Solar & Subpanel

BatikikikBatikikik Solar Expert Posts: 141 ✭✭✭✭✭
Hello guys ,

We have house with 600A main panelboard .
Thah house has 3 subpanels each one 200A .
We have 20kW solar photovoltaic system with 2 SB8000US .
Each Sb8000US require 40A breaker .
My question is can we connect those 2 inverter breakers to the subpanel (200A), or we have to connect to the main(600A) ????

Thank you

Comments

  • Solar GuppySolar Guppy Solar Expert Posts: 1,989 ✭✭✭
    Re: Solar & Subpanel

    What did your licensed electrical contractor document for the permit application?
  • solar_davesolar_dave Solar Expert Posts: 2,395 ✭✭✭✭
    Re: Solar & Subpanel

    in theory you could derate either one panel with 125amp main breaker or 2 panels with 175 amp main breakers. it is all dependent on what the local code enforcement will allow on your installers design.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Solar & Subpanel

    Couldn't he just install one 40A backfed breaker in each of two of the subpanels at the opposite ends of the busbars from the main breakers and stay within the 20% rule?
  • Solar GuppySolar Guppy Solar Expert Posts: 1,989 ✭✭✭
    Re: Solar & Subpanel

    "He", being a contractor, should not be guessing at this. There is zero need for us to explain the NEC rules, as a contractor for hire, "he" should be using a licensed master electrician and that electrician would be submitting all the require design paperwork to satisfy the local building department requirement.
  • BatikikikBatikikik Solar Expert Posts: 141 ✭✭✭✭✭
    Re: Solar & Subpanel

    Solar Guppy looks like your mama born you electrician a ???
    Why are you getting mad, thats why forum is to learn and change experience.
    If you dont want to do dont give advices but dont tell stupid things because everybody are learning here and nobody want to read your idiot ideas and nobady in the world knows 100%.And I am sure on electrical I can explain you a lot of things that you have no idea about that , so dont tell here that you are bigg boss and we does not know anything .

    - Guys my opinion is , I can connect 2 solar breakers each one 40A to one subpanel which has 100A main breaker and that will be fine because 80+100=180A

    If main is 200A . max you can connect is 40A.
    If main is 175A . max you can connect is 35A.

    If I am wrong tell me :)))))
  • JburgessJburgess Solar Expert Posts: 130 ✭✭✭
    Re: Solar & Subpanel
    Batikikik wrote: »
    - Guys my opinion is , I can connect 2 solar breakers each one 40A to one subpanel which has 100A main breaker and that will be fine because 80+100=180A

    If main is 200A . max you can connect is 40A.
    If main is 175A . max you can connect is 35A.

    If I am wrong tell me :)))))

    200 * 1.2 =240 amps max feed

    240 – 200 main = 40 amp max solar feed
    240 – 175 main = 65 amp max solar feed
    240 – 150 main = 90 amp max solar feed
  • jeffkrusejeffkruse Solar Expert Posts: 205 ✭✭✭
    Re: Solar & Subpanel
    Batikikik wrote: »
    Solar Guppy looks like your mama born you electrician a ???
    Why are you getting mad, thats why forum is to learn and change experience.
    If you dont want to do dont give advices but dont tell stupid things because everybody are learning here and nobody want to read your idiot ideas and nobady in the world knows 100%.And I am sure on electrical I can explain you a lot of things that you have no idea about that , so dont tell here that you are bigg boss and we does not know anything .

    - Guys my opinion is , I can connect 2 solar breakers each one 40A to one subpanel which has 100A main breaker and that will be fine because 80+100=180A

    If main is 200A . max you can connect is 40A.
    If main is 175A . max you can connect is 35A.

    If I am wrong tell me :)))))


    You are wrong and SG is correct. If you are an installer and getting paid for this you should be using a licenced electrician. Sounds like you are a guy with a truck and a ladder.
  • solar_davesolar_dave Solar Expert Posts: 2,395 ✭✭✭✭
    Re: Solar & Subpanel

    It is all in what the permit giver will allow, 40 amp is on the ragged edge of the 20% rule, My code department said they preferred 15%, but the are very conservative.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Solar & Subpanel

    technically you could go up to the 40a + the extra 25a as you've just limited the current incoming from the utility. 40+25=65a.
  • solar_davesolar_dave Solar Expert Posts: 2,395 ✭✭✭✭
    Re: Solar & Subpanel

    Ours was a 200 amp panel with a 175 amp main breaker and a 60 amp solar breaker but the actual inverters only put our about 48 amps combined so our code guy bought off on it.
  • Peter_VPeter_V Solar Expert Posts: 226 ✭✭✭
    Re: Solar & Subpanel
    Jburgess wrote: »
    200 * 1.2 =240 amps max feed

    240 – 200 main = 40 amp max solar feed
    240 – 175 main = 65 amp max solar feed
    240 – 150 main = 90 amp max solar feed

    Can someone explain this rule to me or provide a link?

    If I'm understanding you correctly a 200 amp panel is allowed to have 240 amps worth of breakers? Does this apply if the solar breaker is feeding through the main breaker or ??
    I'm not sure what size panel I have but my main breaker is 100A. My solar feeds into that through a 20 amp breaker but max output from the array is only 12.5 amps currently, but I was thinking I might want to add more panels in the future.

    Thanks.
  • JburgessJburgess Solar Expert Posts: 130 ✭✭✭
    Re: Solar & Subpanel

    From 2008 NEC


    690.64 (B) (2) Bus or Conductor Rating. The sum of the ampere
    ratings of overcurrent devices in circuits supplying power
    to a busbar or conductor shall not exceed 120 percent of the
    rating of the busbar or conductor. In systems with panelboards
    connected in series, the rating of the first overcurrent
    device directly connected to the output of a utilityinteractive
    inverter(s) shall be used in the calculations for
    all busbars and conductors.
  • Peter_VPeter_V Solar Expert Posts: 226 ✭✭✭
    Re: Solar & Subpanel
    Jburgess wrote: »
    From 2008 NEC


    690.64 (B) (2) Bus or Conductor Rating. The sum of the ampere
    ratings of overcurrent devices in circuits supplying power
    to a busbar or conductor shall not exceed 120 percent of the
    rating of the busbar or conductor.


    Thanks, makes sense.

    How do I tell what size panel I have? I think that the company that made (challenger?) it went out of business a while back.
  • JburgessJburgess Solar Expert Posts: 130 ✭✭✭
    Re: Solar & Subpanel
    Peter_V wrote: »
    Thanks, makes sense.

    How do I tell what size panel I have?


    Obviously the best way is the label on the panel. Missing that there are many variables-All-In–One, Split bus, Main breaker, Main lug for a few. A picture of the panel might help. Chances are good if you have a 100 amp main breaker, it is a 100 amp panel.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Solar & Subpanel

    each pv should have a small plate with its ratings on it. with a 100a breaker you most likely have a 100a breaker panel. this can go to as high as 120a on the bus bars and means you can use up to 20a in solar to that properly sized 20a breaker. to go to 30a in solar from pvs for example would mean either using a smaller 90a main breaker (don't think they come in that value) or get a larger main panel that will contain buses that can handle the higher overall currents.

    be careful as the ac amps at 120vac will differ from dc amps at the lower dc voltages before being inverted.
  • Peter_VPeter_V Solar Expert Posts: 226 ✭✭✭
    Re: Solar & Subpanel
    Jburgess wrote: »
    Obviously the best way is the label on the panel. Missing that there are many variables-All-In–One, Split bus, Main breaker, Main lug for a few. A picture of the panel might help. Chances are good if you have a 100 amp main breaker, it is a 100 amp panel.

    Unfortunately the panel does not appear to be labeled. If the label was on the outside, it's been painted over.
    Here is a photo of the outside:
    Meters.jpg

    The meter on the right is the PBI meter for the solar.

    Here is the inside:
    Breakers.jpg

    Gotta love how the "Licensed Electrician" jury rigged the breakers to tie them together huh? And it passed inspection. I finally got around to ordering the proper breaker, or at least one I think is acceptable.
    Cutler hammer is listed as an approved replacement for Challenger and Westinghouse breakers, so I assume that means I can replace a Challenger breaker with a Westinghouse. I'm pretty sure Cutler-Hammer bought out Challenger and I think Westinghouse and Cutler-Hammer are now owned by Eaton?
    Anyway, the one the electrician used is a Simons which is not listed as a replacement for a Challenger even if he did have the proper tied bar installed.

    Anyway, replacing this breaker was what got me thinking about adding CTs to monitor my power (discussed on this thread) I figure while I've got the panel powered down and the breaker out it would be a good time to install a CT on the wires and add a whole house surge suppressor.
  • JburgessJburgess Solar Expert Posts: 130 ✭✭✭
    Re: Solar & Subpanel

    That looks like a 100 amp panel. The labels are usually on the inside of the lid.

    A 90 amp main breaker was suggested. Unfortunately 225.39 (C) requires a 100 amp minimum disconnect. So you are limited to 20 amps solar without upgrading your service.

    225.39 (C) One-Family Dwelling. For a one-family dwelling, the
    feeder disconnecting means shall have a rating of not less
    than 100 amperes, 3-wire.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Solar & Subpanel

    interesting that now the many 60amp service panels out there are now against the rules. i guess trailers and small homes need lots more electric than 60a to be safe. i'm starting to think the nec has gone bonkers.
  • JburgessJburgess Solar Expert Posts: 130 ✭✭✭
    Re: Solar & Subpanel
    niel wrote: »

    i'm starting to think the nec has gone bonkers.

    Perhaps the amendment process has been perverted by special interests. I have not warmed up to the requirements for TR receptacles and Arc-fault breaker, yet.
  • Peter_VPeter_V Solar Expert Posts: 226 ✭✭✭
    Re: Solar & Subpanel
    Jburgess wrote: »
    That looks like a 100 amp panel. The labels are usually on the inside of the lid.
    That's what I figured, thanks. FWIW any label that might have been on the inside of the lid has fallen off long ago.
    A 90 amp main breaker was suggested. Unfortunately 225.39 (C) requires a 100 amp minimum disconnect. So you are limited to 20 amps solar without upgrading your service.

    That's not a problem, my solar breaker is already 20 amps and I'm only using 12.5 of them. I'm assuming the 80% rule still applies? If so I can go up to 16 amps which would be 4 more enphase inverters.
    Of course I'm basing this on maximum output from the Enphase (just shy of 200 watts), not the rated 190 watts. If the calculations are done on rated output, then I can add 5 more inverters/panels.

    As it is I'm already generating surplus power, I've banked over 500 kwh in the last 3 months, so it's not really an issue until I get new batteries for my electric truck.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Solar & Subpanel

    i agree that you can expand a bit more until you wind up being at 20a and 240vac of solar being delivered to the bus and to the grid. 20a from solar + 100a from the grid = 120a total on the bus.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Solar & Subpanel
    solar_dave wrote: »
    Ours was a 200 amp panel with a 175 amp main breaker and a 60 amp solar breaker but the actual inverters only put our about 48 amps combined so our code guy bought off on it.
    1.2 X 200A = 240A. 240A - 175A = 65A. With a 60A breaker you are within the 20% rule. Your code guy was correct, but it wasn't because of the 48A combined inverter output.
  • solar_davesolar_dave Solar Expert Posts: 2,395 ✭✭✭✭
    Re: Solar & Subpanel
    ggunn wrote: »
    1.2 X 200A = 240A. 240A - 175A = 65A. With a 60A breaker you are within the 20% rule. Your code guy was correct, but it wasn't because of the 48A combined inverter output.

    Yep I know but he didn't like it much. They did force a service entrance upgrade from a single 200 amp panel to dual 200 amp panels and a 400 amp meter/transformer line, add $4.3K to the project.

    Really that is not so bad as I was adding a 700 sq ft building on the property with 125 Amp service sub-panel and needed the extra capacity anyway, was nice to get the 30% tax credit on the $4300 from the solar project. Same code guy came back on the building project and nodded his head with no issues.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Solar & Subpanel

    i don't think the upgrade to another breaker panel was warranted, but it goes back to what we often say here in that the inspector can do whatever he pleases and thus make you do things too beyond the call.
  • BatikikikBatikikik Solar Expert Posts: 141 ✭✭✭✭✭
    Re: Solar & Subpanel

    Thank you for posts , they are very useful for everybody .
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