Criteria for Personnel Protective Grounds

DOE-HDBK-1092-2004

Figure 4-9. Equipotential personnel protective grounds are used to protect electrical

workers while they service, repair, or are close to circuits that can be accidentally

reenergized.

4.15.2 CRITERIA FOR PERSONNEL PROTECTIVE GROUNDS

Before personnel protective grounds are selected, the following criteria shall be met for their

use, size, and application.

1. A grounding cable shall have a minimum conductance equal to #2 American Wire Gage

(AWG) copper.

2. Grounding cables shall be sized large enough to carry fault current long enough for the

protective devices to sense and the circuit breaker to clear the fault without damage to

cable insulation. An example would be a 4/0 Neoprene-insulated welding cable that will

pass 30,000 A for 0.5 sec without melting its insulation.

3. The following are factors that contribute to adequate capacity:

a. Terminal strength depends on the ferrules installed on the cable ends

b. Cross-sectional area to carry maximum current without melting

c. Low resistance to keep voltage drop across the areas in which personnel are

working at a safe level during any period to prevent reenergization. The voltage drop

should not exceed 100 volts for 15-cycle clearing times or 75 volts for 30-cycle

clearing times.

d. Verify that the grounding cable and clamp assembly is tested periodically by using

the millivolt drop, micro-ohm meter, AC resistance, or DC resistance test methods.

For example, if it is desired to maintain a maximum of 100 volts across a worker

whose body resistance is 1000 ohms, during a fault of 1000 amperes, a personnel

protective ground resistance of 10 milliohms or less is required.

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