Circuit breaker

A circuit breaker is a switching and protective device that turns on, conducts and turns off the electric current under normal parameters of the electrical circuit, as well as the current that conducts and automatically turns off for a certain time in emergency situations - e.g. , in case of short circuit.

The abbreviation MCB, often found in electrical engineering, is shortened from the English miniature circuit breaker - "miniature circuit breaker". Often, instead of "miniature" in this abbreviation, the word "modular" is used.

Modular circuit breakers (hereinafter referred to as MCB) are intended for infrequent operational switching (on/off) of low voltage electrical circuits, protection against load currents and short circuit overcurrent (hereinafter short circuit).

MVS are installed in switchboards at the entrance to the site (industrial/commercial building, residential building, apartment, etc.), as well as in metal and plastic boxes at the beginning of the protected line. In the electrical circuit, the MVS is connected in series with the protected device.

In the normal state of the electrical network, after switching on the MV, a current, not greater than the nominal, constantly flows through it. In emergency situations - prolonged exposure to overload currents, occurrence of short-circuit currents - the MCB will automatically disconnect the load from the power supply network for a short time, fulfilling its protective function.

Unlike its predecessors fusible fuses (PF), which perform a one-time protective function, the MCB is a protective switching device with multiple action. After an emergency situation (short circuit, exposure to a significant load current), PP is unsuitable for further work, because its protective element melts into quartz sand. After the protective element (bimetallic plate, see below) has hardened, the MSV can be put back into service. However, it should be remembered that each subsequent emergency mode and operational switching under voltage in normal mode will gradually reduce its operational resource. Once every six months, it is recommended to tighten the screw terminals of the MCV to neutralize the weakening of the mechanical compression of the contact connection, especially in situations where wires with aluminum cores are connected to the MCV.

Structural elements:

*Body made of non-flammable material;
*Screw terminals with protection against incorrect connection (for example, MSV 6 kA, e.mcb.pro) — for wire/cable connection;
*Clamp (latch) — for mounting on a DIN rail;
*Control handle — for on/off;
*Status indicator — for visual indication of the status of the group of contacts;
*Movable and fixed contacts - for switching electrical circuits;
*The release mechanism - to turn off the MSV;
*Electromagnetic release coil with core - affects the release mechanism in the event of a short circuit;
*Bimetallic plate of the thermal release - affects the release mechanism at overload currents;
*Arc extinguishing chamber - for extinguishing the arc.
In addition, there are spark-extinguishing plates in the housing of the MSV, which protect the housing from burning; the body itself has an opening for the discharge of overpressure and products of gas arc combustion in the event of a short circuit, fastened with rivets that increase its mechanical strength. The handle of the MSV has a comfortable ergonomic shape.

The main criteria for classifying MSW:

*Number of poles: one-, two-, three- and four-pole;
*Width of the post: 1 mounting module – 18 mm; 1.5 modules – 27 mm;
*The value of the rated current, which is continuously carried out by the MV under normal conditions without deterioration of its working properties;
*Time-current performance characteristics of the electromagnetic release (type: B, C, K, D).
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