120 % NEC rule and Panel labels

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wwhitney said:
Does not apply as the top breaker (which I hadn't realized is only 100A) does not have a busbar.

So the OP could interconnect 100A (after 125%) of PV via that 100A feeder, as long as the panel supplied by the 100A feeder has a main breaker. E.g. bring the PV conductors into the top section and splice to the 100A feeder. The PV conductors would need to satisfy a tap rule.

Jaggedben's proposal is a cleaner but requires an extra panel.

Cheers, Wayne
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You are correct, I didn’t notice that this was Square D and that the meter conductors go straight into the breaker. Be careful though: same situation on a different manufacturer (like Siemens) actually has a little tiny bus and uses a normal stab main breaker. I’m not sure if the 120% rule truly would identify that as a bus or not since it’s dedicated to just that second disconnect. We use that second disconnect often with a dedicated AC recombiner panel, although Siemens now makes a 400a panel with a dedicated PV section separate from both 200a disconnects.

It would be simple to do a load side tap off of that 100a breaker as long as there’s an upstream main breaker sized to the feeders. A main breaker panel would work fine, unless a blade style fused disconnect (or even a safety switch to a main breaker) was required by the AHJ or utility.

Good discussion on how to overcome interconnection challenges.

The 200a solar ready Square D options now have a lug kit for their bus bars, haven’t had to use it yet — but pretty impressive.
 
BackCountry said:
Be careful though: same situation on a different manufacturer (like Siemens) actually has a little tiny bus and uses a normal stab main breaker. I’m not sure if the 120% rule truly would identify that as a bus or not since it’s dedicated to just that second disconnect.
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Good to know, but a bus with only one breaker on it would qualify under the "sum of all breakers" rule, so you wouldn't have to worry about the 120% rule.

Cheers, Wayne
 
As other have said, it looks like your best bet is to tap the 100A feeder conductors that land on the top service disconnect in the panel. It those feeder conductors don't have an OCPD on their load end, you will need to install that. If the conductors you use to make the interconnection are rated at 100A, I don't believe that is technically considered a tap, and so you wouldn't have to follow the tap rules. Just run the circuit into a 6-space 100A MLO load center and land your inverter circuits in there. Of course you will have to meet the Rapid shutdown rules and utility requirement, which may dictate additional disconnects.
 
BackCountry said:
Absolutely. This is a simple one.

And you’d probably be ok to use a “vampire” style inline taps on the feeders feeding each breaker from the meter section; however, that’s a listed assembly so it could get rejected.

Your best bet is to simply use the 120% rule with what you’ve already got, 120%x200a rating=240-100a existing breaker=140a net backfeed, so 80a or 15kw should be no problem.

Remember to apply early, 15kw should only be a problem if your service happens to be fed by a 10kva tx from the utility and you’re the solo customer.
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Buchanan makes a UL listed tap (BTap) that says “suitable for use on line side of the service equipment”. Just failed an inspection for using an ilsco and the Burndys aren’t suitable but UL listed. This has been an issue since the first of the year everywhere but this is the only device I found that is suitable for line side of service equipment. Buchanan BTap Cat # BTC4/0-10 is what I used and has a tap rating of up to 130 amps (which you’ll never get to off res solar), misinterpreted thinking it was the service amperage.
 
Eliminate unnecessary material costs altogether and install a new transfer switch alternative called the Solar Interlock Kit.
It allows for load side installation of the PV system as well as a secondary power option like a generator! This product installs in accordance with the 120% buss rule. Also certified for use with UL 67 panelboards and accepted by all AHJ's i am aware of!
 
Electricman7 said:
Eliminate unnecessary material costs altogether and install a new transfer switch alternative called the Solar Interlock Kit.
It allows for load side installation of the PV system as well as a secondary power option like a generator! This product installs in accordance with the 120% buss rule. Also certified for use with UL 67 panelboards and accepted by all AHJ's i am aware of!
Click to expand...
All the interlock kits I have seen, including what I see when I google "Solar Interlock Kit" are simply devices that prevent a main breaker and a backfed load breaker from a generator to be on at the same time. You should never connect a PV system to another backfed breaker in a panel with one of these devices installed; doing that would connect the PV system to the generator when the main breaker is off and the generator breaker is on.

Maybe what you are seeing is something else?
 
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