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How Circuit Breakers Work

Know about the working mechanism of circuit breakers from this article, and understand why they are a vital necessity for every house.
Rajib Singha
Circuit breakers
Electricity can be regarded as the next essential to food, air and water. Right from a bulb, till the washing machine, every house requires this source of energy. In case you were unaware, your house gets electricity that is delivered by a power distribution grid, which also does the same for all other houses. The electricity is delivered with the help of large wires. So the electricity flows through your house in a large circuit, which is again made up of smaller circuits. Now one end of the circuit is connected to the power grid; it is known as the hot wire, while, the other end is grounded; known as the neutral wire. Due to these two connections, a potential difference is created across the circuit, and when this circuit is closed, electricity starts flowing.
Some Basic Facts
In the United States, the standard voltage at which electricity is delivered is 120 and 240 volts. However, with different electrical appliances, the resistance differs thus, the current. As you must be familiar with Ohm's law, it stated that a current through a conductor between two points, is directly proportional to the potential difference across the two points, and inversely proportional to the resistance between them. In formula, it is I = V/R (where I = current, V = potential difference, and R = resistance). That is, the current differs when it flows between devices of different resistance.
For instance, in your house, a light bulb acts as the resistance for the current in the circuit. Now for the electricity to flow, it must work to mover further, and this work occurs in the form of heat after the filament of the bulb glows. So it is the resistance of the appliance that decides the amount of charge flowing through a circuit. That is why, every electrical appliance is designed in such a way that it operates on electricity at a safe level. Heavy current can risk the wires of not only the appliance to damage, but that of the whole building to catch a fire.
In certain circumstances, it may happen that the hot wire and the neutral wire get fused together. And this means that the hot wire is directly connected to the ground, with minimal resistance. This is known as a short-circuit, which causes a huge amount of charge to flow through the wire, risking overheating, damage to the circuit, explosion and fire. And this is where the job of a circuit breaker comes into play.
Working Mechanism of A Circuit Breaker
The work of the circuit breaker, as the name suggests, is to break the circuit and keep the electricity from flowing any further. When a short-circuit occurs, this safety appliance automatically turns itself from an 'ON' mode to 'OFF' mode. And this cuts the current from the power source to the appliance. In this way, it can prevent the appliance from getting damaged, and a fire from breaking out in the house.
This device consists of a few simple components which may include:
  • A moving, conductive contact plate
  • A stationary conducting plate
  • A switch
  • Electromagnet
  • Bimetallic strip
The contact plate is made to contact the stationary plate, which is connected to the rest of the circuit. Now a circuit breaker may use an electromagnet to work, or a bimetallic strip. In some cases, both of these are used.
If the circuit uses an electromagnet, then it works on the principle of electromagnetism. The magnitude of magnetism of the electromagnet increases with that of the electricity. And the magnet has predetermined value. Now during a power surge, when the current load exceeds this value, the magnetism becomes so powerful that it forcefully pulls down the metal lever. This in turn breaks the connection between the conductive contact plate and the stationary plate thus, breaking the circuit and ceasing the current.

Bimetallic Strip
Coming to the next section, when the appliance makes use of bimetallic strip, it is the principle of heat that is used. The strip consists of strips of two different metals which are welded together. These metals are supposed to expand as a response to heat, but at varying rates. So when a short-circuit occurs, due to the heavy current, a dangerously high amount of heat gets generated. And due to this heat, the strip bends at such a level that is enough to bring down the lever of the circuit breaker. And eventually this moves the contact plate away from the stationary plate, thus cutting the electricity.
And this is how a circuit breaker works to ensure optimal functioning of electricity in your house. But to understand the working better, practical knowledge is a must. So seek help from a professional electrician in your neighborhood, and learn more. But do not try any trick at home if you are not a professional!