Main service panel upgrade

[jkim]

I have to two solar installers. One says I need a $2500 service panel upgrade (See below) and another says my service panel is fine and needs no upgrade. who to believe?


This is the email I got from the installers who says I need an upgrade You need a main panel upgrade because we can only feed a certain amount of solar in a main electrical panel; this rule is referred to as the 120% rule. This rule states that you can only "back-feed" 120% of the main bus bar rating with solar. So now, let me demonstrate this in plain English through some calculations. All calculations will be based off your current situation (a photo of your electrical panel is below):

To the set the stage, you have a 200 Amp-rated main electrical panel with NO main disconnect. In other words, you have 200 Amps being delivered from PG&E to your home and your main electrical panel has no main breaker (I.e. Main disconnect - a breaker to shut off ALL power to your home).

You have the following breakers:

Oven - 40 Amps
Car Charger - 30 Amps
Dryer- 30 Amps
A/C - 40 Amps
Existing Solar - 20 Amps
Sub Panel- 100 Amps

If you add all of these breaker ratings up, you will see that you have 260 Amps worth of main disconnects (every breaker is a main disconnect since you do not have a "main disconnect"). So, finally here is the calculation for solar companies to abide by:

120% of the main panel rating (I.e. Bus bar rating) - main disconnect(s) = the amount of solar you can install in your home.

Given your current situation, here is how many Amps you can install (from a code perspective) in your panel:

200 (bus bar rating) x 1.2 (120% rule) = 240 maximum amount of Amps - 260 (sum of all disconnects) = -20 Amps of solar. So, how can you install a negative number of amps? THAT'S CORRECT, YOU CAN'T!!!


So, now let's do this calculation if you had a panel with a main disconnect:

200 (bus bar rating) x 1.2 (120% rule) = 240 maximum amount of Amps - 200 (sum of all disconnects) = 40 Amps of solar. TADA, everything works.

The only difference in these two scenarios, is that in scenario 2 you have a "main disconnect." So, you don't think that I am full of hot air and pulling this rule out of the sky, I have attached a link that explains this in more detail: https://www.civicsolar.com/resource/120-rule-“what-it-and-why-it-important”-0

[sensij]

I guess one question is, how did the 20 A of existing solar get installed? It appears to already violate the 120% rule. Nothing the installer writes looks incorrect to me... not having a main supply breaker is unusual. You might want to check with the city yourself to make sure the interpretation of your system is correct.

[Mike90250]

You may find when the inspector comes out, HE may require a Main Disconnect be installed. Depends on your local code and his attiude

[foo1bar]

I guess one question is, how did the 20 A of existing solar get installed? It appears to already violate the 120% rule.

I agree.

Only way I see it being possible to keep that panel is if you can downsize the 100A that goes to the subpanel. But that's going to require some calculations to see how much it can be downsized (if it can)

Or maybe you can move the oven, dryer, AC and car charger to a subpanel - with a 100A breaker going to it. (Again would have to have an electrician do calculations to see if that's doable)
And then you'd be able to have another subpanel for the solar with 40A going to the solar subpanel - then 20A for existing solar and 20A for new solar.
(But IMO at that point you might as well have put in a new "main panel" that feeds this panel)


Really the Authority Having Jurisdiction (AHJ - ie. building inspector) is the final word on it - if they approved what you have now, its possible they'd approve increasing the solar breaker to 40A and having a subpanel for the solar.
I don't think they would approve it- but you can ask them.
I think most inspectors will be happy that a homeowner is asking "Do I need X" beforehand when they're getting conflicting info from contractors.
Then they don't have to give the homeowner the bad news later on.

It's also possible that the one not planning to do a new main panel is planning on a line-side tap.
(Depending on the location you're at the POCO and/or AHJ may or may not allow line-side taps)

Good luck.

[jkim]

I guess one question is, how did the 20 A of existing solar get installed? It appears to already violate the 120% rule. Nothing the installer writes looks incorrect to me... not having a main supply breaker is unusual. You might want to check with the city yourself to make sure the interpretation of your system is correct.

I already have solar panels with solarcity (I really hate solarcity)

And now need more solar panels. I reached out to two other installers and got two different answers.

[jkim]

I agree.

Only way I see it being possible to keep that panel is if you can downsize the 100A that goes to the subpanel. But that's going to require some calculations to see how much it can be downsized (if it can)

Or maybe you can move the oven, dryer, AC and car charger to a subpanel - with a 100A breaker going to it. (Again would have to have an electrician do calculations to see if that's doable)
And then you'd be able to have another subpanel for the solar with 40A going to the solar subpanel - then 20A for existing solar and 20A for new solar.
(But IMO at that point you might as well have put in a new "main panel" that feeds this panel)


Really the Authority Having Jurisdiction (AHJ - ie. building inspector) is the final word on it - if they approved what you have now, its possible they'd approve increasing the solar breaker to 40A and having a subpanel for the solar.
I don't think they would approve it- but you can ask them.
I think most inspectors will be happy that a homeowner is asking "Do I need X" beforehand when they're getting conflicting info from contractors.
Then they don't have to give the homeowner the bad news later on.

It's also possible that the one not planning to do a new main panel is planning on a line-side tap.
(Depending on the location you're at the POCO and/or AHJ may or may not allow line-side taps)

Good luck.

30 amp dryer outlet is actually the car charging outlet (for my volt)
30 amp car charger is NOT being used at all.

[foo1bar]

30 amp dryer outlet is actually the car charging outlet (for my volt)
30 amp car charger is NOT being used at all.

So if a 30A is removed (since it's not being used) then possibly you have headroom to change your current 20A solar breaker to a 30A breaker. (And you'd still need a subpanel for the solar that would have the 20A for the existing and a breaker for the new one)
You haven't said how big your new system is going to be - so that may or may not be a viable solution.

Messy.

My advice is to take a few hours and go talk to the AHJ.

[jkim]

So if a 30A is removed (since it's not being used) then possibly you have headroom to change your current 20A solar breaker to a 30A breaker. (And you'd still need a subpanel for the solar that would have the 20A for the existing and a breaker for the new one)
You haven't said how big your new system is going to be - so that may or may not be a viable solution.

Messy.

My advice is to take a few hours and go talk to the AHJ.

Who is AHJ?

My 2nd set of solar is small. 3.3kW system

[foo1bar]

Who is AHJ?

Authority
Having
Jurisdiction

aka building inspector in most places.

[ButchDeal]

I already have solar panels with solarcity (I really hate solarcity)

And now need more solar panels. I reached out to two other installers and got two different answers.

Is your existing contract with SolarCity a PPA? Or a lease or loan?

[J.P.M.]

I already have solar panels with solarcity (I really hate solarcity)

My condolences.

[inetdog]

Here is what should be the bottom line(s).
1. If you have at most six breakers in the main panel you do not need to have a main breaker. The six together form the service disconnect. They are allowed to add up to more than the service size with no limit.
2. The addition of a seventh breaker to the panel for the PV wouid be legal but not necessarily accepted, and it would be a line side tap. No 120% rule.
3. If the solar goes into a sub panel, then the sub will have to meet the 120% rule, but still no problem with the main, as long as the PV is less than the service size.