26kW residential system?

Any ideas on how to add, without a service upgrade, 20kW (two 10kW inverters) to an existing 6kW system on a residential property serviced with a main panel (200A), a sub panel (100A) and a sub sub panel?

The existing PV system (6kW) was installed with a 30A breaker located immediately adjacent to the center-fed 200A main breaker. It's been in place for 10 years.

The local utility (SDG&E), does not permit line-side taps, but does offer a Renewable Meter Adapter (RMA) which features a 60A breaker.

Options?

The owner of the property has already purchased all of the equipment (60 panels and 2 10kW inverters) and is now looking for a contractor for installation.
 
Any ideas on how to add, without a service upgrade, 20kW (two 10kW inverters) to an existing 6kW system on a residential property serviced with a main panel (200A), a sub panel (100A) and a sub sub panel?

The existing PV system (6kW) was installed with a 30A breaker located immediately adjacent to the center-fed 200A main breaker. It's been in place for 10 years.

The local utility (SDG&E), does not permit line-side taps, but does offer a Renewable Meter Adapter (RMA) which features a 60A breaker.

Options?

The owner of the property has already purchased all of the equipment (60 panels and 2 10kW inverters) and is now looking for a contractor for installation.
Is that normal to not allow a line side tap? I might try to figure out the reasoning behind that and clarify that's how it really is.
 
Is that normal to not allow a line side tap? I might try to figure out the reasoning behind that and clarify that's how it really is.
I wouldn't say it is normal, but I have heard of this silly requirement by some utilities. One option is to use 230.40 exception #2, which really is just what a supply side connection is anyway, and qualify the busbar on the panelboard serving the pv with the "sum of all over current devices" provision.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Is that normal to not allow a line side tap? I might try to figure out the reasoning behind that and clarify that's how it really is.
We deal with an AHJ that does not allow line side PV interconnections, as well as a couple who allow nothing but them. That's just one of the differences; we keep an evolving document on the different rules in different jurisdictions in Texas. It's up to five pages now, I believe.
 
Any ideas on how to add, without a service upgrade , 20kW (two 10kW inverters) to an existing 6kW system
One option is to use 230.40 exception #2 , which really is just what a supply side connection is anyway, and qualify the busbar on the panelboard serving the pv with the "sum of all over current devices" provision.
Just wanted to add a little more to this. Note you could do this without a service upgrade. 230.90(A) exception #3 allows the sum of the OCPD's service as the service disconnect to exceed the ampacity of the service conductors, so you could leave the meter and everything upstream as is. Tap the conductors on the load side of the meter into two sets, add a new panelboard to the new set and make a load side connection in it.
 

jaggedben

Senior Member
mcsolar

No, you can't do this without changing the service equipment. (You don't need to upgrade the service, just the service equipment.) Electrofelon has the right idea, just create a second service disconnect. Put in a meter socket, gutter, replace the existing with a 200A panel (not meter/main) and put in a separate 125bA for the solar.

I'm skeptical that SDG&E can really disallow supply side connections in general, but if you've got a meter/main combo it makes no difference. You have to replace that.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
I'm skeptical that SDG&E can really disallow supply side connections in general...
But an AHJ can, and they do. As we have discussed many times, an AHJ can amend the NEC in any way they see fit within their area of jurisdiction. They can add restrictions that aren't in the code and they can choose not to enforce some that are.

We operate throughout the state of Texas, and in doing so we have encountered two AHJs that completely prohibit line side connected PV as well as a couple that require all PV to be line side connected. One of them has added a restriction that virtually disallows any PV interconnection in a subpanel, even though the way it is (poorly) written into their Interconnection Guide belies a misunderstanding of basic electrical theory. We challenged it and lost the fight.

It would be great if all AHJ's looked at PV the same way, but that ain't gonna happen.
 

jaggedben

Senior Member
IOUs in California are not AHJs. And AHJs in California can't make their own rules without going through a specific process with the state. So we don't get as much variation out here on this stuff.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
IOUs in California are not AHJs. And AHJs in California can't make their own rules without going through a specific process with the state. So we don't get as much variation out here on this stuff.
Lucky you. :D
 

wwhitney

Senior Member
Location
Berkeley, CA
What am I missing--how is a second service disconnect that only serves PV any different from a line-side tap? Or is the idea to put a little load on the second service disconnect, too?

Another option is that if a 200A service disconnect can be added in front of the existing 200A main panel, then the 200A feeder from the new service disconnect to the main panel can be tapped per 705.12(D)(2)(1).

Cheers, Wayne
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
A
The owner of the property has already purchased all of the equipment (60 panels and 2 10kW inverters) and is now looking for a contractor for installation.
This is usually a mistake. A PV system should be completely designed, including the interconnection, before the first dime is plunked down, and whoever designed it should be on the hook if anything is amiss. This is especially true if the customer isn't an electrical contractor experienced in PV systems.

We are in the process now of trying to help two individuals who are in dire straits because they tried to go DIY and ended up with equipment that they cannot interconnect. Both are the victims of unscrupulous salespersons.
 
What am I missing--how is a second service disconnect that only serves PV any different from a line-side tap? Or is the idea to put a little load on the second service disconnect, too?
Sounds the same, only explained differently, but maybe that's the point? Just don't call it a line-side tap? I don't understand SDG&E's position - what about 705.12(A)? but their "NEM Team" netmetering@semprautilities.com wrote "We do not permit line-side taps on residential properties. Commercial customers can have line-side taps for Virtual Net Metering applications only."

Maybe, if they are willing, a meeting with the AHJ and a review of the situation and some of the options presented here is the best approach.

Sounds like there are a few options, thank you everyone for the help.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Sounds the same, only explained differently, but maybe that's the point? Just don't call it a line-side tap? I don't understand SDG&E's position - what about 705.12(A)? but their "NEM Team" netmetering@semprautilities.com wrote "We do not permit line-side taps on residential properties. Commercial customers can have line-side taps for Virtual Net Metering applications only."

Maybe, if they are willing, a meeting with the AHJ and a review of the situation and some of the options presented here is the best approach.

Sounds like there are a few options, thank you everyone for the help.
Good luck with that, but it looks like the AHJ is dead set against supply side PV interconnection. It happens; the AHJ isn't necessarily required to allow everything that the NEC allows. If the "NEM Team" is acting within the bounds of their authority you may have to do something else.

You could install a larger MDP with the presently sized OCPD to make room for the PV under the 120% rule.
 

jaggedben

Senior Member
Sounds the same, only explained differently, but maybe that's the point? Just don't call it a line-side tap? I don't understand SDG&E's position - what about 705.12(A)? but their "NEM Team" netmetering@semprautilities.com wrote "We do not permit line-side taps on residential properties. Commercial customers can have line-side taps for Virtual Net Metering applications only."

Maybe, if they are willing, a meeting with the AHJ and a review of the situation and some of the options presented here is the best approach.

Sounds like there are a few options, thank you everyone for the help.
I don't work with SDG&E but with PG&E I wouldn't have bothered asking them. They would like to know, but the only person whose sign-off I care about is the AHJ. For residential that is. I don't need PG&E to tell me the right way to do it because I know.

Again, if you can get the AHJ to agree to a compliant service configuration I would not accept that answer from the utility. (And for ggunn, the utility is not the AHJ here!) I certainly wouldn't just back down after one email that didn't cite a policy document. It may just be that meter main combos are so preponderant that they are in the habit of telling people it's not allowed because they don't see too many situations where it would work.
 

jaggedben

Senior Member
What am I missing--how is a second service disconnect that only serves PV any different from a line-side tap? Or is the idea to put a little load on the second service disconnect, too?

Another option is that if a 200A service disconnect can be added in front of the existing 200A main panel, then the 200A feeder from the new service disconnect to the main panel can be tapped per 705.12(D)(2)(1).

Cheers, Wayne
It's a code section that one cites as a way of pointing out that their purported prohibition is illegal. Get the actual AHJ to sign off on the service configuration and there's not much they can say.

As for the other option... might as well just replace the service equipment. Unless it turns out that the meter and panel are in separate enclosures, but the 'centerfed' remark suggests otherwise.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Again, if you can get the AHJ to agree to a compliant service configuration I would not accept that answer from the utility. (And for ggunn, the utility is not the AHJ here!...
Hence my disclaimer: If the "NEM Team" is acting within the bounds of their authority you may have to do something else, "if" being the operative. Here in Texas we sometimes have dueling AHJ's (cue the music from "Deliverance") where the utility and the city both have their rules, and we have to comply with both sets.
 
It's a code section that one cites as a way of pointing out that their purported prohibition is illegal. Get the actual AHJ to sign off on the service configuration and there's not much they can say.

As for the other option... might as well just replace the service equipment. Unless it turns out that the meter and panel are in separate enclosures, but the 'centerfed' remark suggests otherwise.
I thought about just getting the permit per code, but worry the utility would refuse to power down to allow the work to be performed, or that the utility and the AHJ are aligned and the AHJ has ultimate authority and they'll be the ones to enforce SDG&E's position.

Also thought about replacing the center-fed 200A panel with a 400A panel but had an electrician warn that the service itself (underground service coming in from the street) might only be 200A and so that it was a bad idea.
 
Also thought about replacing the center-fed 200A panel with a 400A panel but had an electrician warn that the service itself (underground service coming in from the street) might only be 200A and so that it was a bad idea.
There would be nothing wrong with that. You don't need to upgrade the service, you just need to upgrade the panelboard to meet the 120% rule. You could get say a 400 amp bus panel with a 200 amp main breaker. That would be factory order panelboard and probably bolt on breakers so it wouldn't be super cheap, but it would look nice.
 

jaggedben

Senior Member
You could also meet 705.12(D)(2)(3)(c) by using a 400A panel with a 200A breaker to a new sub for the loads and a 125A breaker to a sub for the three inverters. You can put in a 200A main breaker so as not to have to upgrade the service conductors. And that will get you around this stupid line side tap issue. But you still have to replace the service equipment.
 
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