Backfed breaker or Line side tap?

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  • rollandelliott
    rollandelliott Solar Expert Posts: 834 ✭✭
    #32
    Re: Backfed breaker or Line side tap?

    How do you know if you need a service feed upgrade from the transformer?

    I live in a subdivision built in 1995 and all the wires are buried underground.

    I currently have a full 100amp panel. If I upgrade to a 200amp outside load center will I have to have the power company do something else? in order words is the wire going to my house capable of delivering 200amps?
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  • drees
    drees Solar Expert Posts: 482 ✭✭✭
    #33
    Re: Backfed breaker or Line side tap?
    rollandelliott wrote: »
    How do you know if you need a service feed upgrade from the transformer?

    I live in a subdivision built in 1995 and all the wires are buried underground.

    I currently have a full 100amp panel. If I upgrade to a 200amp outside load center will I have to have the power company do something else? in order words is the wire going to my house capable of delivering 200amps?
    Your utility should have records of what kind of wire is currently in the ground and what it's rated for. They also should know what kind of conduit is in the ground. Based on that, they'll be able to tell you what the existing wire is rated for and if it's not sufficient for 200A and whether or not the conduit is sufficient for pulling new wire.

    At least in my experience (my house), I have 100A service, and I think the wire is good for 125-150A (don't remember exactly). And the conduit is not up to current codes, so new conduit would need to be run. This means digging a 30ft long 18" deep trench from my main service panel to the utility hand-hole. The quote I got for doing this was crazy expensive.

    IMO, the best solution in this case (where I don't actually need 200A service, but need the bigger panel if I want to add more PV) is to upgrade the panel to a 200A panel and size the main breaker for whatever the wire is rated for. This gets you as much room for as much PV as you'd ever want to add, and if you really do need/want 200A service down the road, you can dig the trench and pull new wire then.
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  • rollandelliott
    rollandelliott Solar Expert Posts: 834 ✭✭
    #34
    Re: Backfed breaker or Line side tap?

    So I would just take out the preinstalled 200amp breaker and replace it with a 100amp breaker and be able to add up to 140amps of solar power?

    which is probably around 20KW! More than I would ever install.
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  • drees
    drees Solar Expert Posts: 482 ✭✭✭
    #35
    Re: Backfed breaker or Line side tap?
    rollandelliott wrote: »
    So I would just take out the preinstalled 200amp breaker and replace it with a 100amp breaker and be able to add up to 140amps of solar power?
    Yep - that's all you need to do!
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #36
    Re: Backfed breaker or Line side tap?
    rollandelliott wrote: »
    So I would just take out the preinstalled 200amp breaker and replace it with a 100amp breaker and be able to add up to 140amps of solar power?

    which is probably around 20KW! More than I would ever install.
    Well, yes, but understand that when you do that, you reduce by half the amount of power that your house can pull from the grid.
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #37
    Re: Backfed breaker or Line side tap?
    ggunn wrote: »
    Well, yes, but understand that when you do that, you reduce by half the amount of power that your house can pull from the grid.


    I think the point was he only has a 100 amp service now. This was to allow a decent backfeed percentage on the panel.
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #38
    Re: Backfed breaker or Line side tap?
    solar_dave wrote: »
    I think the point was he only has a 100 amp service now. This was to allow a decent backfeed percentage on the panel.
    I understood about the expanded headroom for the PV. So I guess he wants to replace his 100A panel with a 200A panel and swap out the main breaker for a 100A breaker. Yes, I see that now. Never mind.
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  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    #39
    Re: Backfed breaker or Line side tap?

    Make sure the inspector and the utility co. will sign off on it before you do it.

    If there is a chance someone could come along later and swap out the 100a breaker for a 200a - but the feed wire isn't rated for 200a...

    It's likely they won't even allow an upgrade to a 200a panel unless the feed is wire is also upgraded.

    THEN, of course, you can install a 100a main breaker if you want.
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  • drees
    drees Solar Expert Posts: 482 ✭✭✭
    #40
    Re: Backfed breaker or Line side tap?
    dwh wrote: »
    If there is a chance someone could come along later and swap out the 100a breaker for a 200a - but the feed wire isn't rated for 200a...
    Isn't that the case for ANY circuit breaker?
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