Re: Header pic
The idea of an earthed metal enclosure is, if a live wire comes adrift inside the appliance and then touches the metal case, the fuse will blow.
If you insert a Schuko (earth connection by means of contacts at the edge of the plug) or French / Czech (earth connection by means of a pin protruding from the socket) plug into a non-earthed socket, the metal case of the appliance will not be earthed. Now if a live wire comes adrift inside the appliance and touches the metal case, it will become live.
An RCD measures the difference between current flowing out the line and returning up the neutral -- which should be equal. If they are different, either Kirchoff was mistaken (which is actually not impossible, since verifying either of Kirchoff's Laws or Ohm's Law requires the use of test instruments which rely for their operation on those laws being true in the first place) or some electrons have unilaterally decided to take a different route back to the supply, possibly via you. So the RCD disconnects the supply.
Either a fuse or an RCD will offer protection against a live wire touching an earthed metal housing. (Other faults are available.)
Biting the hand that feeds IT
