Temporary protective grounding of distribution circuits-revisit ten years later

The authors consider the need for temporary protective grounding, the hazards involved, wood pole testing results, and an effective method of protective grounding. Temporary protective grounding serves a definite purpose: it prevents or limits electrical shock to field personnel performing maintenance or construction on deenergized electrical circuits than can inadvertently become energized. It is noted that preventing or limiting electrical shock during an accidental energization requires a prompt interruption of the energizing source and the prevention of dangerous voltage rises at work locations. Tests demonstrated that circuit grounding to driven ground rods did indeed aid in circuit interruption but did little to limit large voltages at work locations. Further tests revealed that wood poles supporting electrical circuits were capable of conducting lethal currents at distribution voltage levels. From these studies it was concluded that grounding to ground rods alone is insufficient to prevent electrical shock to field personnel and that another method should be developed. Computerized analysis of various grounding circuits indicated that grounding to the neutral conductor of a three-phase, Y-connected system not only initiated an instantaneous circuit interruption but also limited system voltage at work locations. These results strongly indicate that grounding to the neutral system should be the foundation for protection when maintenance is being performed on deenergized distribution power circuits.<>