125A Load Center, what are my options?

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Valdemar
Valdemar Registered Users Posts: 10
I'm thinking to add solar to my home but my utility company will only allow upgrading to a 125A service panel which is the max that the feed cables can handle. The home has a direct burial feed which can in theory be upgraded but without going into much details let's say it is going to add a significant cost to the project which I'm trying to avoid for obvious reasons. Considering the 120% rule I can only install a ~4Kw array on a 125A panel which will be somewhat undersized for the 2300+ sq. foot home with a pool and an EV to charge daily. I see there are load centers available with side tap which allow to connect solar before the main breaker, but the smallest capacity I can find is 200A. Utility company won't allow to install a 125A main breaker on a 200A panel, their argument is that a future owner can swap the breaker and melt the cables underground. Do 125A load centers with a side-tap exist? Any other options I can consider? Thanks.

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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
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    Re: 125A Load Center, what are my options?

    Welcome to the forum.

    Okay, let's take a look at this.
    You have a 125 Amp service? How new is it? There may be a chance that the bus bars inside are 150 Amp, which give a little bit more room. Otherwise you are limited to a 25 Amp back-feed (no such breaker) or 4800 Watts.

    Now you say that's small for your house with 2300 sq. ft., a pool, and an EV to charge. None of that is relevant to the back-feed as it is all running off that 125 Amp service. The only thing the GT solar will do is reduce the amount of kW hours pulled from the utility; the loads don't care where the power comes from.

    Option #2 is a line-side feed, which may be allowed and would greatly increase the array size. But your utility is arguing against this as they fear someone may put in full 200 Amp service and over-load the underground wires from too much back-feed power. Of course this is also true of the service panel back-feed: someone could put a 200 Amp main breaker in their and up the back-feed to 40 Amps - which would not overload the wires - or 100 Amps or anything else. If people are going to mess up the wiring that's what will happen.

    I'd be wondering what sort of El Cheapo wiring is feeding that house, as the wires from the transformer ought to be able to take much more than the 125 Amp main breaker max. And yes I can see where digging up the wire would be really expensive. But frankly the service is pretty bad and maybe those wires need replacing anyway. Your EV & pool aren't exactly low power users.

    There are several installers on the forum. Let's hear some ideas from them. :D
  • jaggedben
    jaggedben Solar Expert Posts: 230 ✭✭
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    Re: 125A Load Center, what are my options?
    Valdemar wrote: »
    ... I see there are load centers available with side tap which allow to connect solar before the main breaker, but the smallest capacity I can find is 200A.

    There are other ways to do a line side tap (proper term: "supply side connection"), besides a pre-configured load center. There are some meter sockets available with two sets of lugs. Or you could splice in a junction box using something like polaris connectors.

    How about one of these methods to a 100A rated fused disconnect for the solar? With whatever size fuses are appropriate for the output.

    Your jurisdiction shouldn't have a problem with supply side connections, (unless they are one of those jurisdictions that ignores that the NEC permits them).
    Utility company won't allow to install a 125A main breaker on a 200A panel, their argument is that a future owner can swap the breaker and melt the cables underground.

    You might point out that a future owner could do an illegal upgrade of the service panel, anyway. Dangerous, stupid, illegal, but still possible to do. So this is kind of a limited argument from them. But to the extent it's valid, a fused disco with a rating not above 125A should discourage such behavior.
    Option #2 is a line-side feed, which may be allowed and would greatly increase the array size. But your utility is arguing against this as they fear someone may put in full 200 Amp service and over-load the underground wires from too much back-feed power.

    I don't see where he said his utility is objecting to a supply side connection. As long as the back-feed can't exceed the service rating it should be allowed (And this could be discouraged by limiting the rating of the equipment, as mentioned above.)
  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
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    Re: 125A Load Center, what are my options?

    As long as the conduit that is buried is adequate perhaps they will allow a new pull from the transformer. Mine did a upgrade from 200 amp to 400 amp including the wire for about 65 feet for only $300. The large cost was the service entrance upgrade to dual 200 amp boxes. that was $4000.
  • Valdemar
    Valdemar Registered Users Posts: 10
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    Re: 125A Load Center, what are my options?
    solar_dave wrote: »
    As long as the conduit that is buried is adequate perhaps they will allow a new pull from the transformer. Mine did a upgrade from 200 amp to 400 amp including the wire for about 65 feet for only $300. The large cost was the service entrance upgrade to dual 200 amp boxes. that was $4000.

    As far as I understand there is no conduit, it is a direct burial feed.
  • Valdemar
    Valdemar Registered Users Posts: 10
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    Re: 125A Load Center, what are my options?
    Welcome to the forum.

    Okay, let's take a look at this.
    You have a 125 Amp service? How new is it? There may be a chance that the bus bars inside are 150 Amp, which give a little bit more room. Otherwise you are limited to a 25 Amp back-feed (no such breaker) or 4800 Watts.

    Now you say that's small for your house with 2300 sq. ft., a pool, and an EV to charge. None of that is relevant to the back-feed as it is all running off that 125 Amp service. The only thing the GT solar will do is reduce the amount of kW hours pulled from the utility; the loads don't care where the power comes from.

    Option #2 is a line-side feed, which may be allowed and would greatly increase the array size. But your utility is arguing against this as they fear someone may put in full 200 Amp service and over-load the underground wires from too much back-feed power. Of course this is also true of the service panel back-feed: someone could put a 200 Amp main breaker in their and up the back-feed to 40 Amps - which would not overload the wires - or 100 Amps or anything else. If people are going to mess up the wiring that's what will happen.

    I'd be wondering what sort of El Cheapo wiring is feeding that house, as the wires from the transformer ought to be able to take much more than the 125 Amp main breaker max. And yes I can see where digging up the wire would be really expensive. But frankly the service is pretty bad and maybe those wires need replacing anyway. Your EV & pool aren't exactly low power users.

    There are several installers on the forum. Let's hear some ideas from them. :D

    100A service currently. Old POS Zinsco panel which will have to go if I add solar, as far as I understand anyway. Side-feed is okay I think. The problem is that there are no 125A panels that support side-feed by design.
  • Valdemar
    Valdemar Registered Users Posts: 10
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    Re: 125A Load Center, what are my options?
    jaggedben wrote: »
    There are other ways to do a line side tap (proper term: "supply side connection"), besides a pre-configured load center. There are some meter sockets available with two sets of lugs. Or you could splice in a junction box using something like polaris connectors.

    How about one of these methods to a 100A rated fused disconnect for the solar? With whatever size fuses are appropriate for the output.

    Your jurisdiction shouldn't have a problem with supply side connections, (unless they are one of those jurisdictions that ignores that the NEC permits them).



    You might point out that a future owner could do an illegal upgrade of the service panel, anyway. Dangerous, stupid, illegal, but still possible to do. So this is kind of a limited argument from them. But to the extent it's valid, a fused disco with a rating not above 125A should discourage such behavior.



    I don't see where he said his utility is objecting to a supply side connection. As long as the back-feed can't exceed the service rating it should be allowed (And this could be discouraged by limiting the rating of the equipment, as mentioned above.)

    Thanks, I'll look into these other ways. One problem is my panel is flush mounted and the new one will have to be as well, this may limit my options. It is very difficult to argue with the utility company, they just have their set of rules that they follow.

    How is the power of solar array is calculated? Say I install a 125A panel with 100A breaker, as far as I understand this will give me 50A for solar back feed according to the 120% rule, how much kW of solar does 50A translate to, 50A*240V=12kW, or less?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,497 admin
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    Re: 125A Load Center, what are my options?

    The calculations for a 50 amp circuit:

    50 amps * 0.80 NEC derating = 40 amps maximum continuous

    40 amps * 240 volts = 9,600 Watt maximum GT inverter rating....

    Note: You need to look at the output current rating... 40 amps maximum (depends on what voltage they rate the GT inverter at to get rated power).

    The "cost effective maximum solar array would be (roughly):

    9,600 watts * 1/0.77 panel+GT derating = 12,468 Watt "maximum cost effective" array

    It is the maximum output ampere rating that you are looking for (40 amp) here.

    If you look at this Schneider data sheet--The 5kW GT inverter has a 21 amp rated output (and 30 amp circuit breaker rating)--So 10kW would be 42 amps--too high of current for a 50 amp branch circuit per NEC.

    Working backwards:

    5,000 watts / 21 amps = 238 volts "nominal" -- pretty close to 240 VAC I used above.

    40 amps * 238 volts = 9,520 watts of GT inverter for use on a 50 amp branch circuit.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
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    Re: 125A Load Center, what are my options?
    ... you are limited to a 25 Amp back-feed (no such breaker)...

    Just to pick a nit, according to the NEC, 25A is a standard OCPD size.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
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    Re: 125A Load Center, what are my options?
    ggunn wrote: »
    Just to pick a nit, according to the NEC, 25A is a standard OCPD size.

    Really? Must be an American thing. :p
  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
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    Re: 125A Load Center, what are my options?

    You can install any size breaker box you desire as long as the main breaker does not exceed grid entry service rating.

    For example, you rewire in a new panel of 200 amp rating with 100 amp main breaker you could back feed up to 100 amps solar.

    The 120% rule applies to panel bus bars. If max solar generation plus max grid service entrance breaker is added together it cannot exceed 120% of panel bus rating.

    The power company should have no say is size of panel, only entrance breaker. To their argument, there is nothing stopping you or someone else putting a 200 amp main breaker in your 125 amp rated box exceeding the service rating. You usually have to have a licensed electrician to pull meter, which is usually required to change main breaker (unless you also have an outside disconnect switch).
  • jaggedben
    jaggedben Solar Expert Posts: 230 ✭✭
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    Re: 125A Load Center, what are my options?
    RCinFLA wrote: »
    The power company should have no say is size of panel, only entrance breaker.

    I would tend to agree with that, per the NEC. As long as the AHJ signs off it should be okay. But it may depend on the law in Valdemar's area. And/or it may not be worth the fight.
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
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    Re: 125A Load Center, what are my options?
    RCinFLA wrote: »
    For example, you rewire in a new panel of 200 amp rating with 100 amp main breaker you could back feed up to 100 amps solar.

    The 120% rule applies to panel bus bars. If max solar generation plus max grid service entrance breaker is added together it cannot exceed 120% of panel bus rating.
    You could actually backfeed up to 140A into the panel (with 40A or more going to local loads.) You just could not push more than 100A back to POCO. Without any qualifiers, the term backfeed can be ambiguous here.
    SMA SB 3000, old BP panels.
  • Valdemar
    Valdemar Registered Users Posts: 10
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    Re: 125A Load Center, what are my options?
    jaggedben wrote: »
    I would tend to agree with that, per the NEC. As long as the AHJ signs off it should be okay. But it may depend on the law in Valdemar's area. And/or it may not be worth the fight.

    I'm in Los Angeles region and the utility is SoCal Edison, they said they won't approve a 200A panel with a 125A breaker, it was pretty clear. They are a private company, is there even a way I can fight them?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,497 admin
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    Re: 125A Load Center, what are my options?

    If the AHJ (i.e., local building department/inspector) will sign off on the installation--There is not really much they can do other than be obstinate (which is always a possibility).

    You can try for the panel upgrade "this month" and don't even discuss solar until the project is done and you are connected up.

    They can force a utility engineer to evaluate your loads and the capacity of the local distribution system--But I don't see how they can say much if the old/new breaker is still 125 Amps.

    You just tell them you are adding some more branch circuits for LED ceiling lighting--and need more breaker locations... For commercial code, the NEC did not allow you to add more branch breakers than panel bus bar rating... However, I don't think that rule applies to homes (that was "older NEC", newer NEC maybe different).

    -Bill "no NEC expert here" B.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Valdemar
    Valdemar Registered Users Posts: 10
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    Re: 125A Load Center, what are my options?
    BB. wrote: »
    You can try for the panel upgrade "this month" and don't even discuss solar until the project is done and you are connected up.

    Solar was not even brought up specifically, we just asked if we can add a 200A panel with a de-rated MB, and they said no. I'll see if I can go anywhere by getting an approval from the AHJ first. What a pain...
  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
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    Re: 125A Load Center, what are my options?

    One caveat to not putting it in the solar project plan is the panel upgrade may not be used for part of the Federal tax deduction. It has to be part of that project to qualify technically.

    BTW just my opinion that maybe this is another way the Utility might limit the implementation of solar like they seem to be doing lately.