My apologies, Trumpy. I completely overlooked your post from last week.
Paul explained it very well.
As I understand it, 'touch' (hand-to-foot) and 'step' (foot-to-foot) voltage comes about during a medium or high-voltage fault where earth return and ground currents are involved. Ohm's law applies here. When the situation is modeled or described, [too often after an accident] the path is depicted as a number of series/parallel resistors.
So, for instance, for an 11kV circuit {11kV/sqrt3 or about 6.4kV to ground} where the downed line touches soil, with return current back to the substation ground mat [usually solidly connected to the serving {~66-11kV} transformer's secondary-neutral terminal.] The across-the-earth voltage at the point of soil contact forms 'gradient rings,' where the voltage from one foot to the other can be of deadly proportions. Unless specially constructed and so rated, shoe soles are effectively very poor insulators. It can be a staggering, confusing, almost unbelievable experience.
Note that for low voltage, 'earth return' current should not be expected to reliably clear overcurrent devices, where in medium-voltage [>2kV] faults it is intended to be sensed by and operate overcurrent-protective devices.
Conductor movement from an unsecured (fallen) span contacting the earth is subject to wild gyrations from arcing and magnetic forces. It can look very much like the exaggerated scenes you find in a Disney television cartoon.
Vitrification can occur, where sand turns into glass from very high heat.
![[Linked Image from 64.146.180.232]](http://64.146.180.232/imag/jlc.fborges.jpg)
Remembering that the safest thing to do is "never turn the switch on in the first place," utility and industrial electrical engineers spend significant resources in trying to best decide what makes a reasonably safe system when someone finally does "turn the switch on." A modern term for this process is
risk management, but for electricity it's been extensively practiced for well beyond the last century.
[This message has been edited by Bjarney (edited 06-28-2003).]
