Electrical safety touch potentials

Safety Bond a bond connecting the metallic carcase of a piece of electrical apparatus with earth, in order to limit the rise in potential of the carcase above earth caused by the passage of any fault current or excessive leakage current, and so reduce the risk of electric shock to anyone touching the carcase. 

An electrical plug has three connections (or pins ) live , neutral and earth . The earth pin is necessary for safety considerations. The potential of the earth pin is the same as that of the ground, so there is no potential difference if we stand on the ground and accidentally touch the earth pin in a plug or electrical appliance. We will not be electrocuted. Conversely, the potentials of the other pins are different from that of the earth - in fact, we sometimes cite their potentials with respect to the earth pin, effectively delining the potential of the ground as being zero. 

For third party safety the concern is mainly coming from the potential accidental touching of live electrical system parts, e.g. the conductor wires of overhead lines. 

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