Magnetic Effects of Electric Current

• An electric fuse is a device which is used to limit the current in an electric circuit. The fuse safeguards the circuit and the electrical appliances from being damaged.
  
  
• The fuse wire is generally an alloy of lead and tin. It has a low melting point and breaks the circuit if the current exceeds a safe value. The thickness and length of the fuse wire depends on the maximum current allowed through the circuit.
  
  
• It is connected in series in the beginning of the electric circuits.

When the circuit current exceeds a specified value due to voltage fluctuations or short-circuiting, the fuse wire gets heated and melts. Thus it breaks the connection as shown in the figure and no current flows. This prevents damage to the appliance.

Domestic circuits may be damaged due to the following conditions:

Overloading

If too many electrical appliances of high power rating (like electric iron, water heater etc) are switched on at the same time, they draw an extremely large current from the circuit. This condition is called overloading and it can cause overheating of the wiring and lead to a fire. It can also happen due to an accidental hike in the supply voltage.

Short-circuiting

In an electric circuit a short - circuit occurs whenever the live wire and the neutral wire come in direct contact. The wires touch may each other due to faulty connection or sometimes due to the wearing off the insulation. This condition leads to overheating of the wires and causes a fire.

Earthing of Electrical Appliances

To avoid the risk of electric shocks, the metal of an electrical appliance is 'earthed'.

Earthed means to connect the metal case of the appliance to the earth (at zero potential) by means of a metal wire (copper) called the earth wire. One end of the earth wire is buried deep in the earth; the other end of the wire is connected to the three pin socket.

When the electrical appliance is switched on, the metal casing of the appliance will remain at zero potential as it is in contact with the earth wire in the three pin socket. It thus prevents us from an electric shock even if we touch it accidentally.