Line-side-bus-tapped new main service off existing switchgear? (California)

[energywork]

Hi yall, I'm working on dev-phase design for a new (400a, 208/120v 3p) electrical service in an existing multifamily building in CA (San Diego City ahj, SDGE poco). Super space-limited, electrical room is pretty full, and there are no free meter hubs, or any place to install one in existing gear/meter bank (AFAIK), so i'm wondering if it would be allowable to:

Tap the utility line-side bussing in the gear (downstream from shared disconnect, upstream from existing tenant meter bank) and run conductors to a new meter/disconnect on the adjacent wall.

Specs are: service entrance fed from UG vault transformer adjacent to electrical room; 3000A Eaton/CutlerHammer switchgear/service entrance, bussing Ys, on the left is 1000a house service switchgear section; on the right is a 2000a shared disconnect and tenant meter bank. Looks like there's more space/access on the right side of the gear, so would expect to tap on that side (probably downstream of 2000a disco/upstream of meter bank), and run conductors in rigid conduit to the adjacent wall (~10-20' horizontal, ~20-30' conductor length with ups and downs, following NEC tap rules) where we could set a new 400a meter hub/disconnect.

(looking for whether this concept is allowable in general - from an NEC and utility electric service standards POV, could this kind of configuration even get approved? if yes, i'll worry about nuts-and-bolts of bussing config and exactly where/how to tap the Eaton gear as a secondary step. any specific codes or standards you could point me to that cover this would help)

An EE already took a look at the calcs and said there was plenty of amperage capacity, and thought it would be OK per NEC, but hadn't seen this done before and didn't know if SDGE would OK it; electrical subs we've talked to have been nervous about poco approval (idk about other states, but CA utilities can be challenging to work with for anything remotely nonstandard). Closest thing I've seen are line-side-tapped output-only meters for PV systems, which in physical/electrical config are pretty similar, but here we want to install a new bidirectional meter service (to land new heat pump electric water heater and new PV+ESS; with electric rate tarriff and pv value reasons to want to do this on a new separate meter). Nobody I've spoken with has been able to confidently say that it's allowed, but nobody has been able to point me to any written rule that would disallow it either, so I'm here.

Frequent lurker and first-time poster here, so hi! and thanks in advance!

 

[energywork]

cross-posted on reddit with photos and SLD here:

https://www.reddit.com/r/MEPEnginee...esidebustapped_new_main_service_off_existing/

 

[jaggedben]

Sounds like you want to do a 240.21(B) tap. I don't know why SDG&E should care as long as your meter location is acceptable to them. It sounds like you want to tap the switchgear manufacturers busbar, which usually requires either marked or documented tap points or field listing by UL, which is expensive. Building department probably matters a lot more than the utility here, you are not changing anything on the line side of the service disconnect.

 

[energywork]

Sounds like you want to do a 240.21(B) tap. I don't know why SDG&E should care as long as your meter location is acceptable to them. It sounds like you want to tap the switchgear manufacturers busbar, which usually requires either marked or documented tap points or field listing by UL, which is expensive. Building department probably matters a lot more than the utility here, you are not changing anything on the line side of the service disconnect.

That was my understanding also, but like i said i haven't been in this situation before personally. Outside of electrical service standards, any clue if a utility might have an issue with a second house meter (on a different rate schedule) from an accounts standpoint? (ask SDGE, i know, but they haven't been exactly helpful with information, so i'm just hoping to get a sense before investing in a meter spot)

 

[Joe.B]

I don't know about POCO, but the AHJ will probably have issue with a second meter in residential settings. They used to give 'em out like candy, but it makes it a lot easier to get an un-permitted second unit.

"POCO, I just need a separate meter for my shop. Hey Post Office, I just need a second mailbox so my moms junk mail doesn't get mixed with mine. Thanks y'all!"

Five years later, "What do you mean 'unpermitted', obviously it was approved. Duh."

 

[jaggedben]

That was my understanding also, but like i said i haven't been in this situation before personally. Outside of electrical service standards, any clue if a utility might have an issue with a second house meter (on a different rate schedule) from an accounts standpoint? (ask SDGE, i know, but they haven't been exactly helpful with information, so i'm just hoping to get a sense before investing in a meter spot)

My guess is that the utility will have no problem in principle giving you a extra meter on any rate schedule appropriate for the load on that meter. That is what they exist for. FWIW myself I have more often seen a utility insist on additional meters than refuse to provide them.

That said, I see you have a PV and ESS system on this tap. If you want to backfeed any PV to the grid, I hope you're not expecting it to meaningfully credit any other meters.
If you haven't already sorted out these questions, you're putting the cart before the horse in drawing up an SLD.

 

[energywork]

Thanks for weighing in guys. I don't think unpermitted adu will be a big AHJ concern here (this is ~75 unit affordable housing apartment site, highly managed/regulated, so basically 0 realistic risk of that, but i should check written rules about that). And no, no credit to other meters, PV/ESS would be solely for offsetting the new electric water heating load shown on this meter (which without additional PV will be quite pricey to operate, and we don't have enough room on site for addtl PV beyond that). New water heater has already been permitted on existing meter, but we could see better utility cost value by separating it.