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Every electrical device in your home that is connected to a power supply is protected by a fuse somewhere along the circuit connecting it to electrical supply. Your riding lawnmower has fuses to manage electrical power for the machinery controlling the blades and attachments. Your video games, television and computer have built-in fuses to protect delicate circuits. The biggest fuses in your house are located in the fuse or circuit breaker panel that's mounted on the wall where electrical power lines come inside your house and split into the circuits going to every room and large appliance. Without fuses, power surges from electric generators or short circuits within your house could burn out appliances, circuit boards and wiring. Any of these could lead to fires or further damage to the electrical systems within the building. New and complex methods of managing electrical current have been developed in the last fifty years, but fuses are the oldest and simplest way to safeguard your home or business.
All fuses are part of the circuit they protect. They all contain a filament or strip made of metals with different melting points that complete the circuit, connecting prongs, blades or a metal jacket and knob. This filament melts and breaks when a certain amperage or "load" has been exceeded. A new fuse must be used to re-establish the circuit. Most household circuits carry 10, 15 or 20-ampere loads. An ampere is a unit of electric current or movement of coulomb per second of electricity. Every appliance has a tag on it that tells not only how many watts of energy it produces but also how many amperes it requires to produce it. Watts are computed by multiplying the number of amps times the volts, or electric current. A table lamp with a 60-watt bulb would only use three-tenths of an amp, assuming that the power supply is the standard North American 220 volts. Heavy appliances like furnaces, air conditioners, dryers and dishwashers that have higher load requirements are usually connected to dedicated circuits---circuits wired only for that appliance---to guard these expensive and important pieces of equipment. No matter what the load, the filament will melt and the fuse will "blow" when the amperage is exceeded.
A blown fuse can signal a problem in a circuit, or it may simply be a warning that a circuit is carrying a load from too many appliances or that lightning or a generator has caused a power surge. Fuses come in a variety of types and should always match the amperage of the circuit that they protect. Fuses may be "fast-acting" or "slow-blow." Delicate electronic equipment should always be protected with the fast-acting fuse that blows before a power surge, or the short can cause more damage. Slow-blow, or delay, fuses are often used in basic household circuits to avoid repeated fuse replacement on circuits that are connected to lights and other devices that are turned on and off frequently.