Moving PV connection to subpanel

[944pv]

I have a metered main service panel with no main breaker (125A bus), a 7.6kw inverter is hooked up to the system as a Supply side connection with a 60A breaker.
All the slots are taken in the MSP : A 90A breaker that feeds a subpanel and a 60A breaker to the inverter. The 120% rule doesn't apply because there is no main breaker.

I'm converting my gas water heater to electric, and it is pushing the 90A limit at the subpanel. I don't want to upgrade the MSP because it takes power shut off request with the utility company and stucco work, so I want to install a new subpanel for the new water heater and future EV charger.

Questions:
1. What is the max size breaker I can use for the new subpanel?
2. The PV inverter will need to hook up at the new subpanel, because the MSP is out of room. Is that ok?
3. Should the subpanel have a main breaker? If so, what size?

 

[jaggedben]

If this is DIY then this thread will likely be closed.

Question 1: technically it can be anything but really depends on doing load calculations. If the 125A service is not adequate for the existing load plus water heater and EV charger then adding a subpanel does not solve that. Load calculations are at the center of your question here.

Question 2: yes it's okay to relocate the PV to a subpanel as long as 120% rule or another applicable rule is followed at the sub.

Question 3: I see no reason a new subpanel would need a main breaker. It would be protected by a breaker in the meter main.

 

[ggunn]

Question 2: yes it's okay to relocate the PV to a subpanel as long as 120% rule or another applicable rule is followed at the sub.

And in the main panel as well, of course.

 

[jaggedben]

And in the main panel as well, of course.

But there's no load side bus in the meter main.

 

[jaggedben]

(Also a 7.6kW inverter doesn't need to be on a 60A breaker, typically.)

 

[944pv]

The house has 100A service.
The bus is protected by the only 90A load breaker now.
Suppose the new subpanel is fed by a 2nd 90A breaker, and both subpanel exceeds 125A load, what's going to give?
There is no main breaker, so the bus melts?

 

[944pv]

You're right, the 7.6kw inverter has a 40A breaker, not 60A.

 

[ggunn]

But there's no load side bus in the meter main.

Ah, right. No main breaker.

 

[wwhitney]

The 90A breaker could be upsized to 125A (the bus rating) to provide for additional load capacity, without changing the solar side of things, at least as far as article 705 goes, right? Maybe someone mistakenly thought the 120% rule applied to the service conductor bus on this MLO service panel (90A + 60A = 1.2 * 125A).

Although if this is in CA as per the zip code, since CA is on the 2020 NEC now, can any changes be made to the MLO service panel, over than converting it to a single breaker panel? In which case a single 125A breaker in the service panel could supply a 125A feeder to a new 200A bus panel for a PV breaker and breaker(s) for the load panel(s). Or to a 125A feeder to a 125A main breaker load panel, with the PV using a feeder interconnection.

Cheers, Wayne

 

[944pv]

Every house in the neighborhood has 90A to the subpanel in the garage.
I think the builder spec'ed the aluminum wire to 90A between MSP and the old subpanel.

 

[jaggedben]

The house has 100A service.

How do you know?

The bus is protected by the only 90A load breaker now.
Suppose the new subpanel is fed by a 2nd 90A breaker, and both subpanel exceeds 125A load, what's going to give?
There is no main breaker, so the bus melts?

Believe it or not the code allows this situation as long as the calculated load is less than the service rating. Although I've certainly met some inspectors who didn't know that.

See 230.90 Exception 3.

Load calcs, load calcs, load calcs...

 

[jaggedben]

...

Although if this is in CA as per the zip code, since CA is on the 2020 NEC now, can any changes be made to the MLO service panel, over than converting it to a single breaker panel? ...

It's a valid question, since it's anybody's guess how AHJs will decide to deal with existing panels like this.

 

[Rodsic]

Hello all!

A follow-up question. What if I am trying to land the PV breaker in a subpanel that has no main breaker and no feeder breaker, and is instead fed by lugs in the main panel? Does the subpanel require a main/feeder breaker? Or can I simply use the main breaker in the main panel for available backfeed calculations (using 120% rule)?

Thanks!

 

[ggunn]

Hello all!

A follow-up question. What if I am trying to land the PV breaker in a subpanel that has no main breaker and no feeder breaker, and is instead fed by lugs in the main panel? Does the subpanel require a main/feeder breaker? Or can I simply use the main breaker in the main panel for available backfeed calculations (using 120% rule)?

Thanks!

Yes; in a subpanel there is no difference between a main breaker in a subpanel and a breaker in the main panel feeding a MLO sub. Of course, you still have to contend with 705 in the main panel.