Today there are thousands of different fuse designs which have specific current and voltage ratings, breaking capacity, and response times, depending on the application.

The time and current operating characteristics of fuses are chosen to provide adequate protection without needless interruption.

When a damaged live wire makes contact with a metal case that is connected to ground, a short circuit will form and the fuse will melt.

[1] A variety of wire or foil fusible elements were in use to protect telegraph cables and lighting installations as early as 1864.

The fuse element is made of zinc, copper, silver, aluminum,[citation needed] or alloys among these or other various metals to provide stable and predictable characteristics.

The element must not be damaged by minor harmless surges of current, and must not oxidize or change its behavior after possibly years of service.

The fastest blowing fuses are designed for the most sensitive electrical equipment, where even a short exposure to an overload current could be damaging.

Since the I2t rating of the fuse is proportional to the energy it lets through, it is a measure of the thermal damage from the heat and magnetic forces that will be produced by a fault end.

Fuses for small, low-voltage, usually residential, wiring systems are commonly rated, in North American practice, to interrupt 10,000 amperes.

Fuses for high-voltage equipment, up to 115,000 volts, are rated by the total apparent power (megavolt-amperes, MVA) of the fault level on the circuit.

Fuse markings[9] will generally convey the following information, either explicitly as text, or else implicit with the approval agency marking for a particular type: Fuses come in a vast array of sizes and styles to serve in many applications, manufactured in standardised package layouts to make them easily interchangeable.

Fuses for low voltage power circuits may have bolted blade or tag terminals which are secured by screws to a fuseholder.

When the fuse element blows, the indicating pin extends to activate the micro switch or relay, which, in turn, triggers an event.

All fuses of different technologies tested to meet IEC standards will have similar time-current characteristics, which simplifies design and maintenance.

There are several different types of automotive fuses and their usage is dependent upon the specific application, voltage, and current demands of the electrical circuit.

A circuit breaker at 115 kV may cost up to five times as much as a set of power fuses, so the resulting saving can be tens of thousands of dollars.

Pole-mounted distribution transformers are nearly always protected by a fusible cutout, which can have the fuse element replaced using live-line maintenance tools.

Medium-voltage fuses are also used to protect motors, capacitor banks and transformers and may be mounted in metal enclosed switchgear, or (rarely in new designs) on open switchboards.

Large power fuses use fusible elements made of silver, copper or tin to provide stable and predictable performance.

High voltage expulsion fuses surround the fusible link with gas-evolving substances, such as boric acid.

The associated high pressure (often greater than 100 atmospheres) and cooling gases rapidly quench the resulting arc.

The blown fuse must be replaced with a new device which is less convenient than simply resetting a breaker and therefore likely to discourage people from ignoring faults.

Current-limiting fuses operate so quickly that they limit the total "let-through" energy that passes into the circuit, helping to protect downstream equipment from damage.

In a multi-phase power circuit, if only one fuse opens, the remaining phases will have higher than normal currents, and unbalanced voltages, with possible damage to motors.

Renewable fuses (rewirable or cartridge) allow user replacement, but this can be hazardous as it is easy to put a higher-rated or double fuse element (link or wire) into the holder (overfusing), or simply fitting it with copper wire or even a totally different type of conducting object (coins, hairpins, paper clips, nails, etc.)

One form of fuse box abuse was to put a penny in the socket, which defeated overcurrent protection and resulted in a dangerous condition.

Some Wylex standard models were made with an RCD instead of the main switch, but (for consumer units supplying the entire installation) this is no longer compliant with the wiring regulations as alarm systems should not be RCD-protected.

This process is called "coordination" and may require the time-current characteristics of two fuses to be plotted on a common current basis.

So-called self-resetting fuses use a thermoplastic conductive element known as a polymeric positive temperature coefficient (PPTC) thermistor that impedes the circuit during an overcurrent condition (by increasing device resistance).

When the surrounding temperature gets too high, the composition melts and allows the spring contact mechanism to break the circuit.