An electric heater with a metal casing is connected to the 230 V, 50 Hz UK mains supply. The potential variations of the three wires in the three-core supply cable (live, neutral, and earth) under normal, fault-free operating conditions are shown below.
Which of the following statements correctly describes the currents in, and safety functions of, these wires?
The live and neutral wires carry equal alternating currents, while the earth wire carries no current under normal conditions. If a fault occurs and the live wire touches the metal casing, a large current flows to the ground through the earth wire, melting the fuse in the live wire.
The live wire carries alternating current with a peak potential of 230 V230\text{ V}230 V, and the neutral wire carries no current because it is held at 0 V0\text{ V}0 V. The earth wire carries a small continuous safety current to ground.
The live and earth wires carry equal alternating currents to complete the circuit, while the neutral wire only carries current when the heater is switched off. If a fault occurs, the fuse in the neutral wire melts to isolate the appliance.
The live and neutral wires carry equal alternating currents, while the earth wire carries excess oscillating charge under normal conditions. The fuse is located in the earth wire to disconnect the ground path during an electrical surge.