12.4.1. Wiring and Components

In our homes, we receive supply of electric power through a main supply (also called mains), either supported through overhead electric poles or by underground cables. One of the wires in this supply, usually with red insulation cover, is called live wire (or positive). Another wire, with black insulation, is called neutral wire (or negative). In our country, the potential difference between the two is 220 V.

Electric power is supplied to our homes through either overhead poles or underground cables. The wires that bring this power have different functions and colors: the live wire, which is typically red, carries the electrical current to our devices, while the neutral wire, usually black, completes the circuit by bringing the current back. The voltage difference between these two wires is normally 220 V, which is the standard in many countries.

Think of the live wire as a water pipe delivering water to a garden, while the neutral wire is like a drainage system that allows the excess water to flow back. If one wire (like the water) is blocked, the circuit doesn't work, just as plants don't get watered if the drainage isn't clear.

At the meter-board in the house, these wires pass into an electricity meter through a main fuse. Through the main switch they are connected to the line wires in the house. These wires supply electricity to separate circuits within 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 main wires lead into a meter-board, where the electricity meter records how much electricity is being used. A fuse acts as a safety device to prevent overload. The main switch controls the connection to various circuits throughout the home. High-power devices like geysers and air coolers use a 15 A circuit, while lower-power devices like lights and fans use a 5 A circuit.

Consider the meter-board as a traffic control center. Just as a center directs traffic to prevent accidents, the fuse and switches help manage electricity flow to avoid overloads that could cause damage.

The earth wire, which has insulation of green colour, is usually connected to a metal plate deep in the earth near the house. This is used as a safety measure, especially for those appliances that have a metallic body, for example, electric press, toaster, table fan, refrigerator, etc. The metallic body is connected to the earth wire, which provides a low-resistance conducting path for the current. Thus, 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.

The earth wire, identified by its green insulation, is a critical safety feature. It connects electrical appliances to the ground, helping to prevent electric shocks. If there is a fault and electricity leaks to the appliance's metal body, the earth wire directs that electrical current safely into the ground, thus protecting anyone who touches the device.

Think of the earth wire as a safety net for a circus performer. Just like a net catches a performer if they fall, the earth wire catches any electrical flow to the ground, ensuring no shock for the person using the appliance.

Electric fuse is an important component of all domestic circuits. We have already studied the principle and working of a fuse in the previous chapter. A fuse in a circuit prevents damage to the appliances and the circuit due to overloading. Overloading can occur when the live wire and the neutral wire come into direct contact. This occurs when the insulation of wires is damaged or there is a fault in the appliance. In such a situation, the current in the circuit abruptly increases. This is called short-circuiting.

Fuses are crucial for protecting household circuits. If too much current passes through a wire, it can cause damage. A fuse melts when there’s an overload, breaking the circuit before it can cause harm. Overloading, like when a live wire touches a neutral wire, can lead to a dangerous short-circuit.

Imagine a fuse as a safety cap on a soda bottle. If too much pressure builds up, instead of the bottle exploding, the cap pops off, releasing the pressure. The fuse does something similar by breaking the circuit to prevent damage.

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