The Practice and Effectiveness of Equipotential Zone “EPZ” Grounding-Safety Reality or Pipe Dream?

Abstract

Since 1994, Occupational Safety and Health Administration (OSHA) regulations of 29CFR1910.269 subpart R and 1926.962 subpart V [1], has required temporary protective grounding to be placed in such locations and arraigned in such a manner that will prevent each employee from being exposed to hazardous differences in electric potential. This practice is commonly called Equipotential Zone or “EPZ” grounding and bonding or “single-point grounding”. However, some debate exists as to the effectiveness of EPZ grounding with some employers still preferring to use bracket grounding practices, i.e. “Bracketed by Grounds” which is often referred to as “Working Between Grounds”. This paper will attempt to demonstrate the effectiveness of EPZ grounding when it's properly established though a significant real-life electrical event where two workers were uninjured when the metallic equipment, they were in contact with had become unexpectedly energized at approximately 303 kVac during the preparation of live line bare-hand work (LLBHW). Applicable lessons learned related to the properly sizing temporary ground cables, using materials and parts specifically designed and rated to withstand the tremendous X/R mechanical forces imposed during a fault will also be presented.