A watt is an unit of electrical power and is used to measure the amount of power an appliance needs and consumes when working. A light bulb could be as low as 40 watts, where a washing machine could be as much as 3000 watts. On the casing of appliances there is a plate which states the required voltage and the wattage of that particular unit as well as other information. Because wattage is a measure of electrical consumption, the cost of electricity is calculated by it.
Voltage, watts and amps are directly related and it's important to understand how they work together as having their respective values enables calculations to be made in respect of electrical safety, running costs and consumption. For example, by having the amps and volts measurement, the wattage requirement of the appliance can be calculated, where by having the wattage and voltage can provide the amps rating. If the required rating of a fuse, or size of cable to attach to an appliance such as a washing machine at 2000 watts (2kw) is in doubt, by dividing the wattage (as shown on the appliance) by the voltage, gives us the amp rating for that particular appliance. In this case, 2000 divided by 230, equals 8.7 amps, and the correct rating of the fuse should be the nearest size above the required amperage of the appliance or circuit that it is protecting. By using the formula described here to calculate the amps the correct fuse can be chosen. In this case, a 13 amp fuse.
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