Fuses: what they are for, how they work and types

Fuses are security devices that protect the electric circuits against the damage that can be caused by an overload of electric current. Inside the fuses, there is a wire of çhumbo or andtin of varying dimensions, made to withstand a certain temperature limit and then melt, interrupting the circuit of electric current.

Lookalso: Joule Effect – what is it, solved formulas and exercises

What are fuses for?

The main purpose of fuses is make an electrical circuit safe. A sudden increase in the intensity of electrical current flowing through an electrical circuit can cause overheating, that lead to fires, burns etc.

Fuses protect sensitive electronic components from short circuits, which are the cases where the electrical resistance of an electronic circuit undergoes a sharp reduction due to the presence of impurities such as water, which contains a large amount of mineral salts.

Short circuits cause sudden increases in wire temperature and can cause fire.

Fuses are also useful to protect circuits from

overloads. The overloads come from the distribution network of electricity, however, can happen in poorly dimensioned electrical circuits.

How Fuses Work

Inside the fuses, there is a wire of çhumbo or andtin, whose dimensions (cross-sectional area and length) are calculated so that it can withstand a certain maximum electric current. If the electrical current exceeds the maximum supported value, the wire melts and the circuit is broken, without further damage being caused to the other connected components.

The choice of lead or tin as material for making fuses is not random — these metals have a low fusion point, that is, they melt at not very high temperatures.

The melting of the lead wire present inside the fuses occurs due to a phenomenonphysicist known as It is madeJoule. In the Joule effect, the passage of electric current makes the atoms in the metal's crystal lattice more agitated. The macroscopic effect of this agitation is the increasegivestemperature of the yarn.

Fuses are electrical safety devices.

At wire dimensions used inside the fuse affect the electrical resistance of that wire, which, in turn, is inversely proportional to the cross-sectional area of ​​the wire — the "thicker" the wire, the lower its resistance, consequently, the passage of electric current through this wire will dissipate less heat and the fuse will withstand higher current intensities electric. This behavior is described by 2nd law of Ohm, check out:

In the formula, R corresponds to the electrical resistance of the lead wire; ρ, the resistivity of the material; l is the length of the wire; and A is the cross-sectional area of ​​the wire.

Fuse Types

There are different types of fuses with varying electrical current ranges. However, all play the sameoccupation — interrupt the passage of electric current by fusing a conducting link.

The most common model of fuse is known as Diazed. Its main application is the safety of residential electrical circuits, whose electrical currents vary between 2 A and 63 A. This type of fuse has a cylindrical shape and is easily found in a large number of homes.

Fuse and circuit breaker

Like fuses, circuit breakers are also safety devices.

Fuses and circuit breakers play similar functions in electrical circuits, however, the latter operate somewhat differently. While fuses are discarded after the interruption of an electrical current, the breakers may continue to operate if no damage related to overheating is sustained.

Inside the circuit breakers, there is a bi-metallic blade. This type of blade contains two different glued metals. expansion coefficients, thus, when there is a sudden increase in temperature, one of the laminae dilates more than the other, bending it and disarmingOcircuit.

By Rafael Hellerbrock
Physics teacher