What is the short-circuit current?

Chemical sources of current (batteries and batteries) are so firmly embedded in our lives, becoming something familiar and natural that many of their owners do not even read what is written on their packages and packages. And it's completely vain, because there is a very curious warning - "Do not close." Anyone who is at least familiar with the basics of electrical engineering, knows well what the short-circuit current is and why it is impossible to short-circuit the contacts.

Any current source always has two poles: positive and negative (+ and -) for direct current, as well as phase and earth (zero, mass, sometimes another phase) for alternating current. The motion of charged particles is possible only if these poles are connected by a conductive material. If an electric appliance is connected to the conductor break, then a certain work will be performed by the current passing through the circuits of the device. The main feature is that the circuits of this electrical appliance do not allow electrons to pass through them unimpeded, therefore it can always be assumed that there is a resistance (load) limiting the maximum flow of particles (short-circuit current).

For simplicity of understanding, we give an example of water flowing through a channel (conductor). The beginning of the flow is one pole, and its end is the second pole. In the middle of the channel are the blades of the water mill (load), rotated by the movement of water (current). It is obvious that the flow velocity is always limited by the resistance of the blades. But what happens if the mill disappears? Water, not experiencing resistance, rushes through the channel at the maximum speed that the source can provide (short circuit). At the same time, the probability of damage by a turbulent flow of both the source and the channel is very high. In electricity, the intensity of the flow is the short-circuit current strength .

The same thing happens in electricity. If, for any reason, the resistance of the circuit begins to tend to zero, a short-circuit current occurs. The conductor is then heated, and the current source is damaged. This mode of operation of the electrical installation is emergency and requires immediate elimination. Typically, a circuit breaker is installed in the circuit, breaking the circuit if it detects a short-circuit current. By analogy with water: the channel is blocked and the flow disappears. With the power source turned off, it is quite easy to determine the fact of a short circuit in an arbitrary section of an electrical circuit . For this purpose a special device (multimeter) measures the resistance value between the points of application of the probes. The indirect method is based on the use of an indicator or a continuum: if it is known that there should be no poles on the verified section of direct contact, then check this condition. In power units, this is more rational than measuring the exact resistance of a multimeter.

By the way, that's why you can not connect the poles of the batteries. Although their power is not enough to significantly damage the conductor, but the chemical components that are inside become short-circuited quickly degrading, reducing the overall resource life of the source.

When studying electrical safety, the term "short-circuit shock current" is often used. It determines the highest value of the current appearing as a result of the occurrence of a short circuit. In alternating current circuits , its maximum value will be reached after a half-cycle (0.01 s for a frequency of 50 Hz).

It should be noted that there are special electrical devices for which the short-circuit mode is not emergency, but normal. A striking example - welding machines, in which the visible arc is just a short-circuit current.