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Article 250 Low Res - Modem [1695Kb] Hi Res - Cable/DSL [5622Kb]        Page 4 of 5

Circuit and System Grounding

250.32 Buildings or Structures Supplied with Feeder

This subsection added a new requirement and it reads:

(B) Grounded Systems.
(2) Grounded (neutral) Conductor.
Where (1) an equipment grounding conductor is not run with the supply to the building or structure, and (2) there are no continuous metallic paths bonded to the grounding system in both buildings or structures involved, and (3) ground-fault protection of equipment has not been installed on the common ac service, the grounded circuit conductor run with the supply to the building or structure shall be connected to the building or structure disconnecting means and to the grounding electrode(s) and shall be used for grounding or bonding of equipment, structures, or frames required to be grounded or bonded.

The size of the grounded conductor shall not be smaller than the larger of:
(1) That required by 220.22 (maximum unbalanced neutral load), or
(2) That required by 250.122 (equipment grounding conductor size).
Figure 250–10

Intent: The changes to this section should make it much easier to understand the grounding and bonding requirements contained in Article 250. The most significant change includes the explanation that, in order to clear a fault, the fault current must have an effective low-impedance ground-fault current path back to the grounded (neutral) terminal at the power supply.

Author’s Comment: When an equipment grounding conductor is not run to a separate building or structure, the grounded (neutral) conductor must be used to provide the effective fault current path required to clear any line-to-case faults in addition to carrying any unbalanced neutral current.

Figure 250–10
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