Service Panel Too Small at 200 amps- Help!

Jimsolar
Jimsolar Registered Users Posts: 10 ✭
in Advanced Solar Electric Technical Forum #1
I am new to solar PV. I am doing a self install of a 10.0 kw ac system in the San Diego area. I am installing sixty (60) 200 watt panels, equally split through 2 SMA 6000 inverters. If I combine the two inverters before connecting to my electric panel, then I need a 60 amp breaker in my panel. If I run both AC outputs from the inverters directly into my panel, then I need two 40 amp breakers (one for each). My panel is rated at 200 amps max, and I have a 200 amp main breaker. NEC (and the local inspector) says max breaker size is 120% of the panel minus the main breaker (200 amps x 1.2 = 240 amps minus the 200 amp breaker = 40 amp maximum breaker allowed). So I cannot run my inverters combined because that requires a 60 amp breaker. And in San Diego, they add the sum of all breakers feeding solar into the panel which means running them separately is 40 amps + 40 amps = 80 amps which is also greater than the 40 amps the panel can accommodate. So, I see only two options: 1) upgrade my service panel or 2) downsize my main breaker from 200 amps to 175 amps, which would then allow a 60 amp breaker. But I don't want to downsize it. Do any of you have any other potential solutions? Many thanks in advance!
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  • TnAndy
    TnAndy Solar Expert Posts: 249 ✭✭
    #2
    Re: Service Panel Too Small at 200 amps- Help!

    I can't see where going to a 175 main ( assuming you could even find one ) will help..

    175 x 1.2 = 210 - 175 = 35amp max breaker size ( am I missing something ? )

    Looks like service upgrade time. I had to go to a 400amp main service myself to put in a 2.1kw system that I knew I would expand to a 3.5 eventually.
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  • Jimsolar
    Jimsolar Registered Users Posts: 10 ✭
    #3
    Re: Service Panel Too Small at 200 amps- Help!

    Thanks for the quick reply. The math is actually a little different from your calcs when you downgrade. Remember the service panel capacity is the key:
    200 amps x 1.2 = 240 less 175 amp main breaker = 65 amps available for a breaker.
    So if I downgraded my 200 amp main breaker to 175 amps, then I could indeed accommodate the 60 amp breaker required for the inverters. But of course I'm not wild about downgrading, and don't know how it will affect future electrical loads...
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  • lorelec
    lorelec Solar Expert Posts: 200 ✭✭
    #4
    Re: Service Panel Too Small at 200 amps- Help!

    NEC 690-64(a) allows you to do a "supply side" tap after your meter but before your main 200A breaker:

    "A photovoltaic power source shall be permitted to be connected to the supply side of the service disconnecting means as permitted in Section 230-82(5)."

    I think that normally you would need to install a second enclosure to accomodate the tap (and the additional breakers between inverters and tap), but I suppose you could do it inside of your main service entrance panel. You should probably contact a qualified electrician in your area to confirm.

    Marc
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  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    #5
    Re: Service Panel Too Small at 200 amps- Help!

    You say your rig is a 10kw, but you also say 60 x 200 watt panels, which = 12000w or 12kw.

    According to the SMA 6000 spec sheet, that inverter puts out a max of 25a (at 240v) and if separate, each inverter would need a disconnect rated at 125%, which is 31.25a - so you upsize to the next size breaker for 40a.

    Both inverters combined would put out 50a, of which 125% is 62.5a which would mean combined you would need a 70a breaker - not a 60 as you stated.

    Even using Wiles example of combining in a sub-panel here:

    http://www.homepower.com/view/?file=HP89_pg124_CodeCorner

    It still comes out to more than the 240a supply you are allowed with your panel.

    So yes, as for connecting to the load side...you're stuck - either downgrade the main grid supply breaker or upgrade the panel.


    But, as lorelec mentioned, there is provision in the NEC for connecting utility-interactive inverters via supply side tap. Wiles discusses it here:

    http://www.homepower.com/view/?file=HP112_pg92_CodeCorner
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  • Jimsolar
    Jimsolar Registered Users Posts: 10 ✭
    #6
    Re: Service Panel Too Small at 200 amps- Help!

    Lorelec-

    Wow, that is great news! After reading the Wiles article on supply side connections, it appears that if I tap in (with proper disconnects, etc.) between the electric meter and the service panel main breaker, it doesn't really matter that I have a 10.0 or 12.0 kw size PV system that otherwise would require a 65 amp breaker on the load side, since I guess ultimately the 200 amp main disconnect/breaker will protect my panel... Is this kind of the gist of it?

    Many, many thanks! I was ready to spend about $1,500 to upgrade my panel from 200 amps to 225 amps (going to 400 amp upgrade would have required me to abandon my existing underground 2" conduit from my transformer to my service panel and replace it with 3" conduit-- which would have been impossible). You guys are great!
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #7
    Re: Service Panel Too Small at 200 amps- Help!

    Not sure why your having to upgrade anything but the bus-bars in the panel. The NEC code doesn't require a larger main breaker or service wiring, its only requires that the actual bus-bars can handle the additional local generation in addition to the mains supplied power

    I would think pulling the meter, pull the breakers and then just swap out the bus-bars would be the way to address this. If you look at how a panel is built, its all modular and only requires a few nuts to disassemble, at worst, take the guts out of a 225 panel and swap to your panel.
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  • Pgovetom
    Pgovetom Solar Expert Posts: 30 ✭
    #8
    Re: Service Panel Too Small at 200 amps- Help!

    Upgrading your bus bars is possible or downrating your panel to 150A is also possible to meet the code. John Wiles wrote one of his power articles on this subject.

    http://www.homepower.com/view/?file=HP121_pg112_CodeCorner

    http://www.nmsu.edu/~tdi/pdf-resources/CC111.pdf

    http://www.nmsu.edu/~tdi/pdf-resources/IAEI-3to4-06.pdf

    http://photovoltaics.sandia.gov/docs/PDF/Wiles_113_Final.pdf

    I did the same thing ( two 7000w SB7000US inverters combined in a Squared 6/12 dual 40A combiner with 80A output breaker to fused 80A disconnectr) and ended up doing a line side tap. That means you tie in on the utility side of the main 200A breaker and before the customer side of the meter. That way the current doesn't flow on your bus bars. It does mean you need to feed it from a properly rated fused disconnect switch or something similar.

    I used a Squared D 80 AMP disconnect switch with 80 AMP RK5 limiting fuses and #4 THWN-2 wire in schedule 80 conduit. I have a side by side Squared D 200A service and its ok to attach to the wiring between the meter customer side and 200A service breaker from the properly rated source with utility sized wire remembering the line side tap is tied through the meter to LOTS of AMPACITY source. Its a tricky issue. I verified it with a solar electrician at my supplier and was told over half their systems now are line side taps rather than backfed breakers. Read the first HP112 John Wiles line side tap Code Corner in my first link.
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  • Jimsolar
    Jimsolar Registered Users Posts: 10 ✭
    #9
    Re: Service Panel Too Small at 200 amps- Help!

    Well, after all that great advice about tapping the inverter into the SUPPLY side of the service panel, I checked and found out that my local electric company, San Diego Gas and Electric, will not permit it. They acknowledge that the NEC allows for it, but that they can set superceding rules. So, I guess it is a panel upgrade after all...
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  • lorelec
    lorelec Solar Expert Posts: 200 ✭✭
    #10
    Re: Service Panel Too Small at 200 amps- Help!

    Uggh...bureaucracy at its finest. You should ask them to reference a rule or document. One person's interpretation of the rules may differ from another's, so unless it is clearly spelled out in a written document, then you might have some wiggle room...especially if you're able to work your way up to someone that can actually flex the rules.

    And not that I EVER recommend circumventing the rules :roll:, but sometimes what they don't know won't hurt them. Unfortunately in your case SDG&E would probably have to pop your meter out first before you can make your tap...so there might not be a way around it if they won't budge.

    Marc
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  • Hoonose
    Hoonose Registered Users Posts: 16 ✭
    #11
    Re: Service Panel Too Small at 200 amps- Help!

    I had to upgrade to 300A service when we put in our 10KW system. This included some trenching to the street. The good news is that the cost to me is reduced through the rebates and tax credits.
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  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    #12
    Re: Service Panel Too Small at 200 amps- Help!
    Jimsolar wrote: »
    Well, after all that great advice about tapping the inverter into the SUPPLY side of the service panel, I checked and found out that my local electric company, San Diego Gas and Electric, will not permit it. They acknowledge that the NEC allows for it, but that they can set superceding rules. So, I guess it is a panel upgrade after all...


    Well, there is still the possibility of upgrading the buss bars - though that's a tough row to hoe.

    Some load center enclosures are rated like this: "100a-225a". The manufacturer just uses different sets of internal components but the enclosure is the same for all of them.

    If yours is like that, *and* you can get the 225a internals from the manufacturer, you could probably upgrade the buss bars.

    Otherwise you can probably forget it - if the box isn't rated for 225a, or if the higher rated buss bars are longer (they might be since the code allows more circuits on them), or if you have to completely gut the box and install entirely new internals (Grainger has some kits) - then you'll be better off just swapping up to 400a.
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  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    #13
    Re: Service Panel Too Small at 200 amps- Help!

    What is the current 200 amp panel manufacture and enclosure rating?

    If its Square-D, upgrading the Buss-bars would be cheap and could be done without any wire removal. Pull the meter, pull the breakers wires attached and replace the buss-bars
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  • Pgovetom
    Pgovetom Solar Expert Posts: 30 ✭
    #14
    Re: Service Panel Too Small at 200 amps- Help!

    FYI A tidbit I found

    SAN DIEGO GAS and ELECTRIC–In many cases, customers have a small 100 amp service and want a solar system that is too large for the service. About 20-30 years ago, SDGE recommended that builders use direct burial cable from the transformer to the service. They have now found that the cable is deteriorating and they are losing power into the ground. SDGE doesn’t want to pay for the cost of their mistake. There is a method in the NEC that allows a supply side tap. In this instance, a new meter box would be installed and the service would be tapped to allow for the larger solar array. SDGE, however, now requires that if there is a rewire, the contractor must trench approximately 30″ deep all the way to the pull box or transformer and put in new conduit. This can cost an additional $3000-$4000 or more. Then, SDGE may charge up to $1000 for the priviledge of fixing their mistake. Even though is is really smart on their part, they still get a dunce award.
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  • Pgovetom
    Pgovetom Solar Expert Posts: 30 ✭
    #15
    Re: Service Panel Too Small at 200 amps- Help!

    A helpful line side tap document:

    http://www.spgsolar.com/assets/SPGLeBlancYates.pdf
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  • lorelec
    lorelec Solar Expert Posts: 200 ✭✭
    #16
    Re: Service Panel Too Small at 200 amps- Help!
    Pgovetom wrote: »
    There is a method in the NEC that allows a supply side tap. In this instance, a new meter box would be installed and the service would be tapped to allow for the larger solar array. SDGE, however, now requires that if there is a rewire, the contractor must trench approximately 30″ deep all the way to the pull box or transformer and put in new conduit. This can cost an additional $3000-$4000 or more. Then, SDGE may charge up to $1000 for the priviledge of fixing their mistake.

    I think a new service panel would be a less expensive proposition. But maybe this means that SDG&E is somewhat flexible on the supply-side tap?

    Marc
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  • Pgovetom
    Pgovetom Solar Expert Posts: 30 ✭
    #17
    Re: Service Panel Too Small at 200 amps- Help!

    Solar Guppy said:
    If its Square-D, upgrading the Buss-bars would be cheap and could be done without any wire removal. Pull the meter, pull the breakers wires attached and replace the buss-bars

    All service panels are UL tested with their intended bus bar. Square D explained they run 200A through my combo meter service panel in its UL listing test and verify the bus bar temperature. Unless you are buying a bus bar that is INTENDED for the next higher model and that model is exactly the structure and bus bar Square D UL tested, then just putting a bigger bus bar in any panel will work electrically but will violate the UL listing which will not pass the local building authority final inspection - if its caught. :D

    Any modification to a panel that creates a special variant not explicitly UL tested by the manufacturer and upgrade is supported will trigger a UL listing violation and won't be legal. :grr

    I asked a technical person at Square D about larger bus bars for my panel and he said thy don't offer larger bars for the reason stated and my panel does not have a larger Amperage but identical version where I could upgrade. :confused:

    This bus bar idea is electrically correct but only rarely will you be lucky enough to have upgrade bars available supported by Square D or anyone - or so they told me and it makes sense. :cry:
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  • ALBANYSOLARGUY
    ALBANYSOLARGUY Registered Users Posts: 12 ✭
    #18
    Re: Service Panel Too Small at 200 amps- Help!

    Try this first. Turn on everything in your house and use a clamp meter to see if there's any way to combine lighting loads or convenience receptacles that would eliminate breakers in your loadcenter. If you could eliminate two 20-ampere breakers, I believe you squeak under the wire. Again contact an electrician in your locality to see if this is do-able. Personally, I would do that before I went to a service up-grade. I'm an electrician by trade, and combining the odd-ball lighting loads, attic and basement lights, and single receptacles for stereo, and exterior christmas light receptacles freed up 3 to 4 pole spaces in my loadcenter. Changing the buss-bars in a residential loadcenter will void the warranty, which is limited to begin with. Even though you are doing a self-install, I recommend having the AHJ inspect the finished project. God forbid something should happen, If you can produce a passed inspection certificate the PV array might not be scrutinized by an insurance company as closely. Cover yourself. Insurance companies WILL look at the array if something happens.
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  • ALBANYSOLARGUY
    ALBANYSOLARGUY Registered Users Posts: 12 ✭
    #19
    Re: Service Panel Too Small at 200 amps- Help!

    Also, make sure the grounding is to the letter up to the current enforceable NEC. I have seen too many PV installers not get the grounding right. Look back thru the posts, there are a number of posts on grounding with links by John Wiles. I believe he is the guy who wrote article 690 of the NEC(If not he's the guy who petitions for changes to that section). I would follow his recommendations as best as I could. Don't skimp on costs at the expense of safety.
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  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    #20
    Re: Service Panel Too Small at 200 amps- Help!
    ALBANYSOLARGUY wrote: »
    Try this first. Turn on everything in your house and use a clamp meter to see if there's any way to combine lighting loads or convenience receptacles that would eliminate breakers in your loadcenter. If you could eliminate two 20-ampere breakers, I believe you squeak under the wire.

    That will free up some of the LOAD side, but won't do anything to free up the SUPPLY side.
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  • ALBANYSOLARGUY
    ALBANYSOLARGUY Registered Users Posts: 12 ✭
    #21
    Re: Service Panel Too Small at 200 amps- Help!

    Section
    690.64(B)(2) allows an exception to the general rule.The exception allows the sum of all overcurrent devices
    connected to a circuit, load center, or feeder to exceed the rating of that circuit by 20 percent. The way I see that is, if some of the existing overcurrent devices could be eliminated, their value is not figured in the overall calculation. With the elimination of 2-20 ampere circuits(one on each phase) you have theoretically lowered the total load by 20 amps. The actual value of the load is meaningless. It could be 2 or it could be 16 amps. The value of the breaker is what is counted. How do you see it?
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  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    #22
    Re: Service Panel Too Small at 200 amps- Help!
    ALBANYSOLARGUY wrote: »
    Section
    690.64(B)(2) allows an exception to the general rule.The exception allows the sum of all overcurrent devices
    connected to a circuit, load center, or feeder to exceed the rating of that circuit by 20 percent. The way I see that is, if some of the existing overcurrent devices could be eliminated, their value is not figured in the overall calculation. With the elimination of 2-20 ampere circuits(one on each phase) you have theoretically lowered the total load by 20 amps. The actual value of the load is meaningless. It could be 2 or it could be 16 amps. The value of the breaker is what is counted. How do you see it?

    There is a difference between load and supply when referring to the breakers on a buss.

    LOAD breakers (exception only applies to residential) are allowed to exceed panel rating by 25%.

    SUPPLY breakers (exception only applies to residential) are allowed to exceed panel rating by 20%.


    The problem the OP has is that he needs to connect more than 40a to the SUPPLY. He has a 200a panel, and to connect his entire solar supply would exceed 240a (200a X 120%).

    NOTHING that he does to reduce the number of LOAD breakers will change the SUPPLY side calcs - he has a 200a main breaker in there now, he can add NO MORE THAN another 40a supply to that panel (unless that panel is actually rated at 225a but only has a 200a main breaker - then he could get away with it).

    Even if he only has a single 15a LOAD breaker in that panel - he still can't exceed 240a on the SUPPLY side.


    (EDIT: BTW, I'm a journeyman with over 24,000 hours of high voltage and about 8,000 hours of VDV experience - and a rank amateur when it comes to solar...but I'm learning.)
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  • ALBANYSOLARGUY
    ALBANYSOLARGUY Registered Users Posts: 12 ✭
    #23
    Re: Service Panel Too Small at 200 amps- Help!

    You're absolutely right. My bad. I had to go back and read the whole thread.(which I should have done anyway) It seems almost as if purchasing a panel with 225 amp mains and a 200 amp main breaker is the way to go. My local utility will only let you add a smaller service(100 ampere) with its own meter. It is an absolute hassle to get approval for a residential upgrade over 200 amperes for a single dwelling. I, too am a JW. 23 years in the local, also a rank amateur for solar, and I just learned something. Thanks. Going to work. I'll check the thread later.
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