Back feed circuit breaker

System
System Posts: 2,511 admin
in PV Installers Forum - NEC, Wiring, Installation #1
I am planning on installing a 8 kw Grid Tied PV system. The building inspector (in Virginia) is requiring a back feed breaker in the main panel. Is this something new in the code? I haven't had it come up before.
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  • Jburgess
    Jburgess Solar Expert Posts: 130 ✭✭✭
    #2
    Re: Back feed circuit breaker

    In the 2011 code: 690.10 (E)

    (E) Back-fed Circuit Breakers. Plug-in type back-fed circuit
    breakers connected to a stand-alone inverter output in
    either stand-alone or utility-interactive systems shall be secured
    in accordance with 408.36(D). Circuit breakers that
    are marked “line” and “load” shall not be backfed.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,714 admin
    #3
    Re: Back feed circuit breaker

    There are two "Back Feed" requirements that I am aware of...

    One is a fuse or breaker to prevent back feed into the solar array. An older requirement and one that my vendor got around by an engineering statement from the manufacturer that stated it will not back feed the solar panels at any time.

    The second is what Jburgess posted. That is every GT inverter must have a branch circuit breaker from the main panel that is rated for the gauge wire used (i.e., 14 awg wire is 15 amp breaker, 12 awg is 20 amp, 10 awg is 30 amp, etc.).

    And some breakers are marked "Line" and "Load" on their connections--those breakers cannot be back feed or it will violate their UL Listing.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #4
    Re: Back feed circuit breaker
    Jburgess wrote: »
    In the 2011 code: 690.10 (E)

    (E) Back-fed Circuit Breakers. Plug-in type back-fed circuit
    breakers connected to a stand-alone inverter output in
    either stand-alone or utility-interactive systems shall be secured
    in accordance with 408.36(D). Circuit breakers that
    are marked “line” and “load” shall not be backfed.
    But that does not mean that they have to be secured with the extra fasteners that 408.36(D) requires. 705.12(D)(6) (referred to by 690.64, which was where this language was in the NEC200eight) grants an exception for listed utility-interactive inverters. I assume that this is because of UL1741 which requires that utility-interactive inverters shut off when they no longer "see" grid voltage on their outputs, so if you pull the breaker even under load all its terminals will be de-energized.
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  • Jburgess
    Jburgess Solar Expert Posts: 130 ✭✭✭
    #5
    Re: Back feed circuit breaker

    That exception was eliminated in the 2011 code.

    Here's 690.64 in the 2011 code:

    690.64 Point of Connection. Point of connection shall be
    in accordance with 705.12.
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #6
    Re: Back feed circuit breaker
    Jburgess wrote: »
    That exception was eliminated in the 2011 code.

    Here's 690.64 in the 2011 code:

    690.64 Point of Connection. Point of connection shall be
    in accordance with 705.12.
    It wasn't eliminated, just moved. 705.12(D)(6) Fastening. says: "Listed plug-in type circuit breakers backfed from utility-interactive inverters that are listed and identified as interactive shall be permitted to omit the additional fasteners normally required by 408.36(D) for such applications." This is virtually verbatim what 690.64(B)(6) said in NEC2008, but in NEC2011, 690.64 simply points to 705.12, which says the same thing.
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  • Jburgess
    Jburgess Solar Expert Posts: 130 ✭✭✭
    #7
    Re: Back feed circuit breaker

    Good to know. Thanks.
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