Question on grounding rod for solar PV over two structures on the same property

[jaggedben]

My takeaway from the above is not seeing a compelling electrical safety reason to get involved questioning using building #2 as a passive mounting rack for the solar. Here I have the choice of saying nothing....
I'd feel better if building #2 had a lighting focused ground rod.

I'm assuming you mean lightNing when you say lighting. You mean an auxiliary ground rod for the solar array on building #2? I think that is a bad idea that misunderstands how lightning works. I'm no lightning protection expert, but I largely formed my opinion on this from this Mike Holt video from a few years back. Understand that just adding ground rods if you don't know what you're doing does not necessarily help avoid lightning damage and may make it worse. This has been put in and taken out of the code which explains how 690.47 evolved as it did.

 

[ggunn]

No, they are most certainly not. A service is a single circuit connection to a utility. That connection may be branched to multiple service disconnects that each have a meter.
See for example: https://www.gordonelectricsupply.co...er-Mp-Device-Ringless-125A-6-Position/5711484

Additionally, the NEC has a definition of a service and the NEC doesn't give a f--- if it's metered or not. The NEC prohibits multiple services to a building in most cases, without regard to how many occupancies one might wish to be separately metered. Every building with multiple meters that I've looked at closely had one service.

Maybe we are not talking about the same thing. Years ago I had to design a PV system for a condominium building with ~100 units. Each unit had its own meter and disconnect, and the POCO considered them to be separate services; we connected PV (microinverters) individually to each service. Yes, it was a pain.

 

[jaggedben]

Maybe we are not talking about the same thing. Years ago I had to design a PV system for a condominium building with ~100 units. Each unit had its own meter and disconnect, and the POCO considered them to be separate services; we connected PV (microinverters) individually to each service. Yes, it was a pain.

Perhaps that POCO uses the term 'service' in a way that doesn't match the NEC usage. (FWIW that's not my experience with the POCO around here.) Configuration of systems to qualify for net-metering or any other kind of interconnected metering is outside the scope of the NEC. The program our OP is using (Virtual Net Metering, VNEM) is designed precisely for the purpose of avoiding having to install 100 separate systems like you did. It is particular to California although other states might have similar programs.

 

[ggunn]

Perhaps that POCO uses the term 'service' in a way that doesn't match the NEC usage. (FWIW that's not my experience with the POCO around here.) Configuration of systems to qualify for net-metering or any other kind of interconnected metering is outside the scope of the NEC. The program our OP is using (Virtual Net Metering, VNEM) is designed precisely for the purpose of avoiding having to install 100 separate systems like you did. It is particular to California although other states might have similar programs.

What is the difference? With these 100 units, as I remember each had a disconnect connected directly (in a bus duct with no OCPD ahead of it) to conductors from the transformer servicing the building and a meter on the load side of the disco. The only thing different from a single family home service is that they were all on the same building. Does that make a difference? If there were a disco ahead of the bus duct would that have made a difference?

The POCO in question is or was working on a couple of pilot programs of the type you are referencing for virtual PV system metering for multifamily buildings, but at the time we built that PV system it was not yet in place. I don't know the results of the pilot programs.

 

[jaggedben]

What is the difference? ...

The difference is whether all the meters are paralleled to a single connection to the utility or not.

It is not uncommon to have 2-6 meters in a small apartment building connected to a service with lower ampacity than the sum of the meter disconnects. Say, 3 100A breakers after the meters connected to a 200A service, with a service mast under the scope of the NEC. So the total PV you could backfeed on that service would be 2/3rds of what it would be on 3 single family homes with 100A services. (Not that you would likely push that limit, but that's the difference. )

 

[ggunn]

The difference is whether all the meters are paralleled to a single connection to the utility or not.

It is not uncommon to have 2-6 meters in a small apartment building connected to a service with lower ampacity than the sum of the meter disconnects. Say, 3 100A breakers after the meters connected to a 200A service, with a service mast under the scope of the NEC. So the total PV you could backfeed on that service would be 2/3rds of what it would be on 3 single family homes with 100A services. (Not that you would likely push that limit, but that's the difference. )

It is still a bit murky to me. In a neighborhood of SFHs several homes will be connected in parallel to the same transformer, just as are the revenue meters on this condominium building. Why would it make a difference that the branch point is at the transformer rather than in a bus duct on the building? The POCO in this case did not see the connections as different.

 

[jaggedben]

It is still a bit murky to me. In a neighborhood of SFHs several homes will be connected in parallel to the same transformer, just as are the revenue meters on this condominium building. Why would it make a difference that the branch point is at the transformer rather than in a bus duct on the building? The POCO in this case did not see the connections as different.

To the case in point, if the Virtual Net Metering program regulations are written to only allow a PV system to offset billing for a group of meters connected to the same service - NEC definition - then the single family homes cannot sign up for the program. An apartment building with one service can.

The NEC cares if the bus duct belongs to the building owner and not the utility.

 

[ggunn]

To the case in point, if the Virtual Net Metering program regulations are written to only allow a PV system to offset billing for a group of meters connected to the same service - NEC definition - then the single family homes cannot sign up for the program. An apartment building with one service can.

The NEC cares if the bus duct belongs to the building owner and not the utility.

Can you point me to the NEC article that spells this out?

 

[jaggedben]

Can you point me to the NEC article that spells this out?

Article 100.
See particularly 'Service Point'.