Code Q&A: Grounding and Bonding for Remote Building

A. Each building/structure's disconnect must be connected to an electrode of a type identified in 250.52 [250.32(A)]. A grounding electrode isn't required where the building/structure is served with a 2-wire, 3-wire, or 4-wire multiwire branch circuit [250.32(A) Ex].The grounding electrode conductor must terminate to the grounding terminal of the disconnecting means, and it must be sized in accordance with 250.66, based on the conductor area of the ungrounded feeder conductor [250.32(E)].

Notes:

•  The grounding of the building/structure disconnecting means to the earth is intended to help in limiting induced voltages on the metal parts from nearby lightning strikes [250.4(A)(1)].

•  The Code prohibits the use of the earth to serve as an effective ground-fault current path [250.4(A)(5) and 250.4(B)(4)].

•  If the grounding electrode conductor is connected to a ground rod, the portion of the conductor that’s the sole connection to the ground rod isn’t required to be larger than 6 AWG copper [250.66(A)]. If the grounding electrode conductor is connected to a concrete-encased electrode, the portion of the conductor that’s the sole connection to the concrete-encased electrode isn’t required to be larger than 4 AWG copper [250.66(B)].

In regard to the bonding portion of your question, to quickly clear a ground fault and remove dangerous voltage from metal parts, the building/structure disconnecting means must be connected to the circuit equipment grounding conductor, which must be one of the types described in 250.118. If the supply circuit equipment grounding conductor is of the wire type, it must be sized in accordance with 250.122, based on the rating of the overcurrent device [250.32(B)] (see Figure).

Caution: To prevent dangerous objectionable neutral current from flowing onto metal parts [250.6(A)], the supply circuit neutral conductor isn't permitted to be connected to the remote building/structure disconnecting means [250.142(B)].