A short circuit takes place when current bypasses an appliance on a current path that has little or no resistance. Short circuits cause large currents to occur, producing large amounts of heat and fire hazards.
To demonstrate how a short circuit works, an iron wire, whose resistance is high, is connected to a source of power. The voltage from the power source pushes electrons through the wire against the resistance offered by the wire, and this causes it to heat up. When the wire is shortened, which reduces the resistance, and the same amount of voltage is applied, it heats up even more because of the increase in the flow of current. When the wire is shortened further, a large amount of current flows and melts the wire. This is the principle of operation of short circuits.
Fuses and circuit breakers are often used to avoid short circuits. The thin strip of wire in a fuse normally blows out when the amount of current exceeds a specific value, and this protects appliances and electrical circuits connected to a power source through the fuse. The rated current should pass through this thin strip of wire to the electrical circuits, but when the wire blows, it disconnects the circuit from the high current, which would otherwise destroy the appliances.