New PV group is forming for NEC 2020 690, 691, and 705 proposals.

[pv_n00b]

It is that time again—the 2020 National Electrical Code (NEC) cycle. The old PV Industry Forum, that has existed in one form or another for over 25 years, is gearing up again. This year two organizations will support the PV Industry Forum effort: the PV Industry Code Council (PVICC), and the Solar Energy Industries Association (SEIA). Also included in this effort will be members of the Large-scale Solar Association (LSA).

This meeting is being hosted again by the National Renewable Energy Laboratory (NREL) Energy Systems Integration Facility (ESIF) in Golden, Colorado on April 4-5, 2017. The meeting will have a full agenda for both days with possible breakout sessions once we get through the initial Public Input (PI) list. Plan to be at the NREL site from 8am to 5pm each day.

If you are planning on attending this meeting you MUST RSVP. Please contact PVICC through the website to RSVP. We need to have an accurate count and name list for access to the NREL site. Those who are not U.S. Citizens need to obtain the proper forms that will be necessary to gain access to the laboratory, allow time for this. NREL will need at least two weeks notice prior to the meeting dates in order to review the documents.

Hopefully we will have several members of Code Making Panel 4 (CMP4) in attendance at this meeting. CMP4 has been named the “Renewables” code panel which is destined to continue to raise the prominence of PV in the NEC (even beyond the cover of the 2017 NEC). Everyone is reapplying to CMP4 and we will have a new chair and hopefully several new members with PV experience. News about the makeup of CMP4 should be available before the April meeting.

This is a big honor to be hosted at the ESIF facility. I’m sure we will arrange tours of the ESIF for those who are interested. Special thanks again to NREL for hosting this meeting.

 

[Anode]

It is that time again—the 2020 National Electrical Code (NEC) cycle. The old PV Industry Forum, that has existed in one form or another for over 25 years, is gearing up again. This year two organizations will support the PV Industry Forum effort: the PV Industry Code Council (PVICC), and the Solar Energy Industries Association (SEIA). Also included in this effort will be members of the Large-scale Solar Association (LSA).

This meeting is being hosted again by the National Renewable Energy Laboratory (NREL) Energy Systems Integration Facility (ESIF) in Golden, Colorado on April 4-5, 2017. The meeting will have a full agenda for both days with possible breakout sessions once we get through the initial Public Input (PI) list. Plan to be at the NREL site from 8am to 5pm each day.

If you are planning on attending this meeting you MUST RSVP. Please contact PVICC through the website to RSVP. We need to have an accurate count and name list for access to the NREL site. Those who are not U.S. Citizens need to obtain the proper forms that will be necessary to gain access to the laboratory, allow time for this. NREL will need at least two weeks notice prior to the meeting dates in order to review the documents.

Hopefully we will have several members of Code Making Panel 4 (CMP4) in attendance at this meeting. CMP4 has been named the “Renewables” code panel which is destined to continue to raise the prominence of PV in the NEC (even beyond the cover of the 2017 NEC). Everyone is reapplying to CMP4 and we will have a new chair and hopefully several new members with PV experience. News about the makeup of CMP4 should be available before the April meeting.

This is a big honor to be hosted at the ESIF facility. I’m sure we will arrange tours of the ESIF for those who are interested. Special thanks again to NREL for hosting this meeting.

Would love to go, but for those of you that are, can I just make a wish to see 705.12(D)(2)(3)(b) change to 150%! Yahoo! That would be great Or at least remove the rating of the overcurrnent protection device part...

heh heh, I will keep wishing..

 

[jaggedben]

Are there any particular qualifications that are required or recommended in order to attend?

 

[310 BLAZE IT]

Please definite the circuit conductors between line side connection and PV service disconnect.

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[ggunn]

Please definite the circuit conductors between line side connection and PV service disconnect.

Yeah, it would be great if the NEC would unambiguously require the AC disco next to the POI of a line side interconnection to have a N-G bond, or not. I really don't care which.

 

[Carultch]

Yeah, it would be great if the NEC would unambiguously require the AC disco next to the POI of a line side interconnection to have a N-G bond, or not. I really don't care which.

I would prefer if the NEC would simply unambiguously require the neutral-to-ground bond at every transformer secondary, or at the nearest ground-level piece of equipment which has a grounding electrode connection. Because that is the only place where it makes physical sense, to do it. To define the neutral to be at the same absolute voltage as ground, where that particular voltage system is first derived.

 

[ggunn]

I would prefer if the NEC would simply unambiguously require the neutral-to-ground bond at every transformer secondary, or at the nearest ground-level piece of equipment which has a grounding electrode connection. Because that is the only place where it makes physical sense, to do it. To define the neutral to be at the same absolute voltage as ground, where that particular voltage system is first derived.

We pretty much do that already, don't we? Any time a transformer generates a separately derived system, there is a new ground.

What ties a lot of us in knots is when there is a line (supply) side interconnection. Some AHJ's want a N-G bond in the disco and a GEC from there to a rod with no EGC back to the service, others want it to be the same as if it were a load side connection with no GEC at the switch and an EGC through the switch back to the service. We have "discussed" it ad nauseum in here, but there is no clear compliance or safety concern either way as far as I can tell.

 

[pv_n00b]

Are there any particular qualifications that are required or recommended in order to attend?

It helps if you have a good background in the code and its application, particularly the PV related parts. But even if someone has only an overview of the code it’s a great way to learn how the process works. I’ve learned a lot from my involvement in the code making process over the last decade. Plus you meet some great people.

 

[pv_n00b]

Would love to go, but for those of you that are, can I just make a wish to see 705.12(D)(2)(3)(b) change to 150%! Yahoo! That would be great Or at least remove the rating of the overcurrnent protection device part...

heh heh, I will keep wishing..

Well, it’s changed to 705.12(B)(2)(3)(b) in the 2017 code, but still says the same thing. There has been a lot of discussion over this through the years. It’s ranged from using 100% to 200% and settled on 120%. That’s more due to the legacy of residential panels assumed to be only loaded to 80% taking diversity into account than anything else. So in theory the panel is never loaded over 100% with the PV back feed. The problem with loading it higher is not the current in the bus exceeding the rating, it’s the amount of heat generated and dumped into the panel that needs to be dissipated.

If a 240/120V 200A panel with 200A of load has the capacity to carry 48kVA and is 99% efficient it will max out at a 480W heat load. Now if we put double that power through it and double the load, 200A from the utility and 200A from PV fed from opposite ends then it will have a heat load of 960W. If it’s only designed to dissipate 480W then it’s going to cook the breakers, even though no point on the bus would see more than 200A. That’s the bottleneck.

 

[PWDickerson]

pv_noob, I like your logic, but I disagree with your assumptions, specifically the 99% efficient part. If we assume that the bus bar of a typical 200 amp residential panel has the same cross section as the service conductors, we can do a quick voltage drop calculation and see that the heat dissipated at the bus bar is no where near 480 watts. A 4/0 AL conductor has a resistance of .0001 ohms per foot (Ch. 9, table 9). At 200 amps, this gives a voltage drop of .02V/foot x 200 amps = a heat dissipation of 4 watts per foot, or about 8 watts in a typical 24" long bus bar. Keep in mind that this assumes 200 amps of current through the entire bus bar, which you wouldn't get if you were feeding 200 amps of current into both ends of a busbar, because the current is being diverted into the branch breakers as you approach the middle of the bus.

It seems like the worst case scenario would be where you have feed through lugs at the bottom of your bus bar drawing the full 200 amps, and no loads at your branch breakers, and I would think that a load center capable of being set up like this would in fact be tested under these conditions. This scenario would dissipate almost twice as much heat as a 200 amp panel with 200 amps of PV connected at the opposite end of the bus from the main breaker. Of course you will also have heat dissipation at the stabs, but presumably they are rated for it.

In short, I think the 120% rule is too conservative.

 

[jaggedben]

The resistance of plug on connections is surely much greater than anything internal to busbars or conductors and is where things will heat up to the point of causing any problems that were to occur.

With that said I agree that the 120% rule seems too conservative.

 

[310 BLAZE IT]

Well, it’s changed to 705.12(B)(2)(3)(b) in the 2017 code, but still says the same thing. There has been a lot of discussion over this through the years. It’s ranged from using 100% to 200% and settled on 120%. That’s more due to the legacy of residential panels assumed to be only loaded to 80% taking diversity into account than anything else. So in theory the panel is never loaded over 100% with the PV back feed. The problem with loading it higher is not the current in the bus exceeding the rating, it’s the amount of heat generated and dumped into the panel that needs to be dissipated.

If a 240/120V 200A panel with 200A of load has the capacity to carry 48kVA and is 99% efficient it will max out at a 480W heat load. Now if we put double that power through it and double the load, 200A from the utility and 200A from PV fed from opposite ends then it will have a heat load of 960W. If it’s only designed to dissipate 480W then it’s going to cook the breakers, even though no point on the bus would see more than 200A. That’s the bottleneck.

Doesn't the 120 percent rule just allow the extra 20 percent because there is an 80 percent rated breaker so the bus has the extra capacity? If this is the case I'm about to use the 120 percent rule on a job with all 100 percent breakers and I'm not sure the code adequately protects the installation. While it always comes down to heat, that should be considered in the listing process and not the code.

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[ggunn]

Doesn't the 120 percent rule just allow the extra 20 percent because there is an 80 percent rated breaker so the bus has the extra capacity? If this is the case I'm about to use the 120 percent rule on a job with all 100 percent breakers and I'm not sure the code adequately protects the installation. While it always comes down to heat, that should be considered in the listing process and not the code.

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705.12 makes no distinction between 80% and 100% rated breakers.

 

[310 BLAZE IT]

705.12 makes no distinction between 80% and 100% rated breakers.

What I'm saying is it should... or it should have a separate section for switchboard/switchgear. It should use the same exception used in 690

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[jaggedben]

(You saw the responses in your other thread, right?)

 

[310 BLAZE IT]

(You saw the responses in your other thread, right?)

Sorry about that... I'll keep it to one thread

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