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GROUNDED SYSTEMS – SUPPLIED BY A FEEDER OR BRANCH CIRCUIT
250.32(B)(1)
Where a building or structure is supplied from a service in another building by more than one branch circuit, a -grounding electrode shall be installed at the additional building(s) or structure(s) being served. The equipment grounding conductor run to the other building or structure shall be sized per Table 250.122.
Where livestock is housed, the equipment grounding conductor shall be insulated or covered where routed with the feeder or branch circuit and bonded to the metal case of the enclosure.
Note, the neutral bus and grounded (neutral) conductor is isolated from the case. See 250.142(B) and 408.40 for rules pertaining to this type of installation. (See Figure 16-55)
Design Tip: An individual equipment grounding conductor shall be installed to provide an effective return path for the fault current to travel over instead of using a grounded (neutral) conductor for such use. This particular installation is used to prevent the grounded (neutral) conductor and equipment grounding conductor from joining together at both ends, which if done, provides a parallel path for stray currents to travel over; this is not desirable for such an installation and causes problems for certain types of equipment.
For example: A 150 amp (75°C terminals) panelboard in building 1 is supplied by 3 - 1/0 AWG THWN copper conductors and the neutral calculated load is 48 amps. The feeder is protected by a 150 amp overcurrent protection device (75°C terminals). What size grounded (neutral) conductor and equipment grounding conductor is required using THWN copper conductors in the feeder?
Step 1: Finding grounded (neutral) conductor in feeder
215.2(A)(1), Ex.'s and Table 310.16
48 A load requires 8 AWG cu.
Step 2: Finding EGC in feeder
250.122(A) and Table 250.122
150 A OCPD requires 6 AWG cu.
Solution: The size of the grounded (neutral) conductor is 8 AWG copper and the equipment grounding conductor is 6 AWG copper.
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