Low-voltage equipment includes circuit breakers.
A circuit breaker (automatic) is a device designed for short-term opening of both the electric circuit and the current flowing for a long time on it, as well as for automatic destruction of the circuits when various anomalous conditions occur in them. A switching circuit occurs between mechanically moving contacts. Automata differ in their performance, characterized by their own response time, that is, the time from the appearance of a short circuit current to the beginning of the divergence of the contacts (until the appearance of an arc). Usually this time is longer, the greater is the rated current, as with its increase in the weight of parts and the moments of their inertia increases faster than the acting forces. Its own response time decreases as the short-term current increases. All this makes it difficult to make an exact distinction between different groups.
The first group includes the most common AC and DC machines, which usually have no special requirements for implementation or these requirements are low.
Universal machines are used in industrial enterprises, in power stations and substations, on ships, etc. Installation machines are used in the same place as universal ones, and, moreover, in public buildings and dwellings for the protection of lighting networks. Installation machines that meet all the requirements for the installation of products and specially designed for installation in apartments, sometimes called household machines.
The second group includes high-speed automata, as a rule, is produced at rated constant currents from 500 to 10 000 A and have their own tripping time at high currents within. Their characteristic feature is that the whole structure is subject to the requirement for increasing productivity, which is necessary to protect the units, converting alternating current into direct current, which are always very sensitive.
The first two groups include automata that commute circuits in which there is an anomalous phenomenon. The third group includes the quenching fields of the automaton, which turn off the excitation winding of the generators during a short circuit in the main generator circuit.