705.12(B)(3)(2) Busbar 120% Rule: What are LOADS?

[nsitzman]

I have one of Mikes older 2014 NEC videos covering PV connections bookmarked as it an excellent training video to brush up on interconnected sources when I feel rusty or a new question/interpretation comes up (

). I re-watched it yesterday as a question about the 120% rule for busbars came up in my jurisdiction. This topic is covered in the video (this starts at 55:25 in the video) under 705.12(D)(2)(3)(b) of the 2014 NEC, which still lives on as 705.12(B)(3)(2) in the 2020 NEC and states "Where two sources, one a primary power source and the other another power source, are located at opposite ends of a busbar that contains loads, the sum..."

The video does not show any load breakers on the busbar or feeders from the MLO panel to any loads, just the back-fed PV OCPD's, but this may be for clarity. The question that has come up in my jurisdiction is What constitutes a "load" for the purpose of this code section? Does this mean the 120% rule can not be applied if there are no breakers installed on this panelboard that serve 'active' loads? What if the only 'load' is a single pole circuit for a general purpose duplex receptacle off the side of the panelboard enclosure? Does the feeder from an MLO panelboard count as a "load" for the purpose of this code section even if there aren't breakers on the busbar? Does Mike have a newer video, or is there already a thread, that addresses this?

It seems that it might be splitting frog hairs to some, but words mean things. Sometimes the easy to overlook minutia in the NEC has a tremendous impact on correctly interpreting the code. With the new 2020 NEC requirements for the exterior disconnect, I see this becoming a more common occurrence/issue as installers are now using meter main type exterior panels as the norm rather than the exception. Thanks in advance for any direction on this!
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REPLY

 

[pv_n00b]

You seem to be overthinking this. If you have a panelboard that you can put circuit breakers in then it is capable of supplying loads. It does not matter if there are breakers installed currently. If the PV system is installed today in an empty panel then the 120% requirement can still be applied. Because tomorrow someone will install a load breaker.

 

[wwhitney]

You seem to be overthinking this. If you have a panelboard that you can put circuit breakers in then it is capable of supplying loads. It does not matter if there are breakers installed currently.

The quoted wording of 705.12(B)(3)(2) does not support that interpretation, it refers to the present configuration, not what is possible.

However, I believe any busbar that would comply with 705.12(B)(3)(2) but contains no loads would automatically comply with 705.12(B)(3)(3) (the 100% rule).

Cheers, Wayne

 

[pv_n00b]

The quoted wording of 705.12(B)(3)(2) does not support that interpretation, it refers to the present configuration, not what is possible.

However, I believe any busbar that would comply with 705.12(B)(3)(2) but contains no loads would automatically comply with 705.12(B)(3)(3) (the 100% rule).

Cheers, Wayne

Good luck with that interpretation and an AHJ. "But there are no loads on it now, what do you mean I have to follow the NEC anyway? Oh, you noticed that box of breakers I will install tomorrow in this panel for loads? Please don't notice that"

 

[pv_n00b]

You have several options for looking at it if you have an empty panel that you just want to put a PV back feed CB in.

1. You can go by 705.12(B)(3)(1). But if the panel has available spaces for load CBs you are going to have to convince the AHJ they will never be used. Maybe add signage saying "Additional CBs shall not be installed in this panel" to maintain compliance with the NEC section. Because AHJs know, and you should too, someone will want to use an empty space to put in the load CB if it is convenient for them in the future.
2. You can go by 705.12(B)(3)(2). You don't need to know the loads in the panel to apply this section only that they exist, or may exist in the future. Someone can come along later and add load CBs with no worries about additional requirements for compliance with this section. If you want to be pedantic you can say this section only applies if there are load CBs in the panel and can't be used in a panel without load CBs. But frankly, that would go against over a decade of industry interpretation. But you be you.
3. You can go by 705.12(B)(3)(3). Make it an AC aggregation panel for a PV system. No loads are required and any loads added later need to comply with this section.

 

[wwhitney]

Good luck with that interpretation and an AHJ.

What are you talking about?

The situation the OP describes is something like a 100A main breaker panel with 100A bus and only one distribution breaker in it, a 20A PV breaker at the opposite end of the bus. And the concern was that the 120% rule only applies to "a busbar that contains loads," so that without any load breakers, the panel wouldn't conform with the letter of the rule. A technical violation.

So I was just pointing out that the panel would comply with the 100% rule now. And that's all that matters to resolve the technical violation. Obviously if you add breakers in the future you'd need to follow one of the rules. But if you are adding loads breakers, you could add as many as you want, since it will then comply with the 120% rule.

Cheers, Wayne

 

[pv_n00b]

Does this mean the 120% rule can not be applied if there are no breakers installed on this panelboard that serve 'active' loads?

You could say that but it goes against over a decade of industry interpretation. It's kind of a settled interpretation that it means existing or future loads.

What if the only 'load' is a single pole circuit for a general purpose duplex receptacle off the side of the panelboard enclosure?

That's a load

Does the feeder from an MLO panelboard count as a "load" for the purpose of this code section even if there aren't breakers on the busbar?

I'm going to assume you mean a feeder "to" an MLO panel from a CB in the panel we are going to back feed. That's a load CB. It's a source or a load, there are no other types.

Does Mike have a newer video, or is there already a thread, that addresses this?

No, because this is already well understood and accepted by the industry.

It seems that it might be splitting frog hairs to some, but words mean things.

You are. But lots of people do that here Words in the NEC do not always mean the same thing as words we use every day.

Sometimes the easy to overlook minutia in the NEC has a tremendous impact on correctly interpreting the code.

Keep in mind that you or I not understanding part of the code does not mean there is a misunderstanding in the industry. Also, some well-established code interpretations don't make sense to me either, but I accept that they are well established and go with it.

Good luck. I know it's confusing. We are from the government and we are here to help.

 

[jaggedben]

Good luck with that interpretation and an AHJ. "But there are no loads on it now, what do you mean I have to follow the NEC anyway? Oh, you noticed that box of breakers I will install tomorrow in this panel for loads? Please don't notice that"

Wayne is correct about automatically comply with 705.12(B)(3)(3). (That is, provided we assume that the panel and breakers comply with other relevant code requirements. i.e. 705.28 and 705.30). His conclusion is logically entailed by the various requirements, even if not spelled out in the language.

My only quibble is calling 705.12(B)(3)(3) 'the 100% rule', as that phrase is ambiguous between 705.12(B)(3)(3) and 705.12(B)(3)(1). I call (3) the 'sum of all breakers' rule.

 

[jaggedben]

You have several options for looking at it if you have an empty panel that you just want to put a PV back feed CB in.

1. You can go by 705.12(B)(3)(1). But if the panel has available spaces for load CBs you are going to have to convince the AHJ they will never be used. Maybe add signage saying "Additional CBs shall not be installed in this panel" to maintain compliance with the NEC section. Because AHJs know, and you should too, someone will want to use an empty space to put in the load CB if it is convenient for them in the future.

705.12(B)(3)(1) doesn't restrict loads whatsoever.

 

[Solar Guy]

If you are not going to put any load breakers in the panel, why have the panel? Just feed the inverters' combined output straight to the service entrance as a line-side tap through a fused/ breakered customer visible disconnect.

There is some logic to the rule that two sources at the ends of a panel's bus can add to more than the panel's rating, but not more than 120% of it. That is because it is assumed there will be load breakers between the two sources which will bleed off some of the available current, such that no place on the bus sees more than its rating - or if it does, it is probably transient such as a motor starting. That's why the two supply breakers must be at opposite ends. At least that's my take on it.

 

[ggunn]

A situation we encounter frequently is where a 200A feedthrough panel with no loads is installed out at a pole mounted utility revenue meter instead of a 200A disco. Perhaps they are cheaper? We typically treat it like a switch and post a "DO NOT INSTALL LOADS" placard on the deadfront.