Figure 4-4. A high-impedance grounding system has a high-impedance unit, installed between the grounded (neutral) conductor and the grounding electrode conductor

DOE-HDBK-1092-98

NEC Section 250-27

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 Section 250-

5(a). Systems of 50 to 1,000 V should be solidly grounded as required by NEC Section 250-5.

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:

1. 120/240-V, single-phase, three-wire

2. 208Y/120-V, three-phase, four-wire,

3. 480Y/277-V, three-phase, four-wire,

4-7