What is a short circuit in an electrical circuit?

Anyone whose work is related to the maintenance of electrical equipment, very well knows about the troubles that are fraught with a short circuit (AC). Sometimes it is considered that it is a damage. This is not true. A short circuit is a process, or, if you prefer, an emergency operation of any part of the electrical installation. But the consequences of it do lead to damage. A commonly accepted definition is: "A short circuit is the direct connection of two or more points of an electrical circuit with different potentials. It is an abnormal (unintended) mode of operation. "

To understand what is happening in the circuit at the moment when there is a short circuit, it is necessary to recall the principles of the functioning of the contour elements. Imagine a simple circuit consisting of a power source, two conductors and a load (for example, a light bulb). Under normal conditions, there is a directed movement of charged elementary particles in the conductor, caused by the constant action of the electromotive force of the source. They travel from one pole of the source to the other through two sections of the wire and a lamp. Accordingly, the lamp emits light, since the particles perform a certain work in it.

With alternating current, the direction of motion is constantly changing, but in this case it is not a matter of principle. The number of electrons passing through a certain section of the circuit per unit time is limited by the resistance of the lamp, conductors, and the source of the EMF. In other words, the current does not grow infinitely, but corresponds to the steady state.

But for some reason, the insulation on the circuit is damaged. For example, the lamp flooded with water. In this case, its electrical resistance decreases. As a result, the current flowing through the circuit is limited by the total resistance of the power source, wires and water "isthmus" on the lamp. Usually this amount is so insignificant that it is not taken into account in the calculations (special calculations are an exception).

The result is an almost infinite increase in current, determined by the classical Ohm's law. In this case, the power of a short circuit is often mentioned. It is determined by the limiting value of the electric current, which is able to give out the power source before failure. By the way, that's why it is forbidden to connect wiring (short-circuiting) the opposite contacts of the batteries.

Although in the example we consider the elimination of the resistance of the lamp from the circuit due to the water hit on it, the causes of the short circuit are plentiful. For example, if we talk about the same scheme, then kz. It can also occur if the insulation of at least one wire is broken and it comes into contact with the ground. In this case, the current from the power source will follow the path of the least resistance, that is, to the earth, which has a huge capacity. Damage to the insulation of two wires at the same time and their contact will lead to the same result.

The above can be summarized: k.s can be with the earth and without it. It does not affect the processes that occur.

What kind of damage was discussed at the beginning of the article? As is well known, the higher the value of the current flowing through the sections of the circuit, the greater their heating. With sufficient power of the source for short circuits. Some parts of the chain simply burn out, turning into copper dust (for copper elements).

Short circuit protection is quite simple and effective. Reports of faults due to short-circuiting arise, primarily due to improperly selected parameters of the protection apparatus, incorrect selectivity. If it is a household circuit 220 V, then use automatic switches. In them, with an excessive current increase, an electromagnetic release inside the circuit breaks the circuit.