Ground-Fault Protection of Equipment

DOE-HDBK-1092-98

grounding electrode conductor of the system sized by NEC Table 250-94. The four types of

electrodes are as follows:

1. Metal water pipe in contact with the earth for 10 ft. or more. Interior metal water pipe beyond

5 ft. from the water entrance shall not be used as a part of the grounding electrode system or

as a conductor to interconnect those electrodes. (See NEC Section 250-81.)

2. Metal frame of the building, where effectively grounded

3. Bare #4 conductor at least 20 ft in length and near the bottom of the concrete foundation (within

2 in.), or 1/2 in. reinforcing steel or rods at least 20 ft in length (one continuous length or spliced

together)

4. Bare #2 conductor encircling building at least 2-1/2 ft. in the ground (spliced together at each

end).

The grounding electrode conductor at the service equipment can be connected to any convenient

interbonded electrodes that provide a solid, effective connection. Metal water pipe shall be

supplemented by an additional electrode, which can be any of the following electrodes:

1. A rod

2. Pipe

3. Plate

4. Building steel

5. Concrete-encased electrode.

(See Figure 4-8, which lists some of the different types of grounding electrodes.)

4.14 GROUND-FAULT PROTECTION OF EQUIPMENT

See Section 2.7 for ground fault circuit interrupters for personnel protection. An increased degree of

protection in solidly grounded systems can be achieved in providing ground-fault protection that will

shunt trip circuit protective devices when user-selected levels of ground fault or leakage current flow

are detected in electrical circuits. This is required to be installed on all solidly grounded wye services

of more than 150 V to ground but not exceeding 600 V phase-to-phase where the service

disconnecting means is rated at 1,000 A or more (See NEC Sections 215-10, 230-95, 240-13, and

Figure 3-1).

4.15 PERSONNEL PROTECTIVE GROUNDS

Personnel working on or close to deenergized lines or conductors in electrical equipment should be

protected against shock hazard and flash burns that could occur if the circuit were inadvertently

reenergized. Properly installed equipotential protective grounds can aid in lessening such hazards by

providing additional protection to personnel while they service, repair, and work on such systems.(See

Section 7.5).

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