>> Nope. As the Wikipedia article explains, there are sprung-loaded plastic
>> covers that only move out of the way as the earth pin is inserted.
>
>  Is it guaranteed that the difference in potential between the earth pin
> and the physical ground is always very close to zero?

The Earth wires in your house (in the UK at least) are connected to the 
physical ground at your house, usually by being connected to the mains water 
pipe or some similar big lump of metal in the ground.  So I don't think 
there can be much of a difference, there is probably some building standard 
that gives limits on the resistance.  I assume these limits are set so that 
any potentially dangerous Earth voltage would result in the current in the 
defective device blowing a fuse.

Post a reply to this message