7.6 Kw Inverter with 100-amp Service

[foo1bar]

Thank you for all the suggestions. In summary my main doubt is this: Do I satisfy the 120% rule if I'm using a 200-amp panel with a 7.6 KW inverter even thought the feeder cable and the service cable is rated for 100-amp? Is using a 200-amp panel with a 100-amp feeder cable in compliance with NEC?

You can always have a conductor (bus or wire) that is capable of carrying more amperage than the breaker/fuse protecting it.
And I think most panels you can replace the main breaker for it (ex. 200A) with a smaller one (ex. 100A)

The situation is that for residential accounts only one meter is allowed. So, I can't do a supply side tap. The integrated 100-amp combo meter/panel is old and I have not found an UL approved bus tap (the connection from the meter to the breaker is a bus, not a cable). The problem is that the combo meter/panel is in a concrete wall. And replacing it and/or making a tap (before or after the breaker) will be expensive.

Embedded in the concrete wall?
Not just inside a stucco wall or surface mount?
The builder must have really hated people.

The cheaper solution, in this case, would be to put a small 200-amp panel between the 100-amp combo meter/panel and the 100-amp distribution panel. Put a 100-amp input breaker and one 100-amp breaker to feed the distribution panel and one 40-amp breaker for the inverter. The only problem I have is that I'm not sure if this is acceptable under NEC. Does the 120% rule apply only to the panel where the inverter is connected, or do I need to replace the service and feeder cable with 200-amp cable?

So I think what you're saying that you currently have a combination meter-panel with a 100A breaker. And that feeds a 100A subpanel.
So you currently have

<meter>===<100A_breaker>==<2AWG_wire>== <100A_rated_subpanel_with_household_loads>

And you're planning to change that to be:

<meter>===<100A_breaker>==<2AWG_wire>==<200A_rat ed _subpanel>==<100A_breaker>==<2AWG_wire>== <exist_100A_subp>
.................................................. .........\\==<40A_breaker>==<inverter>

(ignore the periods, they're there to ensure spacing is good)

I do not know if you would have to have a 100A breaker at the top of that subpanel, or not.

I think you could do a 100A breaker at the top of the subpanel (fed from the meter panel), a 100A output breaker, a 40A backfeed breaker, and use a panel with a 125A rated bus and be compliant to the 120% rule. (125A * 1.2 = 150A)
I'm not a licensed electrician, but I think that'd meet the requirements for protecting the conductors. And probably be cheaper/more readily available than a 200A subpanel.

(and you should probably check the 2AWG for 100A - I didn't look that up, but since that's what you currently have for 100A from the main to the subpanel...)

[Markyrocks69]

The solution would be to replace the subpanel with a 200-amp sub panel. Use a 100-amp 2 pole breaker to backfeed (with hold down screw). And use a 40-amp breaker for the Inverter. The thing that make me doubt about this solution is that the 200-amp subpanel will still be feed by 100-amp cable (#2 AWG). Is this solution NEC compliant? Thank you very much.

Look man here's the simplest solution I can think of. Buy a cheap 100 amp subpanel. Open up your current distribution panel. Do a line tap before the 100amp breaker feeding that panel. Run the wires from the tap to the new sub. Slap a sticker on the new sub that says something to the effect of combined ampacity of breakers cant exceed ampacity rating of the busbar. Put the inverter breaker in the new subpanel.

Easy line tap

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F231380374626

[foo1bar]

Look man here's the simplest solution I can think of. Buy a cheap 100 amp subpanel. Open up your current distribution panel. Do a line tap before the 100amp breaker feeding that panel. Run the wires from the tap to the new sub. Slap a sticker on the new sub that says something to the effect of combined ampacity of breakers cant exceed ampacity rating of the busbar. Put the inverter breaker in the new subpanel.

Are you assuming there's a 100A breaker already in the current distribution panel? (ie. that there's a 100A breaker at each end of the wires between the main panel and the distribution panel.)?

If it is instead a main-lug panel, there could be 100A coming from the main breaker in the combo meter panel, and 40A coming from the solar through the tap. That would be 140A on the 100A distribution panel bus bars (not allowed). And also 140A on the wire between the lugs and the tap (also not OK).
If it is a distribution panel that has a 100A main breaker, then that possible (although admittedly unlikely) situation goes away.

[Markyrocks69]

Are you assuming there's a 100A breaker already in the current distribution panel? (ie. that there's a 100A breaker at each end of the wires between the main panel and the distribution panel.)?

If it is instead a main-lug panel, there could be 100A coming from the main breaker in the combo meter panel, and 40A coming from the solar through the tap. That would be 140A on the 100A distribution panel bus bars (not allowed). And also 140A on the wire between the lugs and the tap (also not OK).
If it is a distribution panel that has a 100A main breaker, then that possible (although admittedly unlikely) situation goes away.

I'm assuming that there is a 100 amp main breaker in his distribution panel. There would have to be unless its within 5ft of the meter/main disconnect. I'm thinking about this and yes you are correct. If there isn't a 100 amp breaker in the panel then my solution wouldn't work.

there is always the the possibility if there isn't a main breaker in the current distribution panel of just removing the wires from the busbar and installing a 100amp breaker on the bus and connecting the power cables to the breaker so then that panel bus would be protected from the tap. Then there shouldn't be a problem doing a tap b4 that new breaker AS LONG AS the meter/main disconnect doesn't allow more breakers to be installed.



I want to revise my previous answer. The simplest solution is to remove existing power wires to the bus of the distribution panel, add the 100amp breaker, connect the power to the breaker (backfed), connect the inverter circuit directly to the main power wires inside of the panel via a tap. Obviously you need a disconnect in between.

[josepr]

Thank you very much for the suggestions. I think that the two solutions provided (200 or 125 amp subpanel or the tap with the back-feeding 100 amp breaker and 40 for the inverter) should work and be compliant with the NEC. If for some reason the electrician disagrees I think that I can downgrade the 100 amp breaker to 80 amp and do any of the two solutions provided. Again, thank you very much for your suggestions.

[Markyrocks69]

Thank you very much for the suggestions. I think that the two solutions provided (200 or 125 amp subpanel or the tap with the back-feeding 100 amp breaker and 40 for the inverter) should work and be compliant with the NEC. If for some reason the electrician disagrees I think that I can downgrade the 100 amp breaker to 80 amp and do any of the two solutions provided. Again, thank you very much for your suggestions.

For the record I believe you could put in a 200 amp subpanel and it would still be code compliant. Even if you bought a main panel with a bolt in 200amp breaker in it you probably could just leave it in there. The reasoning being the wires coming from the meter cabinet would always be protected by the 100amp main service disconnect.

The only other thing I can add is if you used the backfed breaker scenario with a tap. There is no need for a 40 amp breaker in the distribution panel. You could either use a molded case breaker or a fused disconnect. Youd have to find out what the local rules are.

This thread got me thinking about my pv system that I'm working on and I'm pretty sure I'm in violation. It's one of those things where I doubt mr magoo my electrical inspector would catch it but I'm thinking I have no choice but to do a load side tap. My situation is similar to yours bc my main disconnect is 100 ft away from my house. But I need 2x 40 amp breakers in my 200 amp "sub" panel. I had actually installed an additional 125 amp sub panel bc my main is pretty full. But revisiting this topic the power flow from my panels would still land on the busbars of my main distribution panel through the breaker that feeds my sub.... so I guess I'd need a 400amp busbar to be compliant or do a load side tap. Gawd I'm never going to finish this project.