MAGNETIC EFFECTS OF ELECTRIC CURRENT
In homes, electric power is supplied through a main supply (mains), supported through overhead electric poles or by underground cables. In this, one wire is with red insulation cover (live wire or positive) and other wire is with black insulation (neutral wire or negative). In our country, the potential difference between the two is 220 V.
At the meter-board, these wires pass into an electricity meter through a main fuse. Through the main switch, they are connected to the line wires. These wires supply electricity to separate circuits in the house.
Often, two separate circuits are used, one of 15 A current rating for appliances with higher power ratings such as geysers, air coolers, etc. The other circuit is of 5 A current rating for bulbs, fans, etc.
The earth wire (green insulation) is usually connected to a metal plate deep in the earth near the house. This is a safety measure, especially for metallic appliances (e.g., electric press, toaster, table fan, refrigerator, etc.). The metallic body is connected to the earth wire, which provides a low-resistance conducting path for current. It ensures that any leakage of current to the metallic body of the appliance keeps its potential to that of the earth, and the user may not get a severe electric shock.
A schematic diagram of a common domestic circuits
In each separate circuit, different appliances can be connected across live and neutral wires. Each appliance has a separate switch to ON/ OFF the flow of current. In order that each appliance has equal potential difference, they are connected parallel to each other.
When the live wire and the neutral wire come into direct contact, it causes overloading. This occurs due to
o Damage of insulation of wires or fault in the appliance.
o Accidental hike in the supply voltage.
o Connection of too many appliances to a single socket.
Due to overloading, the current in the circuit abruptly increases. This is called short-circuiting. An electric fuse can prevent the damage to the circuit and appliance by stopping unduly high electric current. The Joule heating in the fuse melts it to break the electric circuit.