back-fed breaker and generator interconnect

[RustyShackleford]

My jurisdiction allows line-side taps, as well as back-fed circuit breakers, for connecting a grid-tied solar inverter.

They also allow interlock kits (in the main load center) for generator inlets.

If using both a back-fed breaker for the PV inverter, AND an interlock kit for the generator inlet, it seems that a hazard exists. During generator usage, the interlock prevents both the main breaker and the breaker for the generator inlet from being turned on at the same time. However, it'd still be necessary to remember to turn off the back-fed PV breaker; otherwise the generator and the PV inverter could be connected to each other (via the load center busbars) with unexpected and probably bad results.

Is there any way for a back-fed PV inverter connection to co-exist with a generator inlet, other than using a critical-loads sub-panel for the generator ? There are no interlock kits I'm aware of that work with three breakers (the main breaker, the generator-inlet breaker, and the PV-inverter breaker).

 

[LarryFine]

Wouldn't the inverter function with the genny like it does the utility?

 

[wwhitney]

Wouldn't the inverter function with the genny like it does the utility?

Yes, which is the problem, as a grid can absorb power put out by the inverter, for the case that PV production exceeds local loads, but the generator can not.

Cheers, Wayne

 

[solarken]

I agree it is a problem to do a load side interconnection that is common with the generator. Easiest solution would be to tap the mains and do a supply side solar interconnection, that is islanded with the grid when the grid goes down, leaving the generator alone to power the loads in a grid outage. Or install a transfer switch or contactor between the back-fed breaker and the solar inverter with grid sensing that disconnects the inverter during a grid outage.

Supposedly, enphase can co-exist operationally with a generator while islanded, but I have not tested it. I believe their approach leverages the possibility that they can granularly control how many microinverters are producing based on the needs of the load.

 

[ggunn]

My jurisdiction allows line-side taps, as well as back-fed circuit breakers, for connecting a grid-tied solar inverter.

They also allow interlock kits (in the main load center) for generator inlets.

If using both a back-fed breaker for the PV inverter, AND an interlock kit for the generator inlet, it seems that a hazard exists. During generator usage, the interlock prevents both the main breaker and the breaker for the generator inlet from being turned on at the same time. However, it'd still be necessary to remember to turn off the back-fed PV breaker; otherwise the generator and the PV inverter could be connected to each other (via the load center busbars) with unexpected and probably bad results.

Is there any way for a back-fed PV inverter connection to co-exist with a generator inlet, other than using a critical-loads sub-panel for the generator ? There are no interlock kits I'm aware of that work with three breakers (the main breaker, the generator-inlet breaker, and the PV-inverter breaker).

A PV system needs to be connected on the line side of the generator connection whether the generator is connected through an ATS or a backfed breaker with an interlock kit. Otherwise the PV could backfeed the generator, which would be bad news for the generator.

 

[RustyShackleford]

A PV system needs to be connected on the line side of the generator connection whether the generator is connected through an ATS or a backfed breaker with an interlock kit. Otherwise the PV could backfeed the generator, which would be bad news for the generator.

Ok, what I thought, just wanted to make sure I wasn't missing anything.

Except, the ATS isolates the generator from the main panel, so if the back-fed PV breaker is in the main panel, that should be ok, right ?

 

[ggunn]

Ok, what I thought, just wanted to make sure I wasn't missing anything.

Except, the ATS isolates the generator from the main panel, so if the back-fed PV breaker is in the main panel, that should be ok, right ?

Not usually. Most of the time the ATS switches the feed to the panel from the grid to the generator, so if the PV connection is in the panel then it is connected to the generator when the ATS trips.

 

[Seven-Delta-FortyOne]

I don’t work with solar, so forgive me if I’m mistaken on this, but it sounds like if you have the backfed PV breaker in the main panel, the best option would be a load side ATS somewhere downstream of the main panel.

If I was doing a gen with solar, I believe that’s how I would do it. Since the feed from the panel to the ATS has both utility and solar, the ATS should shut off both, and the house would run on only gen power during an outage.

I’ve explored this with a few folks, and combining utility, generator, solar, and battery backup can get very complicated.

 

[ggunn]

I don’t work with solar, so forgive me if I’m mistaken on this, but it sounds like if you have the backfed PV breaker in the main panel, the best option would be a load side ATS somewhere downstream of the main panel.

If I was doing a gen with solar, I believe that’s how I would do it. Since the feed from the panel to the ATS has both utility and solar, the ATS should shut off both, and the house would run on only gen power during an outage.

I’ve explored this with a few folks, and combining utility, generator, solar, and battery backup can get very complicated.

True dat, but for a straight grid tied PV system (no batteries) and a generator, if you want the generator to back up everything in the main panel, you would install the ATS ahead of the panel and the PV tapped to the service conductors ahead of the ATS.

 

[LarryFine]

So, the panel is fed either from the utility and the PV system, or from just the genny.

 

[Seven-Delta-FortyOne]

True dat, but for a straight grid tied PV system (no batteries) and a generator, if you want the generator to back up everything in the main panel, you would install the ATS ahead of the panel and the PV tapped to the service conductors ahead of the ATS.

So 2 line side taps? PV first, then ATS?

Here, PG&E is cracking down on line side taps, so they are not an option here.

Talked with a PG&E rep this morning, and he said "we've basically pissed off every electrical contractor in the county at this point".

 

[RustyShackleford]

Here, PG&E is cracking down on line side taps, so they are not an option here.

Why they no like them ? Still gotta have an AC disconnect between taps and PV inverter.

Of course, it's a bit scary that there's no overcurrent protection anywhere between the taps and the transformer.

 

[Seven-Delta-FortyOne]

Don’t know. It’s mostly about “customer supplied equipment on OUR side”.

I suggested they bring their own taps. No go.

If I tap the conductors on the customer side before the MCB, they want an NRTL to sign off that I’ve ”modified the panel” and it’s OK. Or the inspector to write that he doesn’t require it. (He doesn’t).

But then there’s still the issue of the N-G bond, which there’s no good way to solve.

They’re on a runner right now…..

 

[jaggedben]

...

Supposedly, enphase can co-exist operationally with a generator while islanded, but I have not tested it. I believe their approach leverages the possibility that they can granularly control how many microinverters are producing based on the needs of the load.

This is supported through the Enphase System Controller which has relays for grid PV, battery and generator, and software to control when they are connected to each other.

 

[ggunn]

So 2 line side taps? PV first, then ATS?

Here, PG&E is cracking down on line side taps, so they are not an option here.

Talked with a PG&E rep this morning, and he said "we've basically pissed off every electrical contractor in the county at this point".

An ATS is not a tap; when the generator is connected to the main panel the grid is disconnected from the panel. The PV connection is a tap on the service conductors on the line side of the ATS and on the customer's side of the meter; when the grid goes down the ATS switches the feed to the panel from the grid to the generator, and the PV system shuts off.

If you bring batteries into the equation, everything changes.

 

[jaggedben]

FWIW there are many ways to skin this cat without any 'taps', formal or informal.
For example: main panel with PV -> Subpanel with interlock kit
Or: Main breaker -> Subpanel with PV -> ATS -> Backed up Panel
All depends on the details.

Don’t know. It’s mostly about “customer supplied equipment on OUR side”.

I suggested they bring their own taps. No go.

If I tap the conductors on the customer side before the MCB, they want an NRTL to sign off that I’ve ”modified the panel” and it’s OK. Or the inspector to write that he doesn’t require it. (He doesn’t).

But then there’s still the issue of the N-G bond, which there’s no good way to solve.

They’re on a runner right now…..

I don't exactly understand this. For a factory meter/main assembly they are quite right to expect that, IMO. Are people really trying to modify those? Are the AHJs allowing stuff in your area that most wouldn't? I have no love for PG&E but I can understand them pushing back if they are seeing a lot of hack installations. Then again, around here they mostly never even come out to look.

 

[Seven-Delta-FortyOne]

FWIW there are many ways to skin this cat without any 'taps', formal or informal.
For example: main panel with PV -> Subpanel with interlock kit
Or: Main breaker -> Subpanel with PV -> ATS -> Backed up Panel
All depends on the details.



I don't exactly understand this. For a factory meter/main assembly they are quite right to expect that, IMO. Are people really trying to modify those? Are the AHJs allowing stuff in your area that most wouldn't? I have no love for PG&E but I can understand them pushing back if they are seeing a lot of hack installations. Then again, around here they mostly never even come out to look.

I’m in your area. I’m in Humboldt.

Some of these panels have wire conductors from the meter to the MCB. It has been my opinion, and my inspectors agree, that I can move those conductors off the MCB in the panel, and re-route them to an ATS. It’s been discussed here a few times as well, and I understand that not everyone agrees with me.

If the panel is label “for service entrance only”, I could see that texhnically being a violation, as that main panel is now a sub panel. Except it still contains the meter.

I would say it’s a grey area at least.

 

[LarryFine]

If the panel is label “for service entrance only”, I could see that texhnically being a violation, as that main panel is now a sub panel. Except it still contains the meter.

What would be better is a way to intercept the current pathway after the main breaker, like removable links.

 

[Seven-Delta-FortyOne]

What would be better is a way to intercept the current pathway after the main breaker, like removable links.

Those are my favorite panels to work with. Either those or the Eaton panel that has a main/no distribution, and feed through lugs at the bottom.

It interesting that every single one of these set ups are after the main breaker, which makes an SE-Rated ATS unnecessary. And yet the manufacturers make them and sell them all over.

If you’re not doing a line side tap, you don’t need it.

 

[gene6]

Some of these panels have wire conductors from the meter to the MCB. It has been my opinion, and my inspectors agree, that I can move those conductors off the MCB in the panel, and re-route them to an ATS.

When you say wire conductors are you talking about a the factory installed conductors between the meter and the main in a panel that has the meter integrated into the panel AKA a 'trailer panel'? You removing the factory service conductors in a panel like this: ?