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I am not familiar with these topics, and my question is related to this one: Can a high voltage line kill a person without touching it?. In school I heard about step potential, which as far as I understand is essentially the potential difference between the feet of a human in an inhomogeneous electrical field (the example used lightning rod in the instant of a lightning stroke it causing a high current rushing through it). I am not sure if I explained it correctly, but if I did, then my question is: does this phenomena pose a danger around electric power lines? (By the way our teacher told us that the best we can do in such an electric field is to close our legs so our heels are touching each other.)

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  • \$\begingroup\$ The legs together thing has to do with a lightning bolt coming down in your vicinity and the voltage and current propagating across the surface of the earth. If you are standing with your legs apart in the right direction there can be enough difference in the voltage under each foot to shock you. I doubt this would be an issue with overhead power lines unless they were to discharge to ground a few feet away from you. \$\endgroup\$ – Trevor_G Apr 6 '17 at 21:41
  • \$\begingroup\$ BTW I have heard this is why birds do not sit on high voltage lines, there is a distinct difference in voltage between their feet. \$\endgroup\$ – Trevor_G Apr 6 '17 at 21:43
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    \$\begingroup\$ @Trevor I don't think that can be true. Assume the birds are annoyed by 1V across their feet, which are 5cm (2in) apart. Then the lines are dropping 1V/5cm, or 20kV/km (32kV/mi). The highest voltage used here is 380kV, so with these losses all power would be dissipated after just 19km (12mi). That clearly isn't the case. \$\endgroup\$ – marcelm Apr 6 '17 at 22:26
  • \$\begingroup\$ @marcelm the way I heard it was more to do with the 60hz wave in the transmission line, but doing some quick math those birds would have to have a heck of a crotch gap. Must be a myth. \$\endgroup\$ – Trevor_G Apr 7 '17 at 1:13
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When the insulators aren't faulty, there isn't any noteworthy current flowing from the mast into ground. So the step voltage on the ground is very low.

That is much different e.g. from an earthing circuit in a TT or SWER power distribution system. Here, there is a noteable current running into the ground and countermeasures against too high step voltages near the earthing electrode have to be taken. Usually this is done by using several ring shaped earth electrodes around the building or the mast carrying the local transformer.

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