Term for PV dedicated panels

[Engineer#4827502]

What terms do you all use for panelboards/switchboards that are dedicated to aggregating inverter outputs? Is anyone aware of an accepted industry standard term?

I've seen the following (and other variations) used:

• Inverter Aggregation Panelboard
• Collection panelboard
• Inverter AC combiner
• Photovoltaic/PV/solar panelboard

I think any of those terms generally convey that the panel is only connected to interter outputs but I was wondering if anyone is aware of an industry standard. Supposedly the 2017 NEC will address these types of panels more specifically, though I have not seen any of the language yet. Thoughts?

 

[Carultch]

What terms do you all use for panelboards/switchboards that are dedicated to aggregating inverter outputs? Is anyone aware of an accepted industry standard term?

I've seen the following (and other variations) used:

• Inverter Aggregation Panelboard
• Collection panelboard
• Inverter AC combiner
• Photovoltaic/PV/solar panelboard

I think any of those terms generally convey that the panel is only connected to interter outputs but I was wondering if anyone is aware of an industry standard. Supposedly the 2017 NEC will address these types of panels more specifically, though I have not seen any of the language yet. Thoughts?

AC Combiner, or AC combining panelboard, is the term we use at my company.

BTW, NEC2017 is now available for online viewing.


One thing I wonder about is whether or not the panelboard is still "dedicated" to the PV system, when loads such as rapid shutdown power supplies, surge arresters, or metering voltage taps, are wired to branch circuits. I'd like to see these negligible load breakers justified to be in the panel, even if dedicated to inverters.

 

[Engineer#4827502]

Thanks for the tip on 2017 code. It's here if anyone else needs:

http://www.nfpa.org/codes-and-stand...list-of-codes-and-standards?mode=code&code=70

I looked through and can't find anything....

Putting small loads on an otherwise PV generation dedicated panelboard shouldn't cause any safety issues. It would be nice if the NEC addressed these issues explicitely. Is the 2017 NEC online the final version or are any more revisions expected?

 

[ggunn]

We call them "solar load centers".

 

[jaggedben]

From the 2014 Code's perspective, it doesn't matter what you call it as long as you apply the warning label required by 705.12(D)(2)(3)(c).

This provision was put in I believe to clarify how (what I call) AC combiners can be permitted without requiring the 120% rule. However from the Code's point of view they are not strictly dedicated and have no defined term applied to them. You can put a load in them (e.g. monitoring system) without arguing with an AHJ about what it means to be dedicated, which is a good thing. And someone can come along later and put an unrelated load into them, but if they ignore and violate the warning label then that code violation would be on them.

I actually think this way of addressing AC combiners is quite decent and I don't really think the code needs additional language to address or define them. As far as communicating within the industry, any of the terms mentioned in this thread is fine by me. FWIW, Enphase uses the term 'AC combiner' for their product designed for the purpose, which is about the most 'official' industry endorsement of any term I can think of. Adding 'Solar' or 'PV' to the front might help in some cases.

 

[Carultch]

From the 2014 Code's perspective, it doesn't matter what you call it as long as you apply the warning label required by 705.12(D)(2)(3)(c).

This provision was put in I believe to clarify how (what I call) AC combiners can be permitted without requiring the 120% rule. However from the Code's point of view they are not strictly dedicated and have no defined term applied to them. You can put a load in them (e.g. monitoring system) without arguing with an AHJ about what it means to be dedicated, which is a good thing. And someone can come along later and put an unrelated load into them, but if they ignore and violate the warning label then that code violation would be on them.

I actually think this way of addressing AC combiners is quite decent and I don't really think the code needs additional language to address or define them. As far as communicating within the industry, any of the terms mentioned in this thread is fine by me. FWIW, Enphase uses the term 'AC combiner' for their product designed for the purpose, which is about the most 'official' industry endorsement of any term I can think of. Adding 'Solar' or 'PV' to the front might help in some cases.

The one issue I have with the "sum of the breakers" rule, is that it requires you to accumulate rounding errors, on a panelboard with most of the branch circuits being inverter sources, and not even an ampere being a load. Example: 25A of inverter = 31.25A required for sizing the breaker, which then prompts a 35A breaker. Now add this up for the numerous inverters in the panel, and accumulating the rounding errors means planning for amperes that are never going to exist.

In small applications, it's probably no issue. But when you have a dozen inverters, accumulating rounding errors can make the difference between a 600A and an 800A panelboard.

The "sum of the breakers" rule is a good rule on a mixed use panelboard that could be half inverters, and half loads. Like a critical loads panelboard in an off-grid application.

 

[jaggedben]

Fair point. Although certainly if you have loads then it makes more sense to go by breaker size. For some reason the CMP seems to have a bias against a 'no loads allowed' warning label, and prefers this approach. My recollection is that a 'no loads' rule has been proposed more than once and always rejected. Why they think this warning label would be more effective I can only speculate about. Of course it's also an advantage being able to put monitoring loads into a panel without having to discuss whether that type of load is okay or not.

Another grey area is if you have an AC combiner connected to a supply side connection that is not supposed to be used for normal service loads. (Let's say it's the seventh disconnecting means.)

On balance I still think this was a decent way to address the issue without having to add a whole page worth of caveats and definitions to the code. Even using the breaker value is an improvement over having to meet the 120% rule, which 2011 could be read to require.

 

[pv_n00b]

I have always labeled them AC Combiners.

The "No Loads Allowed" marking has been rejected over and over because the CMP thinks that it will either be obscured, fall off, or just plain ignored. Anyway I've seen so many "dedicated" AC combiners that have PV related loads in them that it is clear PV folks will ignore it so maybe they have a point.

It's definitely an improvement over the alternative 120% guidance.

 

[ggunn]

The one issue I have with the "sum of the breakers" rule, is that it requires you to accumulate rounding errors, on a panelboard with most of the branch circuits being inverter sources, and not even an ampere being a load. Example: 25A of inverter = 31.25A required for sizing the breaker, which then prompts a 35A breaker. Now add this up for the numerous inverters in the panel, and accumulating the rounding errors means planning for amperes that are never going to exist.

Be that as it may, it's a huge improvement over the 2011 code where you either had to make the panel nearly twice the size it needed to be (the 120% rule) or get the AHJ to turn a blind eye to what was technically a violation. I rarely if ever encounter a situation where a larger panel has to be used due to rounding errors; that's a pretty narrow window to worry about.

BTW, the AHJ we operate mostly with has decided that a breaker in a solar load center (the term we use for it) that connects a surge protection device to a system is not counted either as a source or a load.

 

[SolarAlternativesDesign]

Regarding 2014 705.12(D)(1), "The source interconnection of one or more inverters installed in one system shall be made at a dedicated circuit breaker or fusible disconnecting means." What about connecting the inverter output circuit to a backfed PV breaker at the bottom of an AC subpanel that has load breakers in it? In that case is the connection considered a dedicated circuit breaker? It looks to me like the service panel breaker protecting the subpanel isn't dedicated to the PV. Is that a problem? :?

Also regarding the sum of the breakers rule, 2014 705.12(D)(2)(3)(a) get us away from the sum of the breakers by permitting "The sum of 125% of the inverter(s) output circuit current and the rating of the overcurrent device protecting the busbar shall not exceed the ampacity of the busbar.", but with that calculation method it doesn't permit '120% of the ampacity of the busbar.' Is 705.12(D)(2)(3)(a) more permissive than the 120% rule of 705.12(D)(2)(3)(b) in some cases but not others?

 

[ggunn]

... regarding the sum of the breakers rule, 2014 705.12(D)(2)(3)(a) get us away from the sum of the breakers by permitting "The sum of 125% of the inverter(s) output circuit current and the rating of the overcurrent device protecting the busbar shall not exceed the ampacity of the busbar.", but with that calculation method it doesn't permit '120% of the ampacity of the busbar.' Is 705.12(D)(2)(3)(a) more permissive than the 120% rule of 705.12(D)(2)(3)(b) in some cases but not others?

The difference is where the backfed breaker is mounted. If 125% of the inverter output current plus the rating of the main breaker is less than 100% of the busbar rating, you may put the backfed breaker anywhere you want to in the panel. If that sum is between 100% and 120% of the rating of the busbar, the backfed breaker must be at the opposite end of the busbar from the main breaker. If it is more than 120% of the busbar rating, then you must consider other alternatives.

 

[SolarAlternativesDesign]

Yeah, I just noticed that 705.12(B)(2)(3)(b) permits "the sum of 125% of the inverter(s) output circuit current rating​ and the rating of the overcurrent device protecting the busbar shall not exceed 120% of the ampacity of the busbar" if the PV breaker is at the opposite end. I think this frees us from the sum of the breakers problem, doesn't it?

 

[jaggedben]

Yeah, I just noticed that 705.12(B)(2)(3)(b) permits "the sum of 125% of the inverter(s) output circuit current rating​ and the rating of the overcurrent device protecting the busbar shall not exceed 120% of the ampacity of the busbar" if the PV breaker is at the opposite end. I think this frees us from the sum of the breakers problem, doesn't it?

Yes the sum of the breakers problem only applies now to the next section, 705.12 (D)(2)(3)(c).

 

[jaggedben]

.... If 125% of the inverter output current plus the rating of the main breaker is less than 100% of the busbar rating, you may put the backfed breaker anywhere you want to in the panel. ....

Somewhat more importantly, you can leave the main breaker anywhere you want.

 

[Anode]

Throwing in the two cents

In the past we have also called them "Dedicated PV Panel", "AC Combiner Panel", "PV Load Center". I think the main thing is ensuring you have a big label that says do not add loads, and maybe another one that says, no really do not add loads... Have a code reference stickered there.

The naming convention we use is "PV1, PV2, etc."

 

[ggunn]

Throwing in the two cents

In the past we have also called them "Dedicated PV Panel", "AC Combiner Panel", "PV Load Center". I think the main thing is ensuring you have a big label that says do not add loads, and maybe another one that says, no really do not add loads... Have a code reference stickered there.

The naming convention we use is "PV1, PV2, etc."

If you qualify the busbars under 705.12(D)(2)(3)(c), which is the language that legitimizes the AC combiners many of us have been building for years without counting the panel OCPD rating toward the 120% rule, you can have a mix of supply and load breakers.

 

[SolarAlternativesDesign]

If you qualify the busbars under 705.12(D)(2)(3)(c), which is the language that legitimizes the AC combiners many of us have been building for years without counting the panel OCPD rating toward the 120% rule, you can have a mix of supply and load breakers.

That goes a long way to clarifying my question about the dedicated breaker requirement, but it seems like the wording of the NEC is a little murky on this.

705.12(D)(2)(3)(c) permits the backfed PV breaker and load breakers on a panelboard to total up to 100% of the rating of the busbar (as long as no one adds more breakers to bring the total above the busbar rating). This makes sense logically. No 120% factor is allowed in this case, which is clear. This doesn't say explicitly that the 705.12(D)(1) requirement for a dedicated breaker does not apply, but it does say that implicitly, doesn't it? Are installers able to work out things like this with inspectors?

Thanks for clarifying this!

 

[jaggedben]

The dedicated breaker rule always applies, you're just overinterpreting it's meaning. The point of the dedicated breaker rule is that loads cannot be on the same breaker as a source. It is not supposed to mean that all sources have to be on one breaker. Hranted the code language is a little vague and this could be argued over, but that's how I see it.

Now if you have so many sources that they can't all fit on the opposite end then you arguably can't take advantage of the 120% rule. The most I see one getting away with is four sources on two quad breakers on the last two stabs.

 

[SolarAlternativesDesign]

Your interpretation makes more sense. Thanks for the explanation.

 

[Zee]

We used to call them (Photovoltaic) Accumulation Panels. :huh: