Grounding Requirements

DOE-HDBK-1092-2004

indicators or alarms, or both, and qualified personnel are available to quickly locate and eliminate

such ground faults. Ground faults must be promptly removed or the service reliability will be

reduced. See NEC for requirements on installing a high-impedance grounding system. (See

Figure 4-4.)

NEC 250.36

Figure 4-4. A high-impedance grounding system has a high-impedance unit, installed

between the grounded (neutral) conductor and the grounding electrode conductor,

which is used to regulate fault current.

4.6

GROUNDING REQUIREMENTS

Alternating current systems of less than 50 volts shall be grounded as required in NEC.

Systems of 50 to 1,000 V should be solidly grounded as required by NEC. Systems supplying

phase-to-neutral loads shall also be solidly grounded (See Figure 4-5). The following electrical

systems are required to be solidly grounded:

240/120-V, single-phase, three-wire

208Y/120-V, three-phase, four-wire

480Y/277-V, three-phase, four-wire

2 4 0 / 1 2 0 - V , three-phase, four-wire, delta (midpoint of one phase used as a

grounded circuit conductor)

The following systems are not required to be solidly grounded:

4-6