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FEEDERS TAP RULES VS EQUIPMENT GROUND 250.122(G)

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    FEEDERS TAP RULES VS EQUIPMENT GROUND 250.122(G)

    we installing new meter pan for a cable company at Manhattan, some times we tap at the end line box, copper detail, and if we have already six main disconnects we tap of the load side of any existing main disconnect as as secondary disconnect using the tap rules, 10ft from the tap and 10% minimum of the wire, example: from the OCPD is 800A on the main disconnect the 10% is 80A so we using #4 THHN for the tap conductors and because is NYC we use #6 THHN for the EGC. the inspector fail my site because the EGC is no rated for 800A on the 250.122 table that is a 1/0 but if i go by the tap rules my site of the tap feeders is correct but if i install 1/0 EGC we will fail inspection because the EGC can no be bigger than my feeders and in 250.122(g). so my question is what size EGC do I have to use because is a very confusing language in the NEC.

    Thanks

    Luis Astudillo
    Construction manager
    L.E.C.I.

    #2
    The size of the egc is based on the OCPD protecting the circuit. For a tap, the conductors are sized to the OCPD.
    Hard to follow your post.
    what size is feeder that is tapped
    what size are the tap conductors
    What is the OCPD of the tap
    What size is the tap EGC
    Are you using the ten ft tap rule?
    Last edited by charlie b; 10-22-19, 04:10 PM.
    Moderator-Washington State
    Ancora Imparo

    Comment


      #3
      Your OCPD is 800 amps so using the 10' tap rule (10%) your tap conductors must be at least 80 amps. Your EGC with the tap conductors is sized according to the 800 amp OCPD but the EGC is not required to be larger than the tap conductors which are #4. Also nothing says that an EGC cannot be larger than the minimum size required.

      250.122 Size of Equipment Grounding Conductors.
      (A) General. Copper, aluminum, or copper-clad aluminum
      equipment grounding conductors of the wire type shall not be
      smaller than shown in Table 250.122, but in no case shall they
      be required to be larger than the circuit conductors supplying
      the equipment
      .
      Rob

      Moderator

      All responses based on the 2017 NEC unless otherwise noted

      Comment


        #4
        I agree with infinity, EGC does not need to be larger than the ungrounded conductors. Also nothing prohibits it from being larger than the ungrounded conductors, just not required to be larger.
        I live for today, I'm just a day behind.

        Comment

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