Figure 1: A fuse box in a basement[1]

A fuse is an electrical safety device that has the capability to protect an electric circuit from excessive electric current. Fuses are destroyed during overload conditions, whereas circuit breakers are often used instead because they are not destroyed during overload conditions. It's cheaper to install fuses than circuit breakers, but since fuses need to be replaced and circuit breakers don't, fuses have a higher operational cost.

Practical tips

Houses have fuses in fuseboxes (see figure 1). Here are some helpful household tips for homes with a fuse box.

  • Never replace a fuse with a larger fuse, as this will let too much current through and be a fire hazard.
  • Replacing a fuse with a smaller-sized fuse is also a problem because this will prevent normal operation.
  • Never use something other than a fuse to replace a fuse; this will quite likely cause a fire.
  • Keep extra fuses around the house to quickly replace blown fuses.
  • Know where your fuse box (see figure 1) is.
  • Turn off or unplug items in use before replacing a blown fuse; otherwise, the replacement fuse will be immediately destroyed as well.

How fuses work

Fuses are designed to allow current through the circuit, but in the event that the current exceeds some maximum value it will burn out the wire, so that there is no longer a circuit. The current that will cause a fuse to blow is called the current rating. Fuses also have a voltage rating; this is the maximum voltage difference that the fuse can block. Once a circuit is open (broken), an applied voltage exists at the ends of the fuse, and if this voltage exceeds the voltage rating of the fuse, the air in the fuse may ionize and start conducting again, therefore leaving the circuit without a safety system.

Types of fuses

Fuses are housed in fuse boxes (see figure 1) and listed in the table below.[2]

Fuse type Description Picture
Cartridge Contains a thin conductor designed to melt at a low temperature. Once the current reaches a level that can generate enough heat to match or surpass the designed melting point, the connection will break.
A normal cartridge fuse and a slo-blo fuse[3]
Blade Contains two electrical connectors that plug into a circuit and a wire inside that will melt at a certain current.
Blade fuses[4]
Plug Screwed directly into a standard fuse socket. To learn more about this type of fuse please see EPB.
A plug fuse and its base[5]
Adapter Referred to as a rejection base (also called type-S), it requires an adapter to fit into a standard fuse socket. Once it is installed it cannot be removed. Fuses with different current ratings will have different threads; therefore, they cannot be replaced with a fuse of a different current rating. To learn more about this type of fuse please see EPB.
An adapter fuse and its base[6]

There are special fuses which handle short periods of overloads by deliberately reacting slowly, called time delay fuses. They can normally be found in a household microwave, which produces a current surge when it is turned on. See here to learn more about time delay fuses.

For Further Reading

For further information please see the related pages below:


  1. This picture contributed by someone on the team.
  2. R.T. Paynter, “Basic Electric Components and Meters,” in Introduction to Electricity, 1st ed. NJ: Prentice-Hall, 2011, ch. 3, sec. 3.6, pp. 98-107.
  3. (2014, Nov. 24). Fuses and Breakers [Online]. Available: http://hyperphysics.phy-astr.gsu.edu/hbase/electric/bregnd.html
  4. (2014, Nov. 24). Blade Type Fuses [Online]. Available: http://www.thefusecompany.net/BladeType.htm
  5. (2014, Nov. 24). Plug Fuses [Online]. Available: http://epb.apogee.net/foe/fsgofpf.asp
  6. (2014, Nov. 24). Type S/Adapter Fuses [Online]. Available: http://epb.apogee.net/foe/fsgotsf.asp

Authors and Editors

Bethel Afework, Allison Campbell, Jordan Hanania, James Jenden, Jasdeep Toor, Jason Donev
Last updated: May 18, 2018
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