Domestic electric circuit explanation

The electricity generated from the power station is distributed to domestic and industrial users by overhead and underground cables. The first stage of the domestic circuit is to get the power supply to the main box from a distribution panel like a transformer.

The main components of the main box are the Fuse Box and Meter. The meter records the usage of electrical energy. The fuse box contains either fuse wire or MCB(Miniature Circuit Breaker)
The prime application of MCB or Fuse Wire is to protect the electrical appliances in the home from overloading due to excess current.

Mcb diagram: Mcb which is used for saving electrical devices in the time high voltage, electrical leakage etc
mcb diagram

An MCB is a switching device that can be activated automatically and manually. The MCB has a spring attached to the switch which is attracted by an electromagnet when an excess current passes through the circuit.

Thereby the circuit is broken and the protection of the appliance is ensured. The electricity is brought to the house by two insulated wires. One wire has red insulation called the live wire.
The other wire has black insulation called the neutral wire.

The alternating current of the electric potential of 220 V is supplied for domestic purposes. Both the live and neutral wires enter the box where the main fuse is connected with the live wire.

After the electricity meter, these wires enter into the main switch, which is used to discontinue the electricity supply whenever required.

After the main switch, these wires are connected to live wires of two separate circuits.
Out of these circuits, one circuit is of a 5A rating, which is used to run the electric appliances with a lower power rating, such as tube lights, bulbs, and fans.

The other one is a 15A rating, which is used to run electric appliances with a high power rating, such as air conditioners, refrigerators, electric iron, and heaters.

All the circuit is home is connected in parallel so that the disconnection of one circuit does not affect the other circuit.

Also, the parallel connection of circuits is that each electric appliance gets equal voltage.
In India domestic circuits are supplied with an alternating current of potential 220/230V and frequency 50Hz.

In countries like the USA and UK, an alternating current of potential 110/120V and frequency 60Hz is supplied.

Overloading and Short-Circuiting

The fuse wire or MCB will cut the circuit if there occurs overloading and short-circuiting. Overloading occurs when a large number of devices are connected in series to the same source of electric power.

This points to a flow of excess current in the electric circuit. If the quantity of current passing over a wire surpasses the highest allowable limit, the wires are heated to such a level that may cause a fire. This is called overloading.

When a live wire gets in touch with a neutral wire, it creates a short circuit. This occurs when the insulation or the packing of the wire gets degraded due to temperature variations and some other outside forces.

Due to the short circuit, the effective resistance in the circuit becomes very small, which starts the flow of a high current via the wires. This results in the heating of wires to such a level that a fire may be caused in the building.


A third wire called earth wire has a green covering or insulation connected to the body of the metallic electric appliance. Another end of the earth wire is connected to a metal tube or a metal electrode, which is buried into the ground.

This wire provides a low resistance path to the electric current. The earth wire conducts the current from the body of the electric device to the Earth, whenever a live wire unexpectedly touches the body of the metallic electric device.

Thus, the earth wire helps as a shielding conductor, which protects from electricity.

Consumption of electrical energy

Usage of Consumption of electricity is based on two factors: Amount of electric power duration of usage example 100 watt of electric power is used for 2 hours, then the power consumed is 100 x 2 = 200-watt hour.

Consumption of electrical energy is measured in Watt Hour, though its SI unit is watt-second.In practical terms, a larger unit is called kilowatt-hour (kWh). One kilowatt-hour is also called one unit of electrical energy.

One kilowatt-hour means an electrical power of 1000 watt used for one hour.Thereby, 1kWh = 1000 watt hour = 1000 x (60×60) watt second = 3.6 x 106 J.

* * All the Notes in this blog, are referred from Tamil Nadu State Board Books and Samacheer Kalvi Books. Kindly check with the original Tamil Nadu state board books and Ncert Books.