B)(1) used for?

In the simplest case, the feeder ends up with three segments:

A) Utility side to splice: this segment has sources of supply at both ends. Assuming the feeder spliced to was not using the tap rules, this segment will be protected on the utility side in accordance with its ampacity. And 125% of the alternate source rating will be less than its ampacity per other rules. So this segment is protected.

B) Splice to downstream loads: this segment has 2 sources of supply at one end. 705.12(B)(1)(a) and (b) address this segment. I think of 705.12(B)(1)(b) as a length unlimited analogue of the tap rules.

C) Splice to alternate source: this segment has sources of supply at both ends. On the utility side it is protected by the feeder OCPD. So if you size this segment smaller than may be protected by the feeder OCPD, it is a tap. And as such has to comply with 705.12(B)(2).

Now if the unspliced feeder was using the tap rules, then things get more interesting. I would think that segment C would have to be sized to match segments A and B. And then A+B and A+C would each need to individually meet the tap rules, as modified by 705.12(B)(2).

One could instead take the approach that feeder segment A is a tap that is terminating at the splice, and as such interconnecting at a feeder that is already a tap would not be allowed. In which case segment A could be upsized to not be a tap, and then the tap rules would just apply to B and C separately.

Cheers, Wayne

 

[AEStech]

A couple web results from searching "understanding 705.12(B)(2)(2)" (the 2017 numbering, as the 2020 numbering is fairly new):

705.12(B)(2) Taps.

Where inverter output connections are made at feeders, all taps shall be sized based on 125% of the inverters output circuit current + the OCPD rating protecting the feeders as calculated in 240.21(B).

www.electricallicenserenewal.com

Load Side PV Connections

iaeimagazine.org

Not sure how helpful those are. There are some results on ecmweb.com but I don't have an account.

It wouldn't address the inspector's misconception, but in the short run, would running 200A conductors from the splice point to the 80A solar OCPD satisfy the inspector? Then there's no tap . . .

Cheers, Wayne

Actually that second one might be helpful if I have to take this to the chief electrical inspector. Those nice simple diagrams could help me prove my point, thank you.

Unfortunately, the inspector in question doesn't have an issue with the tap itself, he thinks we can't feed more than 50A of solar onto a 200A feeder, because 125% of 200A is 250A.

He's not even reading words properly in the code, and is mistaking the inverter output safety factor, for a "feeder safety factor" of some sort. It's doubly frustrating, because we all know that you can't install parallel generation that causes more current to flow on a feeder than it's rated for in any circumstance!

 

[AEStech]

In the incident we ran into we wanted to land our PV conductors on a 60A breaker in a 100A MLO subpanel at the opposite end of the bus from the lugs. The feeder and subpanel were protected by a 60A breaker in the MDP. The inspector was OK with the subpanel but he said that the feeder had to be able to handle 120A. The inspector got prickly in a meeting we asked for and walked out when we asked him to show us how 120A could flow in that feeder. The incident is known by us as Fight Club.

That's pretty funny. Sounds about as reasonable as my guy...

 

[AEStech]

I've always considered these interconnections to a feeder after the main service OCPD to fall under 705.12(B)(1) for feeders and not (2) for taps. Taps off the feeder have to comply with 705.12(B)(2). Otherwise, what is 705.12(B)(1) used for?

You are absolutely correct. My "inspector" has no clue what he's talking about. 705.12 doesn't even address max tap size on a feeder. It simply addresses feeder protection by one of two methods - 705.12(B)(1) a & b, and how to size your tap conductors - 705.12(B)(2).

 

[jaggedben]

Ugh, that's terrible. I sure hope that it doesn't come to that here, this is our biggest AHJ in the area!

I just don't get it. How do you read:

Use 125% of your inverter output current plus the feeder OCPD rating for sizing tap conductors,

And then interpret that in your head as:

Taps ampacity is limited to 125% of the feeder ampacity, minus the feeder ampacity

It boggles my mind!

Going back to the code language:

Where power source output connections are made at feeders, all taps shall be sized based on the sum of 125 percent of all power source(s) output circuit current(s) and the rating of the overcurrent device protecting the feeder conductors for sizing tap conductors using the calculations in 240.21(B).

The language is unclear and illogical on its face. Which variable in the calculations required in 240.21(B) is replaced by "the sum of 125 percent of all power sources and the rating of the overcurrent device protecting the feeder"? Also what is a tap in this case? Could it not be any conductor that is 'not protected at its source' because there's another source that can add to it? If you have no real understanding of how electrical current flows, or if your reading attention span isn't long enough to last for the typical length of a sentence in the NEC - both qualities I've noticed in some inspectors - then it is possible that one of the options is that all conductors fed by both sources are taps which "shall be sized based on the [aforementioned] sum", period.

For the 2017 NEC I submitted a public input with the intention of fixing this. Unfortunately the CMP seems not to have understood the point I was making, or not to have cared enough to add a few more words to the code to clarify the intent. So they left the language ultimately meaningless. And now you are suffering from their failure to write clear code.

IOW, I feel your pain as well. Good luck.

 

[djd]

In the incident we ran into we wanted to land our PV conductors on a 60A breaker in a 100A MLO subpanel at the opposite end of the bus from the lugs. The feeder and subpanel were protected by a 60A breaker in the MDP. The inspector was OK with the subpanel but he said that the feeder had to be able to handle 120A. The inspector got prickly in a meeting we asked for and walked out when we asked him to show us how 120A could flow in that feeder. The incident is known by us as Fight Club.

I have a friend who recently put solar on his house , they used microinverters . The surprise to me was a disconnect before the panel a breaker in the panel and the derating of the main breaker in panel . The derating is what I don`t understand . the bussing just has been reduced in ampacity ? Where is the derating in the 2020 nec . I could not find and don`t see the reason .

 

[ggunn]

I have a friend who recently put solar on his house , they used microinverters . The surprise to me was a disconnect before the panel a breaker in the panel and the derating of the main breaker in panel . The derating is what I don`t understand . the bussing just has been reduced in ampacity ? Where is the derating in the 2020 nec . I could not find and don`t see the reason .

705.12(B)(3)(2), aka "The 120% Rule". When a PV system is interconnected in an MDP through a breaker at the opposite end of the busbar from the main breaker, the main breaker and the PV interconnection breaker ratings must sum to 120% or less of the rating of the busbar. Most residences' main breakers are significantly oversized for the actual load, so solar companies often will replace the main breaker with a smaller one to comply with the code.

BTW, if the PV interconnection is not at the opposite end of the busbar it must comply with 705.12(B)(3)(1), which drops the allowed breaker sum from 120% to 100%.

The disconnect before the interconnection breaker is a utility requirement, not one of code, and the usual reason is so that if they feel the need the utility can come in and lock the PV AC disco in the OFF position.

 

[djd]

Thank you for your response it does make more sense the solar creating current , not just a little miss on my part .