Gary Zevenbergen, Electrical Engineer – Western Area Power Administration
Linemen, working on de-energized high-voltage transmission lines, can be exposed to electric shock hazards. Proper use of clearance procedures, as outlined in OSHA 1910.269(m), and a properly installed work site grounding system are utilized to mitigate these shock hazards. However, not all shock hazards can be removed from the work site. Shock hazards associated with ground potential rise, namely step voltage, will exist anytime current is injected into the earth through the work site grounding system. The severity of these shock hazards has been documented numerous times through stage fault tests by energizing a transmission line with a work site grounding system installed and recording the resulting exposure voltages at the work site.
Although the most severe ground potential rise shock hazards are generated by accidentally energizing the grounded transmission line, however, lethal shock levels can be created by currents induced into the work site grounding system from parallel energized transmission lines. These induced shock hazards, however, are not always present.
This seminar will examine three shock incidents caused by induced currents and discuss the importance of providing real-time monitoring of the work site ground potential rise which can alert linemen to the presence of shock hazards at the work site.