INSULATION : There are two types of insulation, double insulation is when there is an earth wire AND a plastic casing. this is double iion as the earth wire prevents an electric shock and plastic is an insulator. when the casing of the plug is metal an earth wire is required to prevent harm in the event the live wire becomes frayed. EARTH WIRE : an earth wire is present so if the live wire becomes damaged and comes into contact with the outer casing of the plug (if it is metal) it allows the current to flow into the earth wire thus preventing an electric shock if someone were to touch the plug. THE FUSE/ CIRCUIT BREAKERS: a fuse is made from a metal with a low melting point, it is connected to the live wire and when too large a current flows it melts the fuse and shuts off the circuit, preventing damage. Circuit breakers serve the same purpose as fuses but they act diferently. if too large a current flows a switch in the circuit opens, breaking the circuit and stopping electrical flow.