Updating panel

[HabitatSteve]

The panel in question is in CA. Old solar installed and has 125amp panel with label, presumably by solar installer before my daughter purchased home, saying it is downgraded to 100amp. I have spent the last years mostly on Habitat for Humanity homes and have no experience on solar, therefore the uneducated questions. Q1: what is the requiremen that would have resulted in the downgrade? Q2: We want to return to at least 125amp. SDGE suggested 2 options that don’t require replacing (ie trenching) the service wiring. Install a Remote Metering Device in existing panel or install a new 125 amp panel with 225amp busing. What are the advantages of one over the other?

 

[wwhitney]

The make and model of the inverter(s) and PV panels (and count), and of the service equipment, would be helpful in advising you.

1) The typical reason to do that is the "120%" rule which is one of the options for interconnecting the PV inverter output on the load side of the service disconnect. It says if you put the interconnection breaker at the opposite end of a panel bus as the utility breaker, then the sum of the breakers (or rather, 125% of the inverter output current) can be up to 120% of the bus rating.

So with a 125A bus and 125A main, the inverter breaker could be at most 25A (or rather, the inverter could be at most 20A or 4.8 kW). Downsizing the main breaker to 100A allows a 50A inverter breaker (or rather, inverter current of at most 40A, or 9.6 kW).

2) Not familiar with Remote Metering Device or how it would help. Upgrading the panel bus rating would allow putting back a 125A main breaker (assuming the inverter output current is between 20A and 40A, so that the downsize was originally necessary). You could possibly switch to a line side connection of the PV (between the meter and the main breaker), but the feasibility of that depends on the specific service equipment. If that would require replacing the service panel, then you might as well put in a larger panel and perhaps stick with your load side connection. Lastly, depending on the system size and degradation of the PV array, there is a possibility that downsizing the PV inverter to be 20A would be feasible without reducing the energy production significantly.

Cheers, Wayne

 

[jaggedben]

You implied that the service is underground when you mentioned trenching. If that's the case then by far the cheapest option is to replace the service panel with one that has higher rated busing and a 125A main breaker. This is totally possible to do, you just usually have to buy a 200A panel and replace the main breaker with a separately purchased 125A breaker. You do not need a 225A busbar unless you want to pay $$$$ to upgrade the underground service wires beyond what they were originally. The latter you would only need to do if you decided you really needed more grid power to the house.

Another question to ask is: Is this a centerfed panel? i.e. is the main breaker in the middle of the bussing? If so, under older codes the AHJ may have required the downsize whereas current code would not. In that case you don't have to do anything else if you just want to upsize the main breaker back to 125A. In order for this to be true the PV inverter output would have to be 20A or less, meaning the solar inverter breaker would probably be 25A or less.

What SDG&E said about remote metering device doesn't sound like they knew what they were talking about. Your primary authority on this should be your local building department, not SDG&E.

 

[HabitatSteve]

Thanks. Have a call in to Poway inspection to see if the 200A panel with 125A breaker is acceptable. It appears that may be our best option.

 

[curt swartz]

Check to make sure they will allow the 225 amp panel with 125 amp breaker. In PG&E territory they would require the underground substructures to match the size of the panel where their conductors terminate not the main breaker.

 

[wwhitney]

When subject to that limitation, you could use a 125A service disconnect (no distribution bus/breakers), with a 125A feeder to a 225A MLO panel to the same effect, right? You'd have an extra box on the wall, but I believe that as far as interconnecting at a breaker in the panel (i.e. not at the 125A feeder itself), it would otherwise be equivalent to a 225A panel with a 125A main breaker. Unless there's a corner case of NEC 705 I'm overlooking.

Cheers, Wayne

 

[GoldDigger]

LADWP will not allow a 200A panel unless you pay for a 200A service.

Sent from my Pixel 4a using Tapatalk

 

[curt swartz]

When subject to that limitation, you could use a 125A service disconnect (no distribution bus/breakers), with a 125A feeder to a 225A MLO panel to the same effect, right? You'd have an extra box on the wall, but I believe that as far as interconnecting at a breaker in the panel (i.e. not at the 125A feeder itself), it would otherwise be equivalent to a 225A panel with a 125A main breaker. Unless there's a corner case of NEC 705 I'm overlooking.

Cheers, Wayne

Yes, we have done similar to that for customers. Did one not long ago that customer wanted to add PV but companies they called said panel needed to be replaced first which involved a very complicated/expensive underground installation. We were doing a kitchen remodel and installed a single 125 amp main breaker at the service and fed a 225amp main lug loadcenter next to it. All new loads and existing loads were put in new panel. Told customer to call PV people again. Not sure if they ever did.

We have also installed quite a few 200 amp meter mains feeding 400 amp panelboards to allow for larger PV systems.

 

[wwhitney]

We have also installed quite a few 200 amp meter mains feeding 400 amp panelboards to allow for larger PV systems.

Is that easier/cheaper than using (2) MB 200A panels (one for loads, one for generation) with a a couple 3 port Polaris-style connectors (either in one of the 200A panels, or in a separate enclosure)? That would take advantage of the feeder interconnection rules to allow up to 200A of (125%) inverters and 200A of load without any components rated above 200A.

Cheers, Wayne

 

[curt swartz]

Is that easier/cheaper than using (2) MB 200A panels (one for loads, one for generation) with a a couple 3 port Polaris-style connectors (either in one of the 200A panels, or in a separate enclosure)? That would take advantage of the feeder interconnection rules to allow up to 200A of (125%) inverters and 200A of load without any components rated above 200A.

Cheers, Wayne

Its definitely easier since you don't have to put stuff together. Material cost wise is probably not much different by the time you add the cost of 2 loadcenters and all the connecting pieces. 400 amp panelbords are not bad price wise as long as supplier does it as a power quote and not normal stock prices.

I used a 400 amp NQOB panelboard and (2) 42 circuit on my own house a couple years ago. When my supplier had it quoted from SquareD the QO loadcenters and breakers were less expensive than I normally get HOM stuff for and I get get good pricing on HOM.

We have used the 400 panelboards as one of the feeders from the typical Class 320 Combination Service Entrance Devices that has (2) 200 amp service disconnects. Put the larger loads such as pool, electric dryer, stream shower, etc on one 200 amp breaker. Second breaker goes to the 400 amp panelboard. If Tesla Gateway or = is being installed it gets connected before panelboard.

 

[HabitatSteve]

Thanks for more suggestions. SDG&E initially suggested the 125A panel with 225A bus to avoid upgrading the service. Still waiting for answers from them about what they meant and allow. Although the current building permit was issued before 2020 code, the separate disconnect sounds like it would cover the new 2020 disconnect requirement. Does California require that disconnect. I’m in Minnesota but my 2nd residence (with daughter’s family) is in SD. I’m also waiting for Poway AHJ to respond so I can clear up some of what they will allow. Speed of response doesn’t seem to be on anyone’s agenda.

 

[jaggedben]

California will not be on the 2020 code until 2023.