Prior to 2009, ASTM F855, Standard Specifications for Temporary Protective Grounds to Be Used on De-energized Electric Power Lines and Equipment only included one table indicating the specifics to which ground set designs were to be tested. This “Table 1” was based on a near symmetrical current, limiting the circuit inductive reactance to resistance (X/R) ratio to a maximum of approximately 1.8 (20% asymmetry).
In the event of a fault current, milliohms can make the difference between a lineman going home for the day or being seriously injured or killed. With fault currents in the tens of thousands of amps or more, the parallel path to the lineman needs a resistance so low that milliohms do make a difference.
When overhead electrical line workers employ proper personal protective grounding practices they are usually protected from electrical hazards that might arise from working on de-energized lines and equipment. But, what about workers at ground level? How are they protected, and from what kinds of situations are they protecting? The answer is from hazardous differences in step and touch potentials.
Recent updates to OSHA 1910.269(n) and 1926.962 have emphasized the responsibility of the employer to ensure their personal protective grounding equipment and practices are adequate to protect employees from hazardous differences in electrical potential. One important aspect that is often overlooked is the care and maintenance of the grounding equipment.
“We have been searching for better ways to implement our policy for substation grounding almost since we adopted it. While the grounding equipment we’ve been using is the widely-accepted standard for this application, it has always had room for improvement in practice,” shared a utility.