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  • 200 Amp Center-Fed Service Panel Options?

    Hello to everyone on this forum. I've been lurking for a while, but finally joined today. I'm planning to add a 8.8kW, grid-tied PV system to my roof here in San Diego hopefully before the summer heat arrives! I've had a few vendors out, but eventually decided to do the system as owner/builder primarily because of cost, but also because I want the job to be really clean without a lot of conduit showing.

    My dilemma is my service panel. It's a 200 amp Square D panel, but it's center-fed which is a bummer.

    Here are what I understand my options to be:

    1) Do a load calc and possibly drop the main to 150 amps. (I believe I'd be adding a 40 amp PV breaker, so I don't think a 175 amp main will work?)

    2) New larger service panel. (I've actually done a couple of them, but with the stucco it's not my favorite solution.)

    3) The SDG&E gizmo that I don't completely understand, and sounds very expensive.

    Have I missed some elegant and easy solution?

    Thanks,
    Mike

  • #2
    Supply side tap.
    OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

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    • #3
      The Renewable Meter Adapter is SDG&E's version of a line side tap. For the $1400 another forum member indicated, it doesn't sound like a bad option for you. One thing you might want to ask them about is lead-time on the RMA installation... if you end up doing a service panel upgrade, you should expect it to add at least another month to the project timeline.
      CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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      • #4
        Wow, the SDG&E Renewable Meter Adapter sounds like it might be a good solution! On SDG&E's website, they have a picture of one installed. It's not super attractive, but it sure might solve my problem. $1,400 is a lot more than I could do a service panel upgrade for, but I really don't want to break out my stucco...it never matches correctly. Thanks for all the great info!

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        • #5
          What size is your inverter? You can go up to a 7.7kW inverter (SMA or SolarEdge) on a 200A panel using a 40A breaker. As long as it is at the end of the buss with as many branch circuits in between the main and backfeed breaker as possible, it will meet code. There might be some inspectors that will hassle this but the code experts I've learned from say it is OK to use center-fed busses.
          BSEE, R11, NABCEP, Chevy BoltEV, >3000kW installed

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          • #6
            Originally posted by solarix View Post
            What size is your inverter? You can go up to a 7.7kW inverter (SMA or SolarEdge) on a 200A panel using a 40A breaker. As long as it is at the end of the buss with as many branch circuits in between the main and backfeed breaker as possible, it will meet code. There might be some inspectors that will hassle this but the code experts I've learned from say it is OK to use center-fed busses.
            I agree that from a current-flow standpoint, it would be fine to put the heavy loads (2-40amp a/c's and a 100 amp subpanel for pool/patio) between the main and the backfeed. But will an inspector sign off on it based on that? Would the proposed breaker configuration be part of my permit application? If I could do this, it would save me $1,400 skipping the RMA device.

            BTW-I'm still drawing up my system. My thought was to start another thread once I get this service panel issue figured out. But quickly here's where I'm at right now...

            I can get 275 watt LG panels and Enphase M250's for a really good price (my buddy is a contractor), so that's what I was going to start with. Ideally 32 panels for 8.8kW, but my best roof plane seems to only allow for 28-29 panels, tightly. I could possibly step up to 305 watt panels. I just know that 275 seems to be the sweet spot for pricing. I'm still trying to figure it out.

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            • #7
              Originally posted by 71SoCal View Post
              I agree that from a current-flow standpoint, it would be fine to put the heavy loads (2-40amp a/c's and a 100 amp subpanel for pool/patio) between the main and the backfeed. But will an inspector sign off on it based on that? Would the proposed breaker configuration be part of my permit application? If I could do this, it would save me $1,400 skipping the RMA device.

              BTW-I'm still drawing up my system. My thought was to start another thread once I get this service panel issue figured out. But quickly here's where I'm at right now...

              I can get 275 watt LG panels and Enphase M250's for a really good price (my buddy is a contractor), so that's what I was going to start with. Ideally 32 panels for 8.8kW, but my best roof plane seems to only allow for 28-29 panels, tightly. I could possibly step up to 305 watt panels. I just know that 275 seems to be the sweet spot for pricing. I'm still trying to figure it out.
              On roof space, don't forget to account for the fire setbacks or get a variance. Just sayin'.

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              • #8
                Code doesn't address center-fed busses, just that the backfed breakers need to be at the end of the buss. So it falls to the judgement of the inspector. As long as you have some serious loads in between the Main and the solar breaker, you are complying with the intent of the code and should be ok.
                BSEE, R11, NABCEP, Chevy BoltEV, >3000kW installed

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                • #9
                  Originally posted by J.P.M. View Post
                  On roof space, don't forget to account for the fire setbacks or get a variance. Just sayin'.
                  Yes, good call! There is a 36" "Calfire" setback from the edges, ridges, hips and valleys. It's a lot of good solar real estate that is untouchable.

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                  • #10
                    Originally posted by 71SoCal View Post
                    Yes, good call! There is a 36" "Calfire" setback from the edges, ridges, hips and valleys. It's a lot of good solar real estate that is untouchable.
                    There are exceptions or appeals possible. See the Calfire regs. One poster here, (in Poway if my memory serves) actually followed the S.O.P. and claims to have received an exemption from the fire marshal/rep.

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                    • #11
                      Originally posted by 71SoCal View Post
                      Yes, good call! There is a 36" "Calfire" setback from the edges, ridges, hips and valleys. It's a lot of good solar real estate that is untouchable.
                      "Calfire" setbacks are 36" from ridge and edge, 18" from center of Hips and center of valley.

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                      • #12
                        Originally posted by solarix View Post
                        Code doesn't address center-fed busses, just that the backfed breakers need to be at the end of the buss. So it falls to the judgement of the inspector. As long as you have some serious loads in between the Main and the solar breaker, you are complying with the intent of the code and should be ok.
                        The statement of the 120% rule in the NEC is specifically associated with the backfed breaker being at the opposite end of the bus from the main, not just at one end.
                        When the main is in the center rather than at one end, every AHJ I have heard of has stated that the 120% rule does not apply for that reason.
                        Unless the panelboard is rated not less than the sum of the ampere ratings of all overcurrent devices supplying it, a connection in a panelboard shall be positioned at the opposite (load) end from the input feeder location or main circuit location.
                        SunnyBoy 3000 US, 18 BP Solar 175B panels.

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                        • #13
                          Originally posted by J.P.M. View Post
                          There are exceptions or appeals possible. See the Calfire regs. One poster here, (in Poway if my memory serves) actually followed the S.O.P. and claims to have received an exemption from the fire marshal/rep.
                          Wish I knew how to get an exemption from the fire marshal on the setback from the ridge. I don't have enough roof space to eliminate my electrical bill completely.

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                          • #14
                            Originally posted by jsquared22 View Post
                            Wish I knew how to get an exemption from the fire marshal on the setback from the ridge. I don't have enough roof space to eliminate my electrical bill completely.
                            I have seen reports of success on exemption from the ridge setback on one half of the roof when the attic is one contiguous space and there is good access to ventilate the attic from the other side of the ridge.
                            SunnyBoy 3000 US, 18 BP Solar 175B panels.

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                            • #15
                              So I went down to the City of San Diego’s Development Services Department to ask about my center-fed service panel issue. The inspector told me that they will absolutely NOT approve a PV back-feed on a center-fed panel if the sum of the main and the back-feed breaker exceed the bus rating, which is 200 amps in my case.

                              He told me that my options are as follows:

                              1) Replace the service panel to a higher bus rating, or with an end-fed main. (Even with an end-fed main and the 120% rule, my PV breaker might exceed that number).

                              2) De-rate the main breaker sufficiently. This would need to be signed off by a PE. (I don’t like this option anyway since my two a/c’s, pool pumps and oven alone draw over 120 amps).

                              3) Use the SDG&E RMA supply-side tap.

                              So with that, I’m thinking that the RMA tap seems like my best option. It seems easy (SDG&E does the work), and from the city’s perspective, my service panel is original and therefore doesn’t require any consideration beyond approving the RMA device. It will cost $1,326, but after the 30% federal credit, it comes out to $928.

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