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Question about 120 percent NEC rule with Tesla Gateway 2

wwhitney

Member
Nov 2, 2017
898
1,184
Berkeley, CA
Option 1: Ask them to make a generation panel that feeds the TEG2 internal panelboard. But if they use a panel like this; why wouldn't they just put the 3x 30A and 1x 35A double poles into it? Then I could plug this generation panel directly to the bottom lugs on the TEG2. I'm trying to understand the benefit of putting only the Powerwalls into a sub panel and then running the 35A separately onto the TEG2 internal panelboard.

A generation panel with everything in it will also provide the benefit of piping through a big-lever-switch outside of my house. This way the inspector sees the big lever (can't claim glove-hands!) instead of BR style breakers.
So if you want the big lever, then a 125A generation panel in the garage that has (3) 30A Powerwall breakers and (1) 35A PV breaker makes a lot of sense. And then there's no need for the interior panelboard in the TEG2.

But if you're willing to forego the big lever, then you can replace the big lever with the TEG2 interior panelboard with a single 125A breaker. That becomes your shutoff.

Or the TEG2 interior panelboard could have a 90A and a 35A, and the garage generation panelboard could be Powerwalls only. Then you have two shutoff breakers in the TEG2. It's just a question of whether you'd like the feeder for the Combiner to originate from inside the garage, or from the TEG2.

Any of those will work.

Cheers, Wayne
 

holeydonut

Supporting Member
Jun 27, 2020
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East Bay NorCal
Sweet thanks for the extra info.

I need to play this as safe as possible. The big ugly lever seems to be what most old timey inspectors may expect. This will basically be near where I store my trash bins so I don’t care what it looks like.
 

Vines

Active Member
Jul 20, 2018
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Silicon Valley, CA
I took some time away from the computer, so looking back at this saga I think you have what you need from Wayne.

The quads and main breakers are currently made of unobtanium, so the quad solution isn't the quick one. The big bladed lockable isn't really needed, and useless as you point out where it is currently shown electrically by Sunrun (except as a utility disconnect of generation sources from grid).
 

holeydonut

Supporting Member
Jun 27, 2020
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East Bay NorCal
Hi Vines,

Sounds like you’re agreeing with Wayne that I should not run the 90A and 70A home loads off of the internal panelboard like in that drawing I updated.

The funny thing is my house had run with two OCPD on the same busbar in my main panel for years- there was no main OCPD over the top of them anywhere.

But I guess now If the same circuits are on the internal panel board I’d need a 200A with them on the Gateway.

Im sure some inspector somewhere is going to crap in this install even if I use the big bladed disconnect to interrupt the PV and ESS.
 

Vines

Active Member
Jul 20, 2018
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Silicon Valley, CA
I agree not having a main breaker in your backup loads panel is not the most code compliant way to approach this. You say you want to be bulletproof safe, and what you suggest is not.

Because a backup load panel can be fed from power from 2 sources, it has the potential to be overloaded. You have a 3rd slot there and someone poorly trained comes along and installs a 100A breaker for a pair of car chargers subpanel inside that subpanel. Now it has a total breaker rating of 260A and its not obvious to them there would be any issue.

Once there are 260A worth of breakers on the bus there is also nothing to stop them drawing 260A, through a 200A panel. Usually this is taken care of at the 200A Main breaker, draw more than 200A and it pops. Now with PW + PV you can draw 200A from the grid and another 125A from the PV and Powerwalls. Because the Gateway 2 has a power control system, it can even control this very finely and get you into trouble where normally it would just pop the main 200A breaker due to a demand spike.

Before you had Powerwalls, the rules were different with your main panel. Those style panels usually can take a limited selection of breakers. Often its maxed out at 100-125A per stab, or a quad fits too sometimes. Usually there is room for only 2 stabs on the MSP bus.

If you want the fewest pieces, then the Sunrun solution isn't terrible and as long as the PV combiner breakers are outdoors and accessible. The rub is that configuration is not NEC compliant, so you have to convince the inspector that the Powerwalls+PV will not overload the 225A bus and violate the 120% rule. Adding a second 125A generation subpanel, fed by this 225A subpanel could make this solution work with export control enabled, but that's the hard way to do it and IMO more AHJ risk. If you cant convince him that the bladed lockable isn't needed, then convincing him export control is safe will be an uphill battle.

One solution in my eyes since the quads are not available, is to just install a 125A subpanel that can take all the PW breakers next to the PW in the garage. Land the 35A PV combiner directly in this new 125A subpanel, and have the subfeed run outside to a bladed lockable disconnect, and then to the 200A lugs of the TEG. The other 200A lugs in the TEG go to your essential loads panel, which needs a 200A main breaker. This one handle would accomplish battery and PV shutdown, but the downside is that if PGE came out with a lock to do grid maintenance, they would lock out your backup system off.

The more correct way IMO is to omit the bladed lockable disconnect, and replace it with the remote battery disconnect button next to the MSP. Rapid shutdown then simply looks like tripping the main breaker, or pulling the meter, then hitting the button to shut down the PW which shuts down the PV. This way you don't need to run a 125A feeder to the disco and back. This is probably not super difficult of an alternative but I am not your AHJ so I cannot speak for them.
 
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holeydonut

Supporting Member
Jun 27, 2020
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East Bay NorCal
Thanks Vines - as always this is very insightful info.

Since I've faced every hurdle imaginable on this - I agree it makes sense to run as conservative as possible. I can just feel some old-school inspector saying gloved hands cannot operate BR style breakers since those OCPDs are too small. I've been constantly surprised at how much red tape is involved for this PV and ESS tech that seems fairly common now-a-days.

I doubt Sunrun's current line diagram with the blade AC disconnect right after my MSP will pass an inspection for fireman safety. The disconnect doesn't actually do anything to turn off the PV or ESS energy from entering my home since it's outside the gateway. I don't think Enphase's anti-islanding would kick on if someone disabled the blade disconnect the way Sunrun diagramed. And the ESS energy is definitely going to remain live the way Sunrun diagramed my install.

I wonder how many of Sunrun's other customers have the fireman safety AC disconnect outside of their backup gateway, and there is no disconnect for the batteries.

One solution in my eyes since the quads are not available, is to just install a 125A subpanel that can take all the PW breakers next to the PW in the garage. Land the 35A PV combiner directly in this new 125A subpanel, and have the subfeed run outside to a bladed lockable disconnect, and then to the 200A lugs of the TEG. The other 200A lugs in the TEG go to your essential loads panel, which needs a 200A main breaker. This one handle would accomplish battery and PV shutdown, but the downside is that if PGE came out with a lock to do grid maintenance, they would lock out your backup system off.

I think this solution is the most conservative and most likely to pass any BS that someone could throw my way. I'm confused why you think PG&E would need to use the bladed disconnect though. If PG&E came out to do grid maintenance, wouldn't they just shut off the 200 A breaker in the main panel? Why would they need to turn off the bladed disconnect lever as well to disable my generation sources?

I'll recommend a Square D HOM1224L125PGCVP for the indoor mount 125 A generation panel. I know Wayne said a single OCPD protecting generation sources isn't required per se, but adding one can't hurt right?

I updated your diagram with what I think this would look like:
upload_2020-11-29_11-39-12.png
 
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Vines

Active Member
Jul 20, 2018
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Silicon Valley, CA
PGE just does that sometimes when they see a PV system with a bladed AC disconnect nearby. They are just being cautious, and require the same for any generation source with a few exemptions.

The thinking is that if equipment is fried and replacement is required your equipment might be as well. Nothing will get through a bladed lockable and it can always be verified.

The ESS does not require a rapid shutdown, so if contractors are isolating the PV breakers inside with no exterior means of disconnect they are not code compliant, and creating a safety hazard.

If the Enphase combiner is outside, then the PV breakers satisfies code for PV rapid shutdown, barring city or fire amendments requiring ESS shutdown from exterior of the building.

The rest is just noise and a waste of time but might make sure you get by a grumpy inspector or poorly informed contractor representative.

I might omit the main breaker in your generation panel simply because they are not easily available though.
 

holeydonut

Supporting Member
Jun 27, 2020
1,820
1,195
East Bay NorCal
The ESS does not require a rapid shutdown, so if contractors are isolating the PV breakers inside with no exterior means of disconnect they are not code compliant, and creating a safety hazard.

If the Enphase combiner is outside, then the PV breakers satisfies code for PV rapid shutdown, barring city or fire amendments requiring ESS shutdown from exterior of the building.

The rest is just noise and a waste of time but might make sure you get by a grumpy inspector or poorly informed contractor representative.


I agree the ESS shouldn’t need an exterior shutdown, but threads like this one with @jedmo make me think inspectors are looking for anything to fail green energy installs lately.

I didn’t realize there was so much dislike over green stuff going into this project. Between PG&E and the wacky new fire codes... I wonder how anyone is getting a resiliency installed and approved lol.

Failed solar/powerwall inspection
 

holeydonut

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Jun 27, 2020
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East Bay NorCal
FWIW, according to PG&E, molded case circuit breakers are not allowed for the disconnect between the Grid and the distributed energy generation system (which I think includes both solar and ESS).

https://www.pge.com/includes/docs/p...lity/electrictransmission/handbook/060559.pdf

#11: Molded case circuit breakers, pull-out type disconnects, or any other similar device are not acceptable as an approved disconnect switch.


I guess using the Gateway 2 internal panelboard disconnects could work for the fireman safety requirement, but it technically wouldn't work for the PG&E requirement.

The fireman requirement cares to prevent the energy system from reaching your home so the solar inverters anti-islanding has to kick in. And that also presumably means the batteries shouldn't be reaching the home either since the intention is to de-energize the home and make it so no live wires are active anywhere.

The PG&E requirement cares to prevent the energy generation system from reaching their grid so they can safely work on their PoCo stuff.

As @Vines pointed out, if you use the same disconnect for both uses, then PG&E would disable your home backup solution if they ever had to work on services near your home. I guess the "safest possible answer" is to use the Gateway 2 internal panelboard so the fireman requirement is met. And then use the fat lever-box bladed disconnect where Sunrun drew it up for PG&E's requirement.
 

holeydonut

Supporting Member
Jun 27, 2020
1,820
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East Bay NorCal
Iteration number 337 of this stupid project...

The red disconnect is where Sunrun drew it up and works for PG&E. Glove handed PG&E linemen will be pleased.

The purple generation breaker mounted to an outdoors Gateway 2 with a BR2125 would satisfy NEC 2017 690.12 and 705.23 to provide rapid shutdown for both PV and ESS so the house would go dead (except for the energy in the powerwalls). I think this would also activate the anti-islanding feature of the Enphase microinverters.

This wouldn't use a "quad 30" since those are weird looking and potentially could scare an inspector or Sunrun lawyer.

I think everything works for NEC load calcs since it conforms with the 120 rule and has OCPD over the top of my home loads.


upload_2020-11-30_11-56-54.png
 
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wwhitney

Member
Nov 2, 2017
898
1,184
Berkeley, CA
Does PG&E require a disconnect for your project? I know for small solar they don't. I also believe for small storage they don't. But maybe with 3 Powerwalls, you are over 10kW of storage inverter power, and they require a disconnect?

Cheers, Wayne
 

holeydonut

Supporting Member
Jun 27, 2020
1,820
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East Bay NorCal
Does PG&E require a disconnect for your project? I know for small solar they don't. I also believe for small storage they don't. But maybe with 3 Powerwalls, you are over 10kW of storage inverter power, and they require a disconnect?

Cheers, Wayne


That document seems to make it seem like all distributed generation customers need the switch unless they're a special case (not something easily defined by system size or used technology).

https://www.pge.com/includes/docs/p...lity/electrictransmission/handbook/060559.pdf

AC Disconnect Switches for Inverter-Based Generation
(this link is for large-business; but if a 3x Powerwall counts as a large-scale system then I guess it could apply to me?)

Here's their list of approved Eaton disconnects
(since this list goes all the way down to 30 Amps, I feel like everybody needs this regardless of system size. but they include NEMA 1 boxes which shouldn't be used outdoors... very weird.)

Sunrun seems to think the utility disconnect is required since they had it in their line diagram. And PG&E probably wants it operable while wearing gloves. I mistakenly thought Sunrun's diagrammed disconnect was the fireman rapid shutoff requirement.

The PG&E document about this didn't really provide a super-easy-to-read exclusion for "small solar." There was an exemptions list for "self-contained" solar, but at this point I think PG&E will do everything in their power to screw me instead of finding a way for me to get around it haha.

I do have a FM2S CL200 meter so I think everything on the exclusion list makes sense except for the "self-contained" thing. Personally I don't mind a big lever blade locking disconnect thing... and I'm not going to try and work-around it.

The key for me is to find a solution that conforms with both PG&E and NEC 2017 so I don't get poo-poo'd by an inspector. But no, I'm not installing those damn bollards.


Exemption to the Disconnect Switch installation Requirement

Applicants with inverter-based generating systems that are supplied by PG&E single phase services up to 240 volts may be exempted from installing a disconnect switch, as determined by PG&E, if the meter panel that is interconnected with the generation source(s) meets all of the following conditions:
• Self-contained (not transformer-rated).
• Accepts form ”S” socket-based (e.g., FM2S) meters (not bolt-on meters).
• Rated for 320 amps (CL 320) or less of “continuous” current.
• Single-phase, 120/240 volt or 120/208 volt.

Any generation system that does not meet these conditions must install a disconnect switch, as required by PG&E.
 
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Vines

Active Member
Jul 20, 2018
1,896
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Silicon Valley, CA
That document seems to make it seem like all distributed generation customers need the switch unless they're a special case (not something easily defined by system size or used technology).

https://www.pge.com/includes/docs/p...lity/electrictransmission/handbook/060559.pdf

AC Disconnect Switches for Inverter-Based Generation
(this link is for large-business; but if a 3x Powerwall counts as a large-scale system then I guess it could apply to me?)

Here's their list of approved Eaton disconnects
(since this list goes all the way down to 30 Amps, I feel like everybody needs this regardless of system size. but they include NEMA 1 boxes which shouldn't be used outdoors... very weird.)

Sunrun seems to think the utility disconnect is required since they had it in their line diagram. And PG&E probably wants it operable while wearing gloves. I mistakenly thought Sunrun's diagrammed disconnect was the fireman rapid shutoff requirement.

The PG&E document about this didn't really provide a super-easy-to-read exclusion for "small solar." There was an exemptions list for "self-contained" solar, but at this point I think PG&E will do everything in their power to screw me instead of finding a way for me to get around it haha.

I do have a FM2S CL200 meter so I think everything on the exclusion list makes sense except for the "self-contained" thing. Personally I don't mind a big lever blade locking disconnect thing... and I'm not going to try and work-around it.

The key for me is to find a solution that conforms with both PG&E and NEC 2017 so I don't get poo-poo'd by an inspector. But no, I'm not installing those damn bollards.

PGE almost certainly doesn't require a bladed lockable disconnect for your project, sounds like you are installing one anyway and are fine with that.

Installing the 125A main breaker only panel will accomplish all ESS shutdown and PV Rapid Shutdown. Once the TEG doesn't see the 240v line connection to the powerwalls, it automatically shuts down all Powerwall generation through the 12v control conductors, therefore shutting down the PV too.
 
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holeydonut

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Jun 27, 2020
1,820
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East Bay NorCal
PGE almost certainly doesn't require a bladed lockable disconnect for your project, sounds like you are installing one anyway and are fine with that.

Installing the 125A main breaker only panel will accomplish all ESS shutdown and PV Rapid Shutdown. Once the TEG doesn't see the 240v line connection to the powerwalls, it automatically shuts down all Powerwall generation through the 12v control conductors, therefore shutting down the PV too.


Sunrun seems to think my project needs the big ol' bladed disconnect box where it was diagrammed. They said the engineer put the disconnect in the correct part of the diagram since the intention of that disconnect was to isolate my house from the grid, but not interrupt my PV or ESS. They won't remove the blade disconnect even if I asked them to lol.

As you pointed out, they were going to mount the PV breakers on an outside wall, and allow the rapid shutdown of PV via those BR breakers in the Enphase combiner.

They didn't know about the situation that @jedmo posted about in his thread where his installation was rejected since the ESS didn't have a rapid shutdown. I can't tell which AHJs have adopted 2017 NEC 705.23, but that seems to be the culprit requiring rapid shutdown of ESS as well as rapid shutdown for PV under 2017 NEC 690.12.

Lots of fancy boxes and wires! I think that last final diagram I just posted is going to be what is used. Much fun.
 

wwhitney

Member
Nov 2, 2017
898
1,184
Berkeley, CA
They didn't know about the situation that @jedmo posted about in his thread where his installation was rejected since the ESS didn't have a rapid shutdown. I can't tell which AHJs have adopted 2017 NEC 705.23, but that seems to be the culprit requiring rapid shutdown of ESS
705.23 doesn't require "rapid shutdown" of ESS. It just requires a readily accessible disconnect. That would be the 30A breakers each Powerwall connects to. 705.23 doesn't require it to be outside, it just need to be accessible without the use of tools (other than keys), without navigating around obstacles, and without requiring portable ladders and the like.

All of California, and much of the US, has adopted the 2017 NEC. For a map, see https://nfpa.org/-/media/Images/NEC/Adoption-Maps/NECInEffect11120.ashx

Cheers, Wayne
 

holeydonut

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Jun 27, 2020
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East Bay NorCal
Keep in mind this is PG&E we're talking about. They are the ones that...

... took 2 months to confirm the underground service wire gauge and class of service already connected to my home
... bickered over whether a Main Service Panel was considered "generation equipment" for their Greenbook like-for-like
... thought there was some way my house could draw 200 A of power from the grid while simultaneously pushing 125 A of PV generation and battery energy to the grid
... have had employees tell me they don't like customers installing solar and resiliency since it takes money from them

I don't think I can win an argument with PG&E over "accessible" versus "readily accessible" versus "readily accessible outside". I'm still picturing some grumpy PG&E rep telling me they can't read the "ON" and "OFF" lettering on this Square D disconnect since it's not in highly reflective paint/tape.

I don't understand how any customer wins when PG&E is involved.
 
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Vines

Active Member
Jul 20, 2018
1,896
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Silicon Valley, CA
Keep in mind this is PG&E we're talking about. They are the ones that...

... took 2 months to confirm the underground service wire gauge and class of service already connected to my home
... bickered over whether a Main Service Panel was considered "generation equipment" for their Greenbook like-for-like
... thought there was some way my house could draw 200 A of power from the grid while simultaneously pushing 125 A of PV generation and battery energy to the grid
... have had employees tell me they don't like customers installing solar and resiliency since it takes money from them

I don't think I can win an argument with PG&E over "accessible" versus "readily accessible" versus "readily accessible outside". I'm still picturing some grumpy PG&E rep telling me they can't read the "ON" and "OFF" lettering on this Square D disconnect since it's not in highly reflective paint/tape.

I don't understand how any customer wins when PG&E is involved.

Those reasons are likely why some just throw a bladed lockable on the wall. Its perfectly fine to not take the exception and throw a disco on the wall in every case, just not desirable to have extra and ugly equipment that isn't as useful as it seems. Customers are really concerned with aesthetics in many cases.
 

Vines

Active Member
Jul 20, 2018
1,896
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Silicon Valley, CA
There is a thing called the six handed rule 2017 NEC 230.71 that says that shutdown should be no more than 6 individual switches. So for instance if you have 7 strings of SPR-A415-G-AC you should use a main breaker in the combiner panel where they all come together.
 
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