Short circuits and fuses

The idea

Direct contact of live and neutral wires makes the current rise abruptly (short-circuiting); overloading can also come from a supply-voltage hike or too many appliances on one socket, and the fuse then melts, breaking the circuit.

A very large current

Imagine the live wire and the neutral wire of a home circuit touching each other because their insulation is damaged. There is a fuse in the circuit.

What do you expect the fuse to do?

• Melt and break the circuit
• Make the current even larger
• Do nothing at all

Too much current

Press Next step. These are pictures to read; wiring and fuses are for a trained electrician.

Fuse to the rescue

If the live and neutral wires touch, the current rises very suddenly. That is short-circuiting. Overloading can also come from a rise in the supply voltage or from too many appliances on one socket. A fuse melts by Joule heating when the current is too high, and the circuit is broken. The appliance and the circuit are saved.

Direct contact of the live and neutral wires makes the current rise abruptly (short-circuiting); overloading can also come from a supply-voltage hike or too many appliances on one socket, and the fuse then melts, breaking the circuit.

Notes

Direct contact of the live and neutral wires makes the current rise abruptly (short-circuiting); a fuse melts by Joule heating and breaks the circuit. Overloading can also come from a voltage hike or too many appliances on one socket.

Check yourself

What is it called when the live wire and the neutral wire come into direct contact and the current in the circuit abruptly increases?

Which of these can make the live and neutral wires come into direct contact?

What happens to a fuse when an unduly high current flows through it?

Which of these can cause overloading?

• Earthing. Earthing joins a metallic body to the earth wire. Short-circuiting is direct contact of the live and neutral wires.
• Parallel connection. A parallel connection is how appliances are joined across the live and neutral wires. Direct contact of those wires is short-circuiting.
• Short-circuiting — correct. Yes!
• Damaged insulation of the wires or a fault in the appliance — correct. Yes!
• A fuse in the circuit. A fuse protects the circuit. Damaged insulation or a fault in the appliance can make the wires touch.
• A switch that is turned off. A switch that is turned off stops the flow of current through an appliance. Damaged insulation or a fault in the appliance can make the wires touch.
• It carries the high current on to the appliance. The fuse stops the flow of the unduly high current by melting and breaking the circuit.
• Joule heating melts it and breaks the circuit — correct. Yes!
• It becomes the earth wire. The earth wire is a separate wire with green insulation. A fuse stops a high current by melting and breaking the circuit.
• Using an earth wire for a metallic body. The earth wire is a safety measure for appliances with a metallic body. It does not cause overloading.
• Using a fuse in the circuit. A fuse protects the circuit from overloading by melting. It does not cause it.
• Connecting too many appliances to a single socket — correct. Yes!