NEC 2020 705.12(B)(3)(5)

[pendexter]

First time posting here, this forum has been a great help as I develop my understanding of NEC codes. I've tried searching but haven't been able to find anything relevant.

California recently went on the 2020 NEC code cycle, and I noticed 705.12(B)(3)(5) which I have not been able to find any discussions on. (1) - (4) are the same backfeed rules as the 2017 cycle, I saw a great writeup by Mayfield on (6), but to me (5) is the interesting one.

"Connections shall be permitted on switchgear, switch-boards, and panelboards in configurations other than those permitted in 705.12(B)(3)(1) through (B)(3)(4) where designed under engineering supervision that includes available fault-current and busbar load calculations."

I'm reading that as long as an electrical engineer stamps off on the panel, we can exceed the 120% rule if we have a load calc and the available fault current. Is that correct? If so, this seems like the fabled "150% rule" that has been discussed for a few years. I can see why the rules comittee would rather have an EE sign off rather than a blanket 150% rule.

Has anyone used 705.12(B)(3)(5) to exceed 120% on a project? If so, where there any challenges to getting the project approved? Is getting the "available fault current" a hassle?

Getting main panel upgrades done in California has been challenging in recent years with the updated utility requirements resulting in relocations, feeder line upgrades, wait times in the months to move things forward, high cost of the electrical work, etc. It would be wonderful to have another code in my backpocket for more troublesome projects.

If I'm completely misinterpreting the code, I'd greatly appreciate any corrections.

 

[ggunn]

I'm pretty sure that's what it means, but if you can get a PE to seal it he is putting his license on the line, and even then the AHJ can reject it.

 

[wwhitney]

I'm pretty sure that's what it means, but if you can get a PE to seal it he is putting his license on the line, and even then the AHJ can reject it.

How can the AHJ reject it? 705.12(B)(3)(5) says it "shall be permitted".

Cheers, Wayne

 

[pv_n00b]

Has anyone used 705.12(B)(3)(5) to exceed 120% on a project? If so, where there any challenges to getting the project approved? Is getting the "available fault current" a hassle?

We do mostly large C&I PV systems and we do this all the time. We did it under the 2017 NEC too since no guidance was provided for SWBD interconnections. We see no AHJ pushback once they know it has been done under engineering supervision. Maybe there are AHJs out there that would not like it but we have not found them yet.

 

[pv_n00b]

Is getting the "available fault current" a hassle?

It's a middle of the road hassle. We have a letter we send to the utility to get the utility fault contribution and they are generally forthcoming. We do a lot of power studies so we need the available fault current, source impedance, utility transformer spec, future maximum fault current, etc. This information is often in the system impact report the utility generates for larger interconnections.

 

[pendexter]

Thanks for all of the replies. I'm reaching to our electrical PE to see what his thoughts are, what ratio he's ok with, etc. I'm fully expecting some pushback for the first few submissions, but it'll still be faster going back and forth with the jurisdiction than waiting for an MPU.

I recall reading a few years back that there were discussions on possibly increasing the 120% rule and that the 120% was a safe value for both new and old panels. I'd imagine that a brand new 200/200 panel could handle a bit more of a change in temperature than a 30 year old Zinsco, for example.

Hopefully it's only a middle of the road hassle getting the utility fault contribution for residential projects from the big 3 utilities. New year, new opportunities...

 

[pv_n00b]

I would not try to apply (5) to anything smaller than a SWBD, maybe a large power panelboard. I would not apply it to a small residential panelboard.

 

[ggunn]

How can the AHJ reject it? 705.12(B)(3)(5) says it "shall be permitted".

Cheers, Wayne

An AHJ has the ability to amend/enforce the NEC in any way they see fit. We run into code legal things that an AHJ will not accept quite frequently.

 

[pendexter]

I would not try to apply (5) to anything smaller than a SWBD, maybe a large power panelboard. I would not apply it to a small residential panelboard.

This brings up an interesting question. My understanding is that in the NEC there is no distinction between a panel board and a residential main panel (load center). However, I'm wondering if the phrase "switchgear, switch-boards, and panelboards" was purposefully used to imply larger services.

What is your reasoning behind recommending more than 120% on larger panels but not smaller residential panels, if you don't mind me asking?

 

[CGleed]

We are trying to apply this code section, with the PV breaker at the end of the busbar in one gear section that has the bussing between sections connecting in the center of the busbar at all distribution sections. We have an EE stamped approval and the AHJ is not very receptive toward the idea, but is not completely unwilling to entertain it.

@pv_n00b - can you share what AHJ has accepted the application of 705.12(B)(3)(5)?

We are under NEC 2017 for our project (permitted before 1/1/23 when the AHJ adopted 2020 code), but rely on 705.12(B)(3)(e) in the same manner.

 

[electrofelon]

An AHJ has the ability to amend/enforce the NEC in any way they see fit. We run into code legal things that an AHJ will not accept quite frequently.

But theoretically they would need to have an amendment in writing, they can't just say "no we don't allow that". Of course I understand in practice some probably do say that

 

[pv_n00b]

An AHJ has the ability to amend/enforce the NEC in any way they see fit. We run into code legal things that an AHJ will not accept quite frequently.

This depends on the state. In CA AHJs have to apply the adopted codes. They don't get to make their own rules and if they do they can get dope slapped by the boss. Sometimes you just have to go over the head of a stubborn inspector who wants to make their own rules.
But they might do things differently in Texas and allow more liberal local control.

 

[pv_n00b]

This brings up an interesting question. My understanding is that in the NEC there is no distinction between a panel board and a residential main panel (load center). However, I'm wondering if the phrase "switchgear, switch-boards, and panelboards" was purposefully used to imply larger services.

What is your reasoning behind recommending more than 120% on larger panels but not smaller residential panels, if you don't mind me asking?

The code does not differentiate between panelboard uses that I know of when applying this code section.
Part of the reason for the 120% rule is to limit heat buildup in the enclosure. This is not talked about a lot since the ampacity of the bus gets everyone's focus. Switchboards and switchgear are larger, have more volume inside, and have better airflow. It's harder to get in trouble with heat buildup and nuisance tripping when doing a design under engineering supervision. The engineer can just focus on making sure the ampacity on the bus is not exceeded. Thermal problems in panelboards where everything is tight and there is little airflow are just harder to predict.

 

[pv_n00b]

We are trying to apply this code section, with the PV breaker at the end of the busbar in one gear section that has the bussing between sections connecting in the center of the busbar at all distribution sections. We have an EE stamped approval and the AHJ is not very receptive toward the idea, but is not completely unwilling to entertain it.

@pv_n00b - can you share what AHJ has accepted the application of 705.12(B)(3)(5)?

We are under NEC 2017 for our project (permitted before 1/1/23 when the AHJ adopted 2020 code), but rely on 705.12(B)(3)(e) in the same manner.

I don't have a list. Under the 2017 and previous codes, it's not explicitly called out so it calls for more of a discussion with the AHJ. It's not called out how to treat SWBDs and SWGR. Some AHJs are more receptive than others but I have found that if you just talk to people and try to get them to be comfortable with it they will accept it. Getting the PE in the conversation is probably going to help.

 

[don_resqcapt19]

This depends on the state. In CA AHJs have to apply the adopted codes. They don't get to make their own rules and if they do they can get dope slapped by the boss. Sometimes you just have to go over the head of a stubborn inspector who wants to make their own rules.
But they might do things differently in Texas and allow more liberal local control.

I don't think it depends on the state....no AHJ or other authority can enforce any type of requirement that has not been legally adopted.
The real issue, is if it is really worth it to go over their heads.
Unless there is a huge cost involved, most of the time it is simpler to comply, but there have been civil malicious prosecution law suits to recover costs of the enforcement of illegal requirements. In those cases, the EC completed the job and installed according to the wishes of the AHJ, but went to court after the project was completed and recovered the costs associated with complying with the illegal requirement.
After you do that you might not want to work in that jurisdiction for some time

 

[Sberry]

Has this been changed in 2023?

 

[jaggedben]

Has this been changed in 2023?

No.

The provision for engineering supervision to apply to special situations has been in the code since 2014. It's been tweaked in various ways, but has not essentially changed.

 

[Sberry]

I was basically refering to the conductor sizing as I recal, I see a post about 690 below this. I was just curious what the major changes were regarding 2020 and 2023, my inspector bud was babbling something about 23 clearing up a lot of issues but I really didnt grasp what they were.

 

[pv_n00b]

Has this been changed in 2023?

It changed in 2020. In 2017 and previous NECs the provision for sizing busbars, the 120% rule, was limited to panelboards. Engineering supervision was limited to multiple-ampacity busbars only. Applying engineering supervision to SWBDs and SWGR was not mentioned in 705.12 and was totally up to the AHJ's acceptance. This was significantly rewritten in 2020 to widen the applicability of the 120% rule and what engineering supervision applied to.

 

[pv_n00b]

I don't think it depends on the state....no AHJ or other authority can enforce any type of requirement that has not been legally adopted.
The real issue, is if it is really worth it to go over their heads.
Unless there is a huge cost involved, most of the time it is simpler to comply, but there have been civil malicious prosecution law suits to recover costs of the enforcement of illegal requirements. In those cases, the EC completed the job and installed according to the wishes of the AHJ, but went to court after the project was completed and recovered the costs associated with complying with the illegal requirement.
After you do that you might not want to work in that jurisdiction for some time

I was joking about Texas, since ggunn has provided examples of AHJs there just doing their own thing and ignoring changes in the code. The problem with going over the inspector or plan reviewer's head is that often the boss has the same ideas. Then it's a matter of how high up do you have to go. Eventually, as you said the court system is the only option. But most contractors are not interested in doing that due to the huge cost involved. If you are not going to recover $100,000, a large part of which will go to feed the lawyers, it's not really worth it.