Science Projects Index

The Main Circuit Breaker

The Main Circuit Breaker (MCB) is a device that maintains the safety of the electrical gadgets. Often, there is a fluctuation in the supply of electricity. The voltage may suddenly increase and may damage the electrical gadgets. Sometimes, it may also cause short circuit and fire. The main circuit breaker or MCB prevents this.

Let us see how an MCB works.

Things Required : A thick cardboard eight inches by 10 inches, two feet of wire, 4 clips, pliers, 9 volts magnetized wire with a plunger, 220 ohms resistor, battery connector, adhesive tape, aluminium foil, wire strippers, scissors, 9 volts battery, six 2.5 cm polyboard square, some empty match box and a LED

Method : The pins of the LED and resistor are inserted in a small cardboard square so that the anode of the LED is next to a resistor pin. The two pins are twisted together. The free pins are bent so as to project them beyond the square. A right angle bend of the paper clip is made. The horizontal portion of the bend is taped to the positive pole of the battery. The LED square is fixed on the empty matchbox already fixed vertically. The free end of the LED leg is connected to the negative terminal of the battery. Then the magnetized wire is placed on an empty matchbox. The plunger should touch the clip contact when it is half way out of the coil. One of the magnetized wires is connected to the resister leg which is projecting out from below the square. A small aluminium foil is connected to the other wire. The end of the plunger is taped to the foil. If the magnetized wire is pulled, it touches the paper clip, the LED lights up.

Connecting the resistor legs and the uncovered LED creates a short circuit. A wire is used to connect these. The electric circuit, which was supposed to have gone to the LED by passes it. As a result a high current enters the wire. It increases the coil's magnetic fields and pulls the plunger in to break the circuit.