gfci for human protection, H-N and H-H shorts?

Question

I quote this from the wikipedia((Residual current devices)) ((It cannot protect against electric shock where current flows through a person from phase to neutral or phase to phase, for example where a finger touches both live and neutral contacts in a light fitting. It is virtually impossible to provide electrical protection against such shocks as there is no way for a device to differentiate between current flow causing an electrical shock to a person and normal current flow through an appliance)) is it really impossible or our existing knowledge falls short of such acheivment?.

Answer 1

Think about it. An electron flows out of the GFCI, through the body (through the heart) and back into the GFCI device. The GFCI device sees one electron leave, and one electron return. All is normal (as equal numbers of electrons are leaving and returning to the GFCI).

How is those electrons that pass through the body as a shock any different than electrons that pass through a light bulb to excite some tungsten atoms?

If you could figure out some way to ask those electrons where they have been, I suppose you could make a 'smart' GFCI. I don't know any way to ask electrons where they have been. Even if you could find out where the electrons have been, you have another problem. Individual electrons do not travel at the speed of light, they travel at a drift velocity, which is much slower than the speed of light, so it may take more time than a person being electrocuted has, to query the electrons returning to the 'smart' GFCI.

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Answer 2

A GFCI device protects a user by comparing the amount of current leaving the device to the amount returning, and if the amounts aren't the same, the device interupts the flow of electricity. The theory is if the amount returning isn't the same as the amount leaving, there's a "short circuit" to ground via another (unintentional) path, presumably through a person, so to prevent electrocution, the GFCI device interupts the current flow. Based on this design, a person can still be electrocuted by a GFCI outlet if all of the current passing through him/her returns to the outlet without returning to earth ground via another path.