How Does a Fuse Box Work?

Written by laura reynolds
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How Does a Fuse Box Work?
(Heimer Engineering, Microsoft Office clip art)

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A fuse box is a type of electrical panel that provides both a routing and a safety mechanism for electricity as it enters your home. When the utility company brings electrical service into your home through a set of overhead wires or (more likely in new homes) an underground cable with a junction box, the electrical panel splits the power into circuits that connect the electricity to its destinations within the house. Circuits are routed out the opposite side of the panel through open positions where fuses are inserted to complete each circuit. Large appliances like the furnace and air conditioner are often attached to single or "dedicated" circuits.

Traditional plug" type fuse used for household circuits
Traditional plug" type fuse used for household circuits

Each circuit has a safety device--a fuse or circuit breaker--that controls how much current can travel through it. A fuse contains a filament that burns out, breaking the circuit, when the maximum load that the circuit can carry has been reached. A fuse may blow due to any number of reasons including a short circuit in an appliance, a problem in the wiring or a power surge in the electrical supply. Before replacing a fuse, it's wise to track down the problem. If the cause is overloading of the circuit, some appliances must be moved to another circuit. Almost all electrical panels will have one or more "main" fuses or breaker switches. A main fuse is generally a cartridge with blade-shaped ends that is placed between the supply line and the circuits. When a main blows, it's time to call an electrician to see if there's a problem with the service or if it's time to upgrade either the service or electrical panel.

An automotive fuse with blade end
An automotive fuse with blade end

Fuse boxes, being an older technology, tend to require more maintenance and may intimidate a new homeowner. Provided you've had a licensed electrician give your wiring and electrical circuitry a clean bill of health, the only difference between a fuse box and a circuit breaker panel is that, when a fuse blows, you have to unscrew the old fuse and replace it with a new fuse rated for the same amperage as the old one. Putting a fuse with higher amperage in is dangerous because the wiring in the circuit may not be able to carry the greater load safely, leading to a fire hazard. If you find yourself replacing fuses often and your wiring is sound, an electrician will probably advise you to change your service to a higher supply. When electricity was first supplied to households in the early 20th century, most used 90 "amp" service for a few lamps and a radio. Today's homes, with their air conditioners, high resistance appliances like dishwashers and numerous electronics, require 200 to 300 amp service. Upgrading service requires more than just changing a fuse panel. It also means that new circuits will need to be added and old ones rewired to keep the house safe. Community building codes have increasingly mandated replacement of fuse boxes with circuit breaker panels when supply service is upgraded.

How Does a Fuse Box Work?
A fuse used in electronics

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