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How to Connect Solar To Electrical. First inspection failed…

3L3CTRIC

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I currently have a solar system installed, but it failed the inspection because the engineer did not have the electrical system listed properly. After confirming the system with the engineer, I’m having issues confirming the correct way to connect it to the house.

Here is the current electrical setup.

- Main Service Panel - 200A Main
- Main Service Panel - 225A Busbar

- Feeder Wires - 2/0 CU (Connects Main Panel to Sub Panel)

- Sub Panel - No Main (it gets fed from the 200A Main Service)
- Sub Panel - 225A Busbar

Now that we’ve established that, we’re having issues confirming WHERE the solar needs to be installed in the system.

1. Option 1 - Main Breaker (200A) > Solar Breaker (70A) > 2/0 CU Feeder Wires > Sub Panel (Loads)

2. Option 2 - Main Breaker (200A) > 2/0 CU Feeder Wires > Sub Panel (Loads) > Solar Breaker (70A)

To confirm, the Main Panel and Sub Panel Busbar ratings are both 225Amps. I thought the 70A Solar needed to be added at the furthest distance away from the Main (Option 2)…but the Engineer confirmed it could be installed in the Main (Option 1).

Which is the correct way to install?
 
I currently have a solar system installed, but it failed the inspection because the engineer did not have the electrical system listed properly. After confirming the system with the engineer, I’m having issues confirming the correct way to connect it to the house.

Here is the current electrical setup.

- Main Service Panel - 200A Main
- Main Service Panel - 225A Busbar

- Feeder Wires - 2/0 CU (Connects Main Panel to Sub Panel)

- Sub Panel - No Main (it gets fed from the 200A Main Service)
- Sub Panel - 225A Busbar

Now that we’ve established that, we’re having issues confirming WHERE the solar needs to be installed in the system.

1. Option 1 - Main Breaker (200A) > Solar Breaker (70A) > 2/0 CU Feeder Wires > Sub Panel (Loads)

2. Option 2 - Main Breaker (200A) > 2/0 CU Feeder Wires > Sub Panel (Loads) > Solar Breaker (70A)

To confirm, the Main Panel and Sub Panel Busbar ratings are both 225Amps. I thought the 70A Solar needed to be added at the furthest distance away from the Main (Option 2)…but the Engineer confirmed it could be installed in the Main (Option 1).

Which is the correct way to install?

Not enough info.

Is this grid-tie or what?
 
To confirm, the Main Panel and Sub Panel Busbar ratings are both 225Amps. I thought the 70A Solar needed to be added at the furthest distance away from the Main (Option 2)…but the Engineer confirmed it could be installed in the Main (Option 1).
Based on the assumption that you're in the United States that used to be how solar was often interconnected. Now they don't accept that in many places I believe. My memory is that you'd have to be on a pretty old code or have no inspector for that to be acceptable nowadays.

Just a guess but to me it sounds like you're violating the 120% rule but admittedly I can't clearly see the entire picture. Did the inspector mention that?

225A x 1.2 - 225A = 55A max solar breaker

If that's what going on I believe your solutions are is to either downsize the main breaker to 175 amps or to do a line side tap upstream of your current main breaker or busbar.

225A x 1.2 - 175A = 95A max solar breaker. Some (many?) houses can even get away with a 150 main breaker and they are normally cheaper.
 
Based on the assumption that you're in the United States that used to be how solar was often interconnected. Now they don't accept that in many places I believe. My memory is that you'd have to be on a pretty old code or have no inspector for that to be acceptable nowadays.

Just a guess but to me it sounds like you're violating the 120% rule but admittedly I can't clearly see the entire picture. Did the inspector mention that?

225A x 1.2 - 225A = 55A max solar breaker

If that's what going on I believe your solutions are is to either downsize the main breaker to 175 amps or to do a line side tap upstream of your current main breaker or busbar.

225A x 1.2 - 175A = 95A max solar breaker. Some (many?) houses can even get away with a 150 main breaker and they are normally cheaper.
My main breaker is 200…the busbar is rated for 225A.

So wouldn’t your calculation be 225A x 1.2 - 200A = 70A Max Solar breaker?

We’re doing 70A, I’m just wondering how they should connect it. In the main before all my loads…or in the sub panel after the loads (furthest away from my main breaker).

Not enough info.

Is this grid-tie or what?
US install. Feeding power back to my utility. Not sure if that helps clarify.
 
My main breaker is 200…the busbar is rated for 225A.

So wouldn’t your calculation be 225A x 1.2 - 200A = 70A Max Solar breaker?

We’re doing 70A, I’m just wondering how they should connect it. In the main before all my loads…or in the sub panel after the loads (furthest away from my main breaker).


US install. Feeding power back to my utility. Not sure if that helps clarify.

You connect it the same way you would do a 4 wire 240V circuit.

Each leg to each side of the breaker, then ecg and neutral to bar. If that's what you mean?

Nothing special. No hold down needed or anything like that.

Edit: sorry, I missed the in main or sub panel. I thought you had already decided to do it in main panel based on your first post where the engineer said that was now OK.

Either way I'm lost. Are you asking if you should put the solar breaker in the sub or main panel? Since the capacity is the same in either case (you stated 70 amp breaker in both cases), do whichever one is easier.
 
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My main breaker is 200…the busbar is rated for 225A.

So wouldn’t your calculation be 225A x 1.2 - 200A = 70A Max Solar breaker?

We’re doing 70A, I’m just wondering how they should connect it. In the main before all my loads…or in the sub panel after the loads (furthest away from my main breaker).
Correct, I was using the more conservative calculation not seeing clearly seeing your situation.

My very limited understanding is that the key point of the 120% rule is allow you to put the solar input breaker anywhere (or moved in the future) since the additive amps of the solar input and the main breaker are within the safe limits of the busbar. Still, best practice would be to put the solar input breaker opposite the main. I believe it's Kirchhoff's Law that tells us that but I'm still on my first cup of coffee.

Regardless, why did the inspector fail you?
 
You connect it the same way you would do a 4 wire 240V circuit.

Each leg to each side of the breaker, then ecg and neutral to bar. If that's what you mean?

Nothing special. No hold down needed or anything like that.

Edit: sorry, I missed the in main or sub panel. I thought you had already decided to do it in main panel based on your first post where the engineer said that was now OK.

Either way I'm lost. Are you asking if you should put the solar breaker in the sub or main panel? Since the capacity is the same in either case (you stated 70 amp breaker in both cases), do whichever one is easier.
Hopefully this helps.

Here is my main panel. It has a 200A Main Breaker, 225A rated Busbar, and one breaker connected for an outdoor outlet.
38B35C13-938B-4A93-A213-955E3729E068.jpeg2BBF73CE-C2B9-4A09-8D6D-66A302EAAD58.jpeg

From there, the feeder wires (2/0 CU) connect to the sub panel where all of my breakers are. There is no main breaker in my sub panel (it gets fed from the main service outside) and the busbar is rated for 225A.

C070E166-D289-4827-B31F-FE0EF6F3D6A7.jpeg3A83D56A-6379-47F0-B319-6997CBD1DE3B.png

They originally wanted to tap into the feeder wires, which is why it failed the first inspection. Now we’re trying to decide WHERE to land this 70A breaker for the solar.

Is it in the main service (outside)? Or in the sub panel (inside) at the top where the empty breaker slots are which is the furthest distance from my main breaker?

I’m hearing conflicting info about the 120% rule and where it needs to land.

Correct, I was using the more conservative calculation not seeing clearly seeing your situation.

My very limited understanding is that the key point of the 120% rule is allow you to put the solar input breaker anywhere (or moved in the future) since the additive amps of the solar input and the main breaker are within the safe limits of the busbar. Still, best practice would be to put the solar input breaker opposite the main. I believe it's Kirchhoff's Law that tells us that but I'm still on my first cup of coffee.

Regardless, why did the inspector fail you?

See my response above to see if this helps with my install.
 
You'd normally put the solar breaker at the opposite end from the feed into the panel. This is done so that the bus bars can't be overloaded in one specific point.

That doesn't work in your main panel because your pulling the sub panel straight out the bottom. So the portion between the bottom breaker slot and those lugs has to carry all 275 amps (in case of a fault)

What does the sub panel look like inside?
Edit: I read your post more thorough. The sub panel feeds in the bottom. I'd put the PV breaker at the top of the sub panel.

I don't see circuit protection on either end of the 2/0 between the panels. 2/0 is rated at 195 amps (best case) before any derating. I'm surprised that was approved.
Edit: If you put the PV anywhere in the main panel you could have 270 amps on this 2/0 wire
 
Hopefully this helps.

Here is my main panel. It has a 200A Main Breaker, 225A rated Busbar, and one breaker connected for an outdoor outlet.
View attachment 119202View attachment 119203

From there, the feeder wires (2/0 CU) connect to the sub panel where all of my breakers are. There is no main breaker in my sub panel (it gets fed from the main service outside) and the busbar is rated for 225A.

View attachment 119204View attachment 119205

They originally wanted to tap into the feeder wires, which is why it failed the first inspection. Now we’re trying to decide WHERE to land this 70A breaker for the solar.

Is it in the main service (outside)? Or in the sub panel (inside) at the top where the empty breaker slots are which is the furthest distance from my main breaker?

I’m hearing conflicting info about the 120% rule and where it needs to land.



See my response above to see if this helps with my install.

Edit: Place it in the outside (main panel)
 
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What you're calling the main panel is what I would normally call a meter combo panel with pass through lugs. Your "main panel" is inside in the garage and I'm guessing directly behind the meter combo outside since it doesn't have a main breaker.

In essence you have one busbar fed by the 200 amp breaker outside.

What's odd to me is that you don't appear to be violating the 120% rule so I'm sticking with my original response which is place the solar input breaker on the opposite end of the busbar from main breaker. That would be the top of main panel (inside panel).
 
I currently have a solar system installed, but it failed the inspection because the engineer did not have the electrical system listed properly. After confirming the system with the engineer, I’m having issues confirming the correct way to connect it to the house.

Here is the current electrical setup.

- Main Service Panel - 200A Main
- Main Service Panel - 225A Busbar

- Feeder Wires - 2/0 CU (Connects Main Panel to Sub Panel)

- Sub Panel - No Main (it gets fed from the 200A Main Service)
- Sub Panel - 225A Busbar

Now that we’ve established that, we’re having issues confirming WHERE the solar needs to be installed in the system.

1. Option 1 - Main Breaker (200A) > Solar Breaker (70A) > 2/0 CU Feeder Wires > Sub Panel (Loads)

2. Option 2 - Main Breaker (200A) > 2/0 CU Feeder Wires > Sub Panel (Loads) > Solar Breaker (70A)

To confirm, the Main Panel and Sub Panel Busbar ratings are both 225Amps. I thought the 70A Solar needed to be added at the furthest distance away from the Main (Option 2)…but the Engineer confirmed it could be installed in the Main (Option 1).

Which is the correct way to install?

Good catch!
 
Why can't he put it in the main (outside) panel?
Because the 70 amps of the solar input breaker will add to the 200 amps of the main breaker. EG: before solar the main would trip when 200 amps was exceeded but after solar it will take 270 amps before the main breaker trip.

Edit: but then I'm not sure how to look at the 2/0 wire connecting the two which may be the problem?? It shouldn't be in there to begin with because it only rated at 175 amps (you have to use the 75c row on Table 310.15 for residential). He'd have to to step up to 4/0 to get to 230 amps to match the busbars and still pas the 120% rule but that's just a theory.
 
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Because the 70 amps of the solar input breaker will add to the 200 amps of the main breaker. EG: before solar the main would trip when 200 amps was exceeded but after solar it will take 270 amps before the main breaker trip.

The main breaker is between the meter and main panel busbars though.

The main and sub both have same 225 amp busbar rating.

Others more observant than I noticed the ampacity of the wires connecting the main and subpanel is 195 amps which is the limiting factor for installing in that panel vs the Sub.

Very good!
 
You'd normally put the solar breaker at the opposite end from the feed into the panel. This is done so that the bus bars can't be overloaded in one specific point.

That doesn't work in your main panel because your pulling the sub panel straight out the bottom. So the portion between the bottom breaker slot and those lugs has to carry all 275 amps (in case of a fault)

What does the sub panel look like inside?
Edit: I read your post more thorough. The sub panel feeds in the bottom. I'd put the PV breaker at the top of the sub panel.

I don't see circuit protection on either end of the 2/0 between the panels. 2/0 is rated at 195 amps (best case) before any derating. I'm surprised that was approved.
Edit: If you put the PV anywhere in the main panel you could have 270 amps on this 2/0 wire
Thanks.

So…I need to land the solar in the inside panel at the top where those empty breaker slots are? That would be the furthest distance away from the main breaker (and all the other loads would be in between the main breaker and solar breaker).

Would I need to upgrade that 2/0 CU wire? Or would that be fine to leave as is?

What you're calling the main panel is what I would normally call a meter combo panel with pass through lugs. Your "main panel" is inside in the garage and I'm guessing directly behind the meter combo outside since it doesn't have a main breaker.

In essence you have one busbar fed by the 200 amp breaker outside.

What's odd to me is that you don't appear to be violating the 120% rule so I'm sticking with my original response which is place the solar input breaker on the opposite end of the busbar from main breaker. That would be the top of main panel (inside panel).
Thanks for your feedback. And what about the 2/0 CU wire?

Because the 70 amps of the solar input breaker will add to the 200 amps of the main breaker. EG: before solar the main would trip when 200 amps was exceeded but after solar it will take 270 amps before the main breaker trip.

Edit: but then I'm not sure how to look at the 2/0 wire connecting the two which may be the problem?? It shouldn't be in there to begin with because it only rated at 175 amps (you have to use the 75c row on Table 310.15 for residential). He'd have to to step up to 4/0 to get to 230 amps to match the busbars and still pas the 120% rule but that's just a theory.
Interesting…so 2/0 CU isn’t rated properly for what I have without the solar? I find that hard to believe as this was new construction and went through a strenuous approval process.

I have to imagine upgrading those feeders aren’t that difficult (it’s only a 2ft run) as the main goes back to back with the sub panel.
 
Interesting…so 2/0 CU isn’t rated properly for what I have without the solar? I find that hard to believe as this was new construction and went through a strenuous approval process.
That's right, but I do mostly specialty commercial and light industrial, no residential wiring or much of of any work that involves inspections or permits for that matter.

I don't have an answer other than to offer I've it seen before on new resi construction and it's passed from day one somehow. It's more than I can succinctly get into at the moment (or ever lol) but for residential you're limited to the 75c chart because that's the highest rated breaker lug temp rating they make. I don't' think you'll find a residential breaker rated higher than 75c.

Below is straight from SquareD.

The wire temperature rating allowed for use in circuit breakers lugs is 75°C. While it is acceptable to use 90°C wire, that 90°C wire must be sized as if it is 75°C wire. This is according to the UL standard for circuit breakers, which is summarized as follows:
(1) Breakers rated 125 A or less must be marked for use with 60°C, 60/75°C, or 75°C only wire.
(2) For breakers rated more than 125 A, the proper wire temperature rating is 75°C and the marking is optional.
(3) Wire with a higher temperature rating can be used (e.g. 90°C), but the ampacity of the wire must be based on the wire temperature marked on the breaker.

Therefore, as marked on the breaker, the wire must be sized as 75°C wire. Even when using 90°C wire, the wire must be sized as if it is 75°C wire.


1667668387646.png
 
That's right, but I do mostly specialty commercial and light industrial, no residential wiring or much of of any work that involves inspections or permits for that matter.

I don't have an answer other than to offer I've it seen before on new resi construction and it's passed from day one somehow. It's more than I can succinctly get into at the moment (or ever lol) but for residential you're limited to the 75c chart because that's the highest rated breaker lug temp rating they make. I don't' think you'll find a residential breaker rated higher than 75c.

Below is straight from SquareD.

The wire temperature rating allowed for use in circuit breakers lugs is 75°C. While it is acceptable to use 90°C wire, that 90°C wire must be sized as if it is 75°C wire. This is according to the UL standard for circuit breakers, which is summarized as follows:
(1) Breakers rated 125 A or less must be marked for use with 60°C, 60/75°C, or 75°C only wire.
(2) For breakers rated more than 125 A, the proper wire temperature rating is 75°C and the marking is optional.
(3) Wire with a higher temperature rating can be used (e.g. 90°C), but the ampacity of the wire must be based on the wire temperature marked on the breaker.

Therefore, as marked on the breaker, the wire must be sized as 75°C wire. Even when using 90°C wire, the wire must be sized as if it is 75°C wire.


View attachment 119214
Should I ask my builder to update to 4/0 wire? Or could I pay an electrician to do so?

It’s literally a 2 ft run…so it would be very easy to upgrade.
 
Therefore, as marked on the breaker, the wire must be sized as 75°C wire. Even when using 90°C wire, the wire must be sized as if it is 75°C wire.
I don't think the 2/0 lands on a breaker at either end. It's in lugs in the main panel (per the pictures) and I believe it's in lugs in the "sub" panel (per the OP's description)

Would I need to upgrade that 2/0 CU wire? Or would that be fine to leave as is?
I'd upgrade it, but I think your engineer should be able to calculate the details. Or we can leave it to smarter individuals here.
Given the options, my preference would be 4/0 if the lugs at each end are large enough.
I have to imagine upgrading those feeders aren’t that difficult (it’s only a 2ft run) as the main goes back to back with the sub panel.
Probably very easy. I'm sure they'll spend significantly longer picking up the wire and driving to the work site.
 
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