A crew tests a line dead, locks it out, and starts work. A mile away, someone makes a switching error and backfeeds the line through a tie. One worker is standing on the ground with a hand on the conductor. Before you read on, predict it: with protective grounds installed, what does that worker feel? And without them?
The honest answer to the second case is that without grounds and an equipotential zone, the conductor can jump to full voltage and that worker becomes the path to earth. A line that tested de-energized can be re-energized by a switching error or backfeed, by induction from a parallel energized circuit, or by lightning. Tested-dead tells you the state at the moment you tested. It says nothing about the next minute.
That is why protective grounds go on every time, even after a clean test and lockout. A de-energized line is not a dead line. The grounds do two jobs at once: they give any returning fault current a low-impedance path back to the source, and they bond the work zone into an equipotential zone.
The equipotential zone is the part that keeps the worker breathing. Current flows through the body only when there is a voltage difference across it. So you bond everything the worker contacts, the conductor, the jumpers, and the standing surface, to the same potential. If the line snaps back to voltage, the conductor and the worker rise together, almost no difference appears across the body, and the current bypasses it through the bonded jumpers instead. The zone does not work by draining the line to earth alone, because earth is not a perfect sink.
The two hazards the zone defeats have names worth knowing. Step potential is the voltage between your two feet across the soil’s voltage gradient during a fault. Touch potential is the difference from a hand on equipment to your feet. Bond the worker into one potential and both differences collapse toward zero. This is educational framing, not a protection study, but the rule on the pole is simple: ground it, bond it, and treat every de-energized conductor as if it could come alive.
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