Backfeeding via multiple subpanels

Kg808

Member
Hey everyone. I am bidding on a solar project and have a situation I haven't ran across before.

Pretty simple scenario: 18 KW system. 400 Amp main panel.

Option A: Ground mount all of the panels and just back feed straight to the main. Problem is there is limited 'unshaded' ground space available.

So my Option B: There are 3 dwellings on the same property all fed from the same meter/main (400A). Is there any reason I cannot install a roof mounted system w/ inverter on each dwelling?

Dwelling A: 100/100A end-fed sub panel - proposed 20A backfeed
Dwelling B: 100/100A End-fed Sub panel - proposed 20A backfeed
Dwelling C: 200/200A End-fed sub panel - Proposed 40A backfeed.

Total backfeed: 80A. which is totally doable for the 120% rule on the 400A main.

I have tied my backfeed OCPD into many sub panels before. But never ran into this situation to use multiple roof spaces and sub panels to backfeed one main/meter. Again just to be clear this is one meter feeding the entire property. Not an aggregated situation. And if it matters, I am in PG&E territory.

I'm hoping someone has ran into this before. I can't find anything that disallows this.


Thanks for your help and the free education.
 

ggunn

PE (Electrical), NABCEP certified
Hey everyone. I am bidding on a solar project and have a situation I haven't ran across before.

Pretty simple scenario: 18 KW system. 400 Amp main panel.

Option A: Ground mount all of the panels and just back feed straight to the main. Problem is there is limited 'unshaded' ground space available.

So my Option B: There are 3 dwellings on the same property all fed from the same meter/main (400A). Is there any reason I cannot install a roof mounted system w/ inverter on each dwelling?

Dwelling A: 100/100A end-fed sub panel - proposed 20A backfeed
Dwelling B: 100/100A End-fed Sub panel - proposed 20A backfeed
Dwelling C: 200/200A End-fed sub panel - Proposed 40A backfeed.

Total backfeed: 80A. which is totally doable for the 120% rule on the 400A main.

I have tied my backfeed OCPD into many sub panels before. But never ran into this situation to use multiple roof spaces and sub panels to backfeed one main/meter. Again just to be clear this is one meter feeding the entire property. Not an aggregated situation. And if it matters, I am in PG&E territory.

I'm hoping someone has ran into this before. I can't find anything that disallows this.


Thanks for your help and the free education.
You should probably check with the AHJ to see if they allow multiple PV interconnection points on the same service.
 

PVfarmer

Senior Member
Option A: Ground mount all of the panels and just back feed straight to the main.

use multiple roof spaces and sub panels to backfeed one main/meter. Again just to be clear this is one meter feeding the entire property. Not an aggregated situation.

I'm hoping someone has ran into this before. I can't find anything that disallows this.
.
Well, there is a PV disco involved with Option A, and it should be 10 feet from the meter, I beleive.

There also has to be something between the 3 main breakers of your PV subpanels and the meter.

So I say you'd need either 3 discos at the meter main, or perhaps an MLO panel for 3 breakers for the 3 structures, also at the meter main.

You can't put 3 separate PV discos on 3 separate structures with a meter main elsewhere, that's my opinion.
 

ggunn

PE (Electrical), NABCEP certified
You can't put 3 separate PV discos on 3 separate structures with a meter main elsewhere, that's my opinion.
It's not a code issue, it's a matter of what the AHJ wants, and different AHJ's want different things. I advise going to the AHJ and asking them.
 

jaggedben

Senior Member
@Kg808
I would submit plans to the AHJ and see what they say. Most likely in California it won't be an issue with them.

The most serious problem I think you are likely to run into is PG&E disconnect requirements. They are usually waived when the service is rated under 320A, but you've got a 400A service which may or may not be rated 320A in their eyes. (A lot of '400A' service equipment is really 320A continuous.) If you want to split up the system you need to make sure you are satisfying all their disconnect and signage requirements.


Well, there is a PV disco involved with Option A, and it should be 10 feet from the meter, I beleive.
You don't really know that.

You can't put 3 separate PV discos on 3 separate structures with a meter main elsewhere, that's my opinion.
Sure you can. I can't recall doing it with three structures, but I've done it with two, more than once.
 

Carultch

Senior Member
It's not a code issue, it's a matter of what the AHJ wants, and different AHJ's want different things. I advise going to the AHJ and asking them.
Could the AHJ disallow such a system, even if no part of the solution is against any NEC rule?

I can understand this being not allowed by the utility, but I thought the AHJ's enforcement is limited to what is written in the NEC and local/state codes.
 

ggunn

PE (Electrical), NABCEP certified
Could the AHJ disallow such a system, even if no part of the solution is against any NEC rule?

I can understand this being not allowed by the utility, but I thought the AHJ's enforcement is limited to what is written in the NEC and local/state codes.
The NEC does not carry the force of law; it is up to AHJ's to adopt it and they may amend it as they see fit.
 

BillK-AZ

Senior Member
Also a question of utility policy.

Several years ago while bidding on a Federal campus project I asked Arizona Public Service about this and their policy then was that they did not have a problem as long as there were six or fewer disconnect switches/production kWh meters and that all parts were accessible to their crews per the normal requirements.

SRP allowed two disconnect switches/production kWh meters on a residence with 400A service, backfeeding two 200A panels each with a 40A CB. The SES in this case had two 200A pull-out fuses and no provision for a third.
 

Kg808

Member
Thanks for the help and all the replies. But I agree I see no NEC issue with this installation. I'll ask my pge rep and plan check dept as well.

Ill post what what I find out for future reference.
 

PVfarmer

Senior Member
But never ran into this situation to use multiple roof spaces and sub panels to backfeed one main/meter.
It's probably new to your building inspector too, that's why I'd have solid reasons as to the "why+how" you feel you are allowed to do it.
I can't help you with those.

It's not a code issue, it's a matter of what the AHJ wants, and different AHJ's want different things. I advise going to the AHJ and asking them.
Actually, it's a matter of PG&E owning the meter.
I say their jurisdiction ends at the meter main load side breaker terminals.

There are some AHJs that people are aware of, but they don’t really consider them as AHJs:
Utility companies such as electrical, gas, telephone, and cable.
Zoning departments.
Elevator inspectors.
For the organizations, agencies, or departments listed above, each may have their own piece of a
project for which they regulate or control; their “jurisdiction.” And, within that jurisdiction they have the
“authority” to enforce compliance. For some AHJs, such as building departments, failure to comply with
their requirements could result in no certificate of occupancy, or possibly fines.

For others, noncompliance could result in termination of services (i.e. utility companies), no coverage under an insurance policy, or possible legal action.

But how do you know who all the AHJs are on a project? The answer: experience. There’s no single
source to go to that lists every conceivable AHJ applicable to a particular project type and location. A
good way to find out who the AHJs are on a project is to ask: ask the city or county, ask members on the
design team (including consultants), ask the owner (this may not be their first project in this location), and
ask colleagues who’ve worked on similar projects in the same area. I’m sure there are other sources of
information. In either case, eventually (maybe even a couple of years after project completion) you’ll
probably know who all the AHJs are on the project, as they’ll make their presence known if something
isn’t in compliance, or if the project didn’t go through their agency for review.
http://www.gridalternatives.org/sites/default/files/Linked documents/The Code Corner No. 9 - Authorities Having Jurisdiction.pdf


@Kg808
I would submit plans to the AHJ and see what they say.
The most serious problem I think you are likely to run into is PG&E disconnect requirements.

You don't really know that.

Sure you can. I can't recall doing it with three structures, but I've done it with two, more than once.
I'd find out exactly what PG&E wants done with the meter they own, *then* submit plans to the inspector.
That way they'll pass?

PG&E goes by the NE*S*C, they don't just make stuff up.
If you did it with 2 structures, maybe tell the OP how so he has some solid info to work with?
Again, arguing with me, as much as you seem to enjoy it, is kinda pointless.

Is there a 400A breaker with 3 sets of load side terminals?

The NEC does not carry the force of law; it is up to AHJ's to adopt it and they may amend it as they see fit.
PG&E owning the meter carries the force of law!
Also:
In summary, while the local AHJ has a lot of authority, in the end they can be overridden by OSHA inspectors and OSHA regulations. This is important to keep in mind, especially in cases where NEC special permission or waivers have been granted by the local AHJ.
http://www.ecmweb.com/nec/who-s-got-power

Also a question of utility policy.
Exactly. I can't see how a building inspector could say "no, you can't use a meter main approved by the POCO as it is rated to be used".

I see no NEC issue with this installation. I'll ask my pge rep and plan check dept as well.
I may be wrong/didn't look hard enough, but I don't see any 400A breakers with 3 load side terminals.
 

jaggedben

Senior Member
(Sigh)

It has essentially nothing to with PG&E owning the meter, and certainly nothing to do with the NESC. The disco requirements come from PG&E's PUC-approved interconnection agreement for a generating site. Otherwise it would be entirely up to the AHJ.

But yes, clarify the PG&E requirements before getting the permit, if you can.
 

PVfarmer

Senior Member
It has essentially nothing to with PG&E owning the meter, and certainly nothing to do with the NESC. The disco requirements come from PG&E's PUC-approved interconnection agreement for a generating site. Otherwise it would be entirely up to the AHJ.

But yes, clarify the PG&E requirements before getting the permit, if you can.
Doesn't the utility req. for a PV disco adjacent to the meter come from the NESC?

The utility wants to be able to disconnect the PV system from the meter, when there is a main breaker with the meter, sure the PV is technically "off" when you close the main, but there are still potentially live wires coming from the PV into the cabinet. Hence the common sense of having a switch or 3 adjacent to the meter main so the utility worker *knows* the PV is not connected.

If there is/are no PV disco adjacent to the meter main, you have a load side connection with breakers elsewhere.
 

ggunn

PE (Electrical), NABCEP certified
Actually, it's a matter of PG&E owning the meter.
I say their jurisdiction ends at the meter main load side breaker terminals.
The utility absolutely has a say in what you can connect to their system and what you can't if it is capable of backfeeding the grid. I deal with this stuff all day, every day.
 

PVfarmer

Senior Member
It's not a code issue, it's a matter of what the AHJ wants, and different AHJ's want different things.

The utility absolutely has a say in what you can connect to their system and what you can't if it is capable of backfeeding the grid.

I deal with this stuff all day, every day.
I find these two statements totally contradictory.
The OP's building inspector isn't going to explain what PG&E *requires*.

And no utility makes up special requirements, they have greenbooks.
Here is PG&E's, the reason why you can't do what the OP is proposing may be in here.
https://www.pge.com/en_US/business/services/building-and-renovation/overview/greenbook-manual-online/greenbook-manual-online.page

But I still think it's as simple as: there are no 400A breakers rated for 3 sets of conductors.

Have you seen a 400A breaker with that capability in your everyday dealings?
 

jaggedben

Senior Member
Doesn't the utility req. for a PV disco adjacent to the meter come from the NESC?
I don't think so, but instead of speculating about where PG&E's requirements come from, why not get them straight from the horses mouth. I regret not posting that link earlier.

The utility wants to be able to disconnect the PV system from the meter, [/QUOTE]

What I think they care about is disconnecting the PV system from their grid in the unusual case where a backfeed causes problems. They care less whether the PV system stays connected to the load side of the meter. A smart meter with a shutoff capability is one way they can meet their needs without requiring a discreet disconnect. But those don't come rated more than 320A. (I believe that's 320A continuous, so a 400A rated panel may still qualify, but I could be wrong and that's where the actual text of the panel label or a letter from a manufacturer will determine the outcome.)
 

jaggedben

Senior Member
But I still think it's as simple as: there are no 400A breakers rated for 3 sets of conductors.

Have you seen a 400A breaker with that capability in your everyday dealings?
KG808/OP-
There may be some relevant info here, the first two links should be pdfs from Eaton.
https://www.google.com/search?q=application+tap+rules+molded+eaton
Not relevant or helpful to the OP. 400A main could be feeding a panelboard which feeds all three subpanels, or any of several other arrangements. There's no reason to believe the OP has a problem with the equipment on site, that would be a whole other thread. Keep it on topic.
 

PVfarmer

Senior Member
400A main could be feeding a panelboard which feeds all three subpanels, or any of several other arrangements.
You'd rather argue with me than read- why?
Not reading their comments is...
"Not relevant or helpful to the OP."

I already suggestested the italicized back in comment #3. The OP did not say "oh we already have that", so...where'd you get it from?

Option A: Ground mount all of the panels and just back feed straight to the main.

I have tied my backfeed OCPD into many sub panels before. But never ran into this situation to use multiple roof spaces and sub panels to backfeed one main/meter.
 

jaggedben

Senior Member
Not reading their comments is...
"Not relevant or helpful to the OP."
Being an inexperienced person who doesn't know how to read their vocabulary is what's not helpful. "just back feed straight to the main" has meant the main panel, most of the hundreds of times people have said to me in the course of my work. It does not imply a supply side connection. But even if I'm making a wrong assumption there, it's off topic. The OP just asked if an AHJ will allow multiple PV sources to be connected at various locations. Line or load side at the main makes no difference to the answer to his question.
 

Kg808

Member
Ok... let's all play nice huh? you guys are going back and forth on semantics here. I understand I could've been a little more clear with my wording on my OP.

Pv farmer: I understand why you're concerned about 3 load side terminals on a main breaker. It's a 400a panel with a 200A split. 200A main feeding straight to the main house sub panel and a 200A main with attached 12/24 space distribution at the main panel. With 2 100 A breakers feeding sub panels at the other 2 structures.

and yes the main concern I had was wether or not I could mount on 3 separate buildings for the same pv system. Sorry if I over complicated it. The ampacities of the panels and breakers were just for a better picture of the system as a whole.

All these replies have been great help though. PGE has responded and said they have no problem with it as long as the signage is clear. Waiting on response from the AHJ.

Thanks again for the help.
 
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