How to calculate fuse size

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A fuse is put into an electrical circuit to protect it from overloads. In a piece of electronic equipment, it can prevent damage to critical components by shutting off an overload. In a home, it is designed to prevent fires by shutting the power off in the event of short circuits or high voltage. Using a properly sized fuse is important in both situations. An undersized fuse will prevent adequate current reaching its destination. An oversized fuse can defeat its original purpose by allowing too much current to flow through a circuit.

Calculating a fuse size

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Determine the operating voltage of the power source.

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Determine the watts required by the circuit.

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Use a calculator to divide the number of watts by the voltage. In the case of a 110-volt circuit, using 1200 watts, the calculation would be: 1200/110=10.9 amps. For a household circuit, a 15-amp fuse should be used in this circuit. A 10-amp fuse would "blow-out" consistently before the necessary power was delivered. A 20-amp fuse could overload wiring designed for a load of 1200 watts on a 110-volt circuit.

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