Till the poles near houses, electricity reaches through the distribution system. Two wires from the poles come to the houses. Among these, one wire is called as phase while the other is called as neutral.
In the phase wire the voltage is 220 V while in the neutral the voltage is zero same as that of earth. It is represented as N. Usually the phase wire has a red coloured insulation over it while neutral wire has insulation of any colour other than red or green. Inside the houses wiring is done in parallel mode such that when one lights an appliance in a room it doesn't affect the strength of current in another room.
We use another wire that has green coloured insulation over it which is called as earth wire or earth-connecting wire. All the appliances are connected to this to the earth.
Several dangerous accidents have occurred due to electricity at homes or industries. Such accidents by electricity occur due to the following reasons:
1. Leakage of Current
Often due to continuous flow of electric current the insulation over wires gets affected and is scraped off and the wires are left bare. Current leakage occur through such bare wires. Often these bare wires in contact with a metallic surface increase its voltage to that of the main source. The surface of the metal if comes in contact with earth, allows current flow into the earth. When a person touches such appliances gets a severe shock.
2. Short Circuit
If somehow the main and neutral wire come in contact with each other there is a sudden huge spark that takes the form of fire.
If several appliances are connected to the same circuit there is an overload in the circuit. The value of current flow goes above the required value of the circuit. At this juncture the wire fails to bear the load of electric current. This is called overloading. Household appliances are connected parallel to each other in the circuit. The greater the amount of resistance the source would take more of current. During summer when the demand on electricity increases, transformers often burn due to extra load.
1. Electrical Fuse
A piece of wire made of lead and tin alloy is used in making fuse. It has its melting point lower and high resistance then that of electrical wire. Due to this, if current in a circuit increase above a particular point the fuse wire gets heated and burns out. Due to this the whole circuit is saved from burning. The fuse wire is connected to the main source in series. Usually 5 A (ampere) fuse is used for household appliances, while 15 A fuse is use for power circuits. 15 A fuse wires are thicker than 5 A fuse wires.
2. Miniature Circuit Breaker (MCB)
These days MCB is attached to the household circuit wirings. MCB is a self regulatory switch which saves the circuit from overloading as well as from short circuits. If there is any barrier in the flow of electrical current it immediately stops the flow of current. Fuse is also used for this purpose but MCB is prepared in different shapes varying in use from small to large appliances saving them from high voltage.
3. Earthing of Electrical Appliances
Leakage of electric current in electrical appliances can harm us and may get electrical shock by touching them. Thus, as a precaution there is another wire other than phase and neutral which is called as earth wire. The metallic end of all appliances is connected to one end of this wire and the other end is attached to a copper plate and buried deep in the ground.
Thus, the body of all electrical appliances is of the same potential difference as that of the earth. If ever we come in contact with electrical current, the path of earthing would be shorter than that through our bodies and thus we would be saved as current would flow through the alternative (earth) pathway rather than through our bodies.