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'whole home backup' confusion

jgbaum

Member
Aug 25, 2021
23
11
San Diego
I recently had a system installed (16kW, 2PW+, backup gateway 2) and all of my paperwork references 'whole home backup'. Basically, they pulled all of my loads from my main panel into a subpanel connected to the gateway. The only breaker in my main panel now is a 100A going to the gateway. What's odd to me is that they had me upgrade my main panel and service (which required significant trenching and $$$) from 100A to 200A, but they're only feeding this subpanel (which is capable of 225A) with 100A. There are several new loads I'd like to add in the coming months (EV chargers, electric dryer, water heater), which my project advisor was aware of, but there doesn't seem to be the bandwidth to support these in the subpanel. Am I mistaken? Should I ask Tesla to update the wiring/breaker to 200A?

My understanding (which may be wrong!) is that in order to be powered by my PV system or PWs when the grid is out, loads would need to be in the subpanel as no electricity would flow to the main.

I've included the wiring diagram below. Any insight would be much appreciated.

Thanks!


n91ktoodr6i71.png
 

wwhitney

Active Member
Nov 2, 2017
1,117
1,482
Berkeley, CA
But for real, why would two grounding rods and two neutral to ground bonds within 2 feet of each other actually pose a problem?
Part of the neutral current for all your loads downstream of the TEG2 is possibly flowing through the case of the TEG2 (and the EGC between the TEG2 and the meter main, which if that is metal conduit is also exposed to touch). So in theory that exposed metal may be at an elevated voltage from ground, and it's possibly a shock hazard. It's certainly undesirable current and is prohibited by the NEC.

Cheers, Wayne
 
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holeydonut

Active Member
Supporting Member
Jun 27, 2020
2,642
1,986
East Bay NorCal
Part of the neutral current for all your loads downstream of the TEG2 is possibly flowing through the case of the TEG2 (and the EGC between the TEG2 and the meter main, which if that is metal conduit is also exposed to touch). So in theory that exposed metal may be at an elevated voltage from ground, and it's possibly a shock hazard. It's certainly undesirable current and is prohibited by the NEC.

Cheers, Wayne


You know it's funny, the Sunrun electrician that was at my house to install the new MSP, Gateway, and these fancy grounding rods actually told me that all grounding rods can have elevated voltage. And that getting shocked by them was unavoidable. And to be careful because you know, getting shocked is no good.

I know you all probably think I'm making up half the stuff I post here. But for real; I'm not. The electrician even went further to say animals sometimes get a little jolt when they go up against grounding rods.

I think wwhitney should offer his services for sale to watch a solar+ess installation go in. So he can boss the people around and make sure they install things correctly when they do stupid stuff that only he knows is stupid while it's happening.

PS, my grounding rods are exposed on the out-side of my stucco walls because my house is on a concrete slab and they didn't want to actually go through the slab to get to ground.
 
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holeydonut

Active Member
Supporting Member
Jun 27, 2020
2,642
1,986
East Bay NorCal
I recently had a system installed (16kW, 2PW+, backup gateway 2) and all of my paperwork references 'whole home backup'. Basically, they pulled all of my loads from my main panel into a subpanel connected to the gateway. The only breaker in my main panel now is a 100A going to the gateway. What's odd to me is that they had me upgrade my main panel and service (which required significant trenching and $$$) from 100A to 200A, but they're only feeding this subpanel (which is capable of 225A) with 100A. There are several new loads I'd like to add in the coming months (EV chargers, electric dryer, water heater), which my project advisor was aware of, but there doesn't seem to be the bandwidth to support these in the subpanel. Am I mistaken? Should I ask Tesla to update the wiring/breaker to 200A?

My understanding (which may be wrong!) is that in order to be powered by my PV system or PWs when the grid is out, loads would need to be in the subpanel as no electricity would flow to the main.

I've included the wiring diagram below. Any insight would be much appreciated.

Thanks!


n91ktoodr6i71.png


Lol I feel like your exact situation was experienced by another user like 2 months ago.

To answer your questions:

1) Yes, the box labeled [X] is the only one that will be powered if you cannot get energy from your power company

2) I feel like you got hit with the unfortunate situation others have had where your power company is forcing you to upgrade your main service panel to comply with whatever interpretation they have; but then Tesla realizes your home is configured in such a way that you only need 100A between your backed-up microgrid and the PG&E grid

3) If you add future loads into the main service panel, it is likely you would want some energy to be able to be exported from your batteries to be consumed by these upstream loads when the utility is operational. As all California utilities move to time of use rate plans, homeowners are incentivized to use their stored battery energy when possible between 4pm and 9pm (or 3pm and 11pm if you're on an EV rate plan).

When the time comes that you have a bunch of loads in the main service panel, you will likely want to have someone add Current Transducers (CT's) to allow your Tesla gateway to sense the upstream loads. With these sensors, you can configure the Tesla ESS system to export energy to feed these upstream loads if they are detected. But good luck finding someone to do this. I had a really rough time trying to set up a partial home backup because electricans/solar-folks/ESS-folks around me just refused to play ball.

And of course if the utility goes offline, the loads in the main service panel will be de-energized as well.
 
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wwhitney

Active Member
Nov 2, 2017
1,117
1,482
Berkeley, CA
PS, my grounding rods are exposed on the out-side of my stucco walls because my house is on a concrete slab and they didn't want to actually go through the slab to get to ground.
The NEC requires that a ground rod have 8' of length in contact with the earth. So when using 8' rod as is common, the top of the rod should be below grade, and the rod would not be exposed. If you have 10' rods, then you can leave some of the rod exposed, but there's no real upside, to my knowledge.

I don't know if you can determine the length after driving, even if the end was marked the driving process would probably mess it up. I don't have any direct experience with this, as I've only dealt with houses with new foundations that have CEEs, so they have no need for ground rods.

Cheers, Wayne
 
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BGbreeder

Member
Jun 19, 2020
562
357
Bay Area
You know it's funny, the Sunrun electrician that was at my house to install the new MSP, Gateway, and these fancy grounding rods actually told me that all grounding rods can have elevated voltage. And that getting shocked by them was unavoidable. And to be careful because you know, getting shocked is no good.
I struggle to think of a case where a correctly wired home system would shock you at a ground rod. @Vines @wwhitney comments?

"CEEs" = Concrete Encased Electrodes, aka Ufer grounds, i.e. grounding via rebar/conductor(s) in a foundation. More here. For a variety of reasons, including moisture content of soils, salts in the concrete, and a large surface area, Ufer showed that CEEs provide better and more reliable grounds than ground rods.

I agree the @wwhitney has a promising side business as an overseer of installations.

FWIW: Our solar ground rod, CEE, plumbing, and a MSP ground rod are all tied together at the MSP ground, where it is bonded to the neutral. I find grounding to be an interesting subject, and as the frequency and voltage change, different solutions may be optimal.

All the best,

BG
 
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holeydonut

Active Member
Supporting Member
Jun 27, 2020
2,642
1,986
East Bay NorCal
I struggle to think of a case where a correctly wired home system would shock you at a ground rod. @Vines @wwhitney comments?

"CEEs" = Concrete Encased Electrodes, aka Ufer grounds, i.e. grounding via rebar/conductor(s) in a foundation. More here. For a variety of reasons, including moisture content of soils, salts in the concrete, and a large surface area, Ufer showed that CEEs provide better and more reliable grounds than ground rods.

I agree the @wwhitney has a promising side business as an overseer of installations.

FWIW: Our solar ground rod, CEE, plumbing, and a MSP ground rod are all tied together at the MSP ground, where it is bonded to the neutral. I find grounding to be an interesting subject, and as the frequency and voltage change, different solutions may be optimal.

All the best,

BG


I think the good designers and installers work for wherever Vines works instead of working for Sunrun hah.

BTW, did they bond all of your ground stuffs to your gas riser as well? Of my two ground rods, one is clamped to the home-side of the gas riser (the house-side of the gas meter). From the clamp, there's copper going to a clamp that is affixed to the ground rod that is sticking up from the soil/grade about 5 inches.

Part of me is like... wtf why would you want to direct electricity to the one thing that PG&E keeps thinking will explode? But then I'm thinking all this is a load of BS since my disconnects will protect me.
 
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wwhitney

Active Member
Nov 2, 2017
1,117
1,482
Berkeley, CA
Of my two ground rods, one is clamped to the home-side of the gas riser (the house-side of the gas meter). From the clamp, there's copper going to a clamp that is affixed to the ground rod that is sticking up from the soil/grade about 5 inches.
The interior metal gas piping should be bonded to the grounding system, e.g. as you've described. The meter has a dielectric union, so the utility side gas piping is not electrically continuous with the house side gas piping.

Cheers, Wayne
 
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miimura

Well-Known Member
Aug 21, 2013
6,852
6,740
Los Altos, CA
Since I was watching just about everything while my house was being built, I know that both of my service lines are plastic. Both gas and water. Expecting such service piping to be useful as a ground is amusing to me. Of course, the gas pipes on the house side of the meter are all iron, so they do need to be grounded somewhere. The most amusing thing to me was the guy who had the job of welding my gas service stub to the underground distribution pipe while it was actively venting gas.
 
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BGbreeder

Member
Jun 19, 2020
562
357
Bay Area
I think the good designers and installers work for wherever Vines works instead of working for Sunrun hah.

BTW, did they bond all of your ground stuffs to your gas riser as well? Of my two ground rods, one is clamped to the home-side of the gas riser (the house-side of the gas meter). From the clamp, there's copper going to a clamp that is affixed to the ground rod that is sticking up from the soil/grade about 5 inches.

Part of me is like... wtf why would you want to direct electricity to the one thing that PG&E keeps thinking will explode? But then I'm thinking all this is a load of BS since my disconnects will protect me.
Yes, as NEC requires and @wwhitney points out, there is a dielectric union on the gas entry, and to be complete, yes, bonds across the hot water heater to the gas, just in case. I believe that the latter are targeting at grounding any potential home AC from getting into water.

And to complete the belt and suspenders, there is a whole house surge protector in the main service panel, connected to the same ground MSP and solar ground rods and grounding system.

I do wonder about ground loops in the soil with respect to grounding sub-panels, but I am not an expert. There is already a soil ground loop from the transformer ground to the house grounds. Would grounding and bonding neutral to ground (and ground rods) in sub-panels make it worse? Would that help clamp EMP transients from lightning strikes? Semiconductors aren't very tolerant of voltage transients.

Isn't there a requirement for the tops of lightning ground rods to be buried? (So as not to create sharp electric fields off of the edges?)

All the best,

BG
 
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holeydonut

Active Member
Supporting Member
Jun 27, 2020
2,642
1,986
East Bay NorCal
Isn't there a requirement for the tops of lightning ground rods to be buried? (So as not to create sharp electric fields off of the edges?)



County inspector actually thought the ground rods were too close to the gas riser (Sunrun had put both within 6 inches of the riser) and asked them to relocate about 12 inches away. He didn't say anything about the ends sticking up.

I still don't understand how a MSP located within 36" from a gas riser = 🔥
But funneling a potential lightning strike down within a foot of the same gas riser = 👍

And no weep holes = 😿
 
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BGbreeder

Member
Jun 19, 2020
562
357
Bay Area
County inspector actually thought the ground rods were too close to the gas riser (Sunrun had put both within 6 inches of the riser) and asked them to relocate about 12 inches away. He didn't say anything about the ends sticking up.

I still don't understand how a MSP located within 36" from a gas riser = 🔥
But funneling a potential lightning strike down within a foot of the same gas riser = 👍

And no weep holes = 😿

Code rules are written by committees of experts, with inputs from others, but at the end of the day, human beings. Generally, the code rules have made homes safer; less likely to fall down, electrocute you, gas you with sewer vapors, or give you typhoid. But that doesn't mean perfect, nor does it mean logical.

And those ground rods are really there to ground stray voltages generated in your system. If you want lighting system, it is a whole different ball game. That 4ga, or whatever you have doesn't cut it for lightning, which is more more on the order of 1/2" or more in diameter, with much more elaborate grounding systems in many soils. Fortunately, lightning strikes are pretty rare in California, relatively speaking, the 2020 lightning blitz notwithstanding.

All the best,

BG
 
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ptdusn

Member
Nov 10, 2021
74
24
Gilbert, AZ
Code rules are written by committees of experts, with inputs from others, but at the end of the day, human beings. Generally, the code rules have made homes safer; less likely to fall down, electrocute you, gas you with sewer vapors, or give you typhoid. But that doesn't mean perfect, nor does it mean logical.

And those ground rods are really there to ground stray voltages generated in your system. If you want lighting system, it is a whole different ball game. That 4ga, or whatever you have doesn't cut it for lightning, which is more more on the order of 1/2" or more in diameter, with much more elaborate grounding systems in many soils. Fortunately, lightning strikes are pretty rare in California, relatively speaking, the 2020 lightning blitz notwithstanding.

All the best,

BG
I wholly agree @BGbreeder, when I worked on high powered (40kW and 85K plate voltage) transmitters in the Navy, they had a lot of grounding straps all over the place to alleviate stray voltages.
 
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