truck6018 wrote:Ken W2KB wrote:CAR_FLOATER wrote:I am surprised that the live catenary didn't become an issue.
Highly unlikely to be an issue other than confirmation as a safety precaution that wires not energized. The traction power protection system relaying would immediately trip the breakers upon detection of the fault.
Even if the wires were not energized, does not mean they were grounded.
Just because the wires were disconnected from the high voltage source, if they were not directly connected to ground, you really don't know what the voltage on the wires is. Due to stray leakage from nearby high voltages, or residual charged capacitances, the voltage could be anywhere between the high voltage and zero (ground). If the wires were still charged to some high voltage, you couldn't pull a lot of current out of it and power anything, but the residual charge could easily be enough to hurt someone badly. That's why you ground the wire, to be sure it is at zero volts compared to ground.
It's a similar effect as in the olden days when you opened the back of your TV, etc, to change vacuum tubes to try to fix your set if it isn't working right (if you're old enough you remember taking the tubes down to the tester at the drugstore...). Even with the set unplugged, the power supply or HV capacitors could still be charged, and if you accidentally shorted them it was more than enough to scare the .... out of you, literally, at a minimum, and it could easily do far worse than that. Any TV repairman would tell you the golden rule was only one hand inside the set at a time (so you didn't accidentally put high voltage on one hand and ground on the other). JS