Encyclopedia of Grounding (CA09040E)

On a wood pole, the cluster bar is installed below the worker’s feet and the ground set connects the cluster bar to the neutral. In this case, the low resistance path in parallel with the worker is some distance away. The worker’s path consists of the length of conductor and neutral wire between the installed personal protective ground set and the worker’s remote worksite plus the jumper. In this case, it is important to know the value of available fault current and the sizeof theconductor and neutral. Using techniques described earlier, it can be determined if the division of fault current will result in a worker voltage that exceeds the maximum selected level. The direction of the cur rent source must also be considered. The circuit shown in Figure 11-4 illustrates this. A calculation is made for both the jumpers installed between the worker and the source and again for the case of the ground sets installed downstream from the worker and the source. There is a significant differ ence in the current values through the 1,000-Ohm man in these cases.

Equipotential Method on a Steel Tower Figure 11-3

Thismethodoffersprotection for theworkerwithin the equipotential zone. Otherworkers on the same tower may or may not be affected during a fault. While the tower will experience a rise in voltage, if the workers are not in a path of current flow, their bodiesmaynot bridgeadifferenceof potential. Or, a worker located between the ground set contact point and the Earth may notice an electrical shock depending upon the resistance of the steel, the amount of corrosion of the various joints, the volt age present and the resistance in the series path. In some circumstances, workingat adistance from the pole or structure with the full set of installed grounds is required. Toprovidesafetytotheworker, workingaway fromthegrounds apersonal ground set is required, consistingof acluster bar andsingle grounding jumper. Note that this method requires the installation of both the full set described as Equipotential (or single-point protection) plus the personal ground set. Worksite Remote from Grounds (Limited Distance)

I SOURCE = 10,000 Amp. R L

= 1 span conductor or 300 ft. of 2/0 ACSR = 0.024 ohm = 1 span Neutral or 300 ft. of 2/0 ACSR = 0.024 ohm = Jumper Resistance = 0.001 ohm = Jumper Resistance = 0.001 ohm = Worker Resistance = 1,000 ohm

R N

R J1 R J2 R M

L R

R M

R J1

R J2

R N

Personal Jumper, Away From Worksite Figure 11-4

CHANCE® LINEMAN GRADE TOOLS™

11-3