Is a subpanel feed tap allowed?

theenergyguy
theenergyguy Registered Users Posts: 12 ✭✭
in PV Installers Forum - NEC, Wiring, Installation #1
We have a situation where we want to tie a 7kW inverter into a 125amp subpanel that's fed by a 200 amp main panel. The ampacity of the wire feeding the sub is sufficient but the sub isn't.

While we can upgrade the sub to 200 amp to get the necessary busbar rating, I'm wondering if anyone has done a subpanel feed tap. Seems logical - similar to a line-feed tap off a main panel, we just wouldn't need to call the utility to turn off the power as we would in a main panel feed tap because we have the subpanel breaker in the main panel we can shut down to tap the sub.
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  • drees
    drees Solar Expert Posts: 482 ✭✭✭
    #2
    Re: Is a subpanel feed tap allowed?

    So I take it you'd use that tap to feed another sub-panel with a 40A breaker to feed the inverter? If so, that should be OK, but your local inspector will be able to confirm.
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  • theenergyguy
    theenergyguy Registered Users Posts: 12 ✭✭
    #3
    Re: Is a subpanel feed tap allowed?

    My first thought was to splice into the subpanel feed with a tap - our electrician suggests a gutter box be the splice point - and use a 40 amp AC disconnect between the inverter feed and the tap (less cost than a subpanel).....but I'm open to other suggestions!

    We've got a similar issue on jobs with 3-phase (one @ 208, one @ 277) where the panels (no larger than 225 amp) won't support the three inverters we want to use on each phase (inverters varying from 4kW to 7kW)......I'd love suggestions on the most cost-effective way to power these 3-phase panels as well!
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  • drees
    drees Solar Expert Posts: 482 ✭✭✭
    #4
    Re: Is a subpanel feed tap allowed?
    theenergyguy wrote: »
    My first thought was to splice into the subpanel feed with a tap - our electrician suggests a gutter box be the splice point - and use a 40 amp AC disconnect between the inverter feed and the tap (less cost than a subpanel).....but I'm open to other suggestions!
    That should work...
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  • Philip C
    Philip C Solar Expert Posts: 45 ✭
    #5
    Re: Is a subpanel feed tap allowed?

    How is the sub panel fed? If fed by a breaker from the main that is less than 100A then I wouldn't see an issue with back-feeding the sub with a 40A breaker.

    Long as we follow the 120% rule
    125A * 1.2 = 150A
    The sum of all power feeding breakers can not exceed 150A.
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