Do I need to upgrade my main service panel?

[bsjaffa]

I have been meeting with solar system installers to install a grid-tied system at my house. Before I commit I want to verify whether I need to upgrade my main service panel. I have been reading about the 120% rule and am not sure if my current main service panel is sufficient. Any assistance would be greatly appreciated.

I will be getting a 9.28 kW system with a SolarEdge SE7600H-US Inverter (the model with an EV charger). I built my home 6 years ago and looking at my city permit paid for a 200 Amp service from the utility company. I believe my main service panel has a 150 A main service breaker that feeds my subpanel in my basement along with the majority of my breakers installed there. There are a few extra breakers installed in my main service panel. The labeling on my main service panel states "Mains 250 A max". Attached are pictures of my main service panel with the cover off and the label information.

My understanding is that the formula goes Busbar Rating * 120% - Main Service Breaker = Max Size of Inverter Breaker. So in my case does the label "Mains 250 A max" equal the Busbar rating so would my equation be 250 A * 120% - 150 A = 150 A? Which would be plenty big for a 40 A breaker for my system?

Also, would the new 40 A breaker for the inverter be installed in the top two spots, or the two spots below that are connected to the busbar?

https://ibb.co/D555F7X

https://ibb.co/DCL5rKM

[foo1bar]

My understanding is that the formula goes Busbar Rating * 120% - Main Service Breaker = Max Size of Inverter Breaker.

You don't have a end-feed busbar, so 120% rule doesn't apply to you.

It looks like you have a dedicated spot that can be used for solar, with a 50A max. So you can put in a 40A breaker there without problem.

[bsjaffa]

foo1bar thank you for confirming this!

[khanh dam]

You don't have a end-feed busbar, so 120% rule doesn't apply to you.

I have never seen a box like this with a "dedicated solar" circuit breaker spot. How is this dedicated spot wired to the rest of the panel? Why does it negate the 120% rule?
My logic would of been 250A is the actual maximum so 250a-150A = 100A of solar breakers could be installed which is about a 15-18kw system, more than most homes need.

[Ampster]

If I understand the wiring diagram in the attachments the top breaker spot connects to the line side at the meter and not to the buss bar.

[foo1bar]

I have never seen a box like this with a "dedicated solar" circuit breaker spot. How is this dedicated spot wired to the rest of the panel? Why does it negate the 120% rule?

The dedicated spot doesn't negate the 120% rule.
But that it is a center-fed panel would negate it if you're under 2014 NEC.
But I looked it up, and apparently under 2017 NEC that changed.
(705.12(D)(2)(3)(e)) the 120% rule can be applied to center-fed busbars as well - but only one side or the other, not both.

But I wouldn't bother with that approach because you already have a nice dedicated spot for solar on this.

My logic would of been 250A is the actual maximum so 250a-150A = 100A of solar breakers could be installed which is about a 15-18kw system, more than most homes need.

I don't know how you came to 250A - maybe by the same "Mains 250A max" the OP stated was on the label?
I think the 250A max is actually the sum of the 200A main (and probably 200A busbar) and the 50A dedicated spot. So I don't think it's a 250A busbar for the breakers.
But I am not a licensed electrician - just looking at what the OP posted in his pictures and stating how I'd interpret it.

For the OP, since there's this nice dedicated spot for a solar breaker with a 50A max, I would expect that's what the installer will use. (since he's installing a system that will need a 40A breaker, it fits in the 50A max spot with no problem)

[khanh dam]

well I learned something today, never knew this kind of dedicated solar circuit breaker box exsisted!

[NEOH]

The dedicated spot doesn't negate the 120% rule.
But that it is a center-fed panel would negate it if you're under 2014 NEC.
But I looked it up, and apparently under 2017 NEC that changed.
(705.12(D)(2)(3)(e)) the 120% rule can be applied to center-fed busbars as well - but only one side or the other, not both.

But I wouldn't bother with that approach because you already have a nice dedicated spot for solar on this.


I don't know how you came to 250A - maybe by the same "Mains 250A max" the OP stated was on the label?
I think the 250A max is actually the sum of the 200A main (and probably 200A busbar) and the 50A dedicated spot. So I don't think it's a 250A busbar for the breakers.
But I am not a licensed electrician - just looking at what the OP posted in his pictures and stating how I'd interpret it.

For the OP, since there's this nice dedicated spot for a solar breaker with a 50A max, I would expect that's what the installer will use. (since he's installing a system that will need a 40A breaker, it fits in the 50A max spot with no problem)

That Dedicated Spot does negate the 120% "Load-Side" rule.
Because that Dedicated Spot is on the Line-Side, with the Meter !
On the Line-Side, the PV Amps must now flow through the Main Breaker just like Grid amps to get to the Bus Bar.
With a Line-Side Tap, the PV amps cannot ever overload the bus bar - only a Load-Side PV Breaker can cause a Bus Bar overload.
With a Line-Side Tap, the Main Breaker perfectly protects the bus bar from overload as normal, regardless of the PV amps.
Therefore, "Line-Side Tap" NEC rules apply for that Special Spot.

[foo1bar]

That Dedicated Spot does negate the 120% "Load-Side" rule.

I would not call the below negating the rule. I'd say it's not applicable to the dedicated spot.

Because that Dedicated Spot is on the Line-Side, with the Meter !
On the Line-Side, the PV Amps must now flow through the Main Breaker just like Grid amps to get to the Bus Bar.
With a Line-Side Tap, the PV amps cannot ever overload the bus bar - only a Load-Side PV Breaker can cause a Bus Bar overload.
With a Line-Side Tap, the Main Breaker perfectly protects the bus bar from overload as normal, regardless of the PV amps.
Therefore, "Line-Side Tap" NEC rules apply for that Special Spot.

I think you don't even look at the line-side tap rules. You just look at the equipment instructions which say it's a dedicated spot with a 50A max.

I think we are in agreement that the dedicated spot has a 50A max, and the 120% rule has no bearing on that dedicated spot, which is not attached to the bus bar after the main breaker.

The 120% rule may or may not apply to the bus bar fed by the main breaker, as that is a center-fed bus bar. (2014 says 120% not allowed, but 2017 says 120% would be allowed)
But since there's the dedicated 50A spot, and the OP's plan is to do 40A breaker, the installer will presumably take advantage of that dedicated spot and there isn't any real need to look beyond that.

[bsjaffa]

Will we need to schedule with the utility company to turn off the power to our house in order to install the 40A breaker into that dedicated spot that?

[Ampster]

No, your contractor should be able to do that.