Circuit breakers

Circuit breakers

What are circuit breakers?

Automatic circuit breakers (also known as automatic fuses, or colloquially fuses) are electromechanical components in the electrical circuit that protect the power transmission and power line, as well as the consumers connected to it, from overload or short circuits. Its main function is to interrupt the phase line when a problem occurs, unlike the ordinary fuse which is used once, the circuit breaker is reset manually or automatically. The abbreviation MCB, common in electrical engineering, is an abbreviation for English. miniature circuit breaker - "miniature circuit breaker." Often, instead of "miniature" in this abbreviation, the word "modular" is used. Circuit breakers are installed in switchboards at the entrance to the site (industrial/business building, residential building, apartment, etc.), as well as in metal and plastic boxes at the beginning of the protected line. In the electrical circuit, circuit breakers are connected in series with the protected device.

Learn more

Автоматични прекъсвачи1 | Енекст България — Circuit breakers - Modular circuit breaker e.mcb.stand.60.1.C25, 1p, 25A, C, 6 kA

In the normal condition of the electrical network, after switching on the automatic circuit breaker , a current that does not exceed the nominal current flows through it. In emergency situations - prolonged exposure to overload currents, occurrence of short-circuit currents - circuit breakers will automatically disconnect the load from the supply network for a short time after it has fulfilled its protective function.

Unlike their predecessors, fuses (FP), which perform a single-use protective function, circuit breakers are reusable protective switching devices. After an emergency situation (short circuit, exposure to a significant overload current), F P is unsuitable for further operation, because its protective element is melted into quartz sand. After the protective element (bimetallic plate, see below) has cooled, the circuit breakers can be put back into service. However, it should be remembered that each subsequent emergency mode and operational switching under voltage in normal mode gradually reduces its service life. Once every six months, it is recommended to tighten the screw terminals of the circuit breakers to neutralize the weakening of the mechanical compression of the contact connection, especially in situations where wires with aluminum conductors are connected to the circuit breakers .

Автоматични прекъсвачи2 | Енекст България — Circuit breakers - Modular circuit breaker e.industrial.mcb.100.1.C25, 1 p, 25A, C, 10kA

Structure of circuit breakers

Body made of non-combustible material;
Screw terminals with protection against false connection (e.g. automatic circuit breaker 6 kA, e.mcb.pro) - for connection of wire / cable;
Clamp (latch) - for Din-rail mounting;
Control handle - to turn on / off;
Status indicator - for visual indication of the status of the contact group;
Movable and fixed contacts - for switching the electrical circuit;
Release mechanism - to turn off the circuit breaker;
Electromagnetic release coil with a core - acts on the release mechanism in the event of a short circuit;
Bimetallic thermal release plate - affects the release mechanism at overload currents;
Arc extinguishing chamber - for extinguishing the arc.

In addition, spark-extinguishing plates are located in the housing of the circuit breakers , which protect the housing from burning; the body itself has a hole for the outlet of overpressure and gaseous products of arc combustion during a short circuit, fastened with rivets, which increase its mechanical strength. The handle of the circuit breakers has a comfortable ergonomic shape.

How do circuit breakers (fuses/fuses) work?

The operation of all circuit breakers is similar, but the details vary greatly depending on:

voltage class
the magnitude of the current
fuse type

Автоматични прекъсвачи3 | Енекст България — Circuit breakers - Modular circuit breaker e.mcb.pro.60.1N.C25.thin, 1p+N, 25A, C, 4.5kA

For a circuit breaker to operate, a fault must first occur. In small mains and low voltage circuit breakers this happens within the device itself, usually using the process of heating when an electric current flows or magnetic effects of the electric current. High current or high voltage circuit breakers are usually equipped with protective relay pilot devices to sense a fault condition and operate the opening mechanism. They usually require a separate power source, such as a battery, although some high-voltage circuit breakers are self-contained with current transformers, protective relays and an internal control source.

What is the service life of circuit breakers and fuses?

Circuit breaker contacts must be able to withstand the load current without overheating and must also withstand the heat caused by the arc produced when the circuit is broken (opened). Contacts are made of copper or copper alloys, silver alloys and other highly conductive materials. The service life of the contacts is limited by erosion of the contact material due to wear of the contacts and due to wear of the mechanical element. Miniature circuit breakers and molded case circuit breakers are usually discarded when the contacts are worn, but high power circuit breakers and high voltage circuit breakers have replaceable contacts. There are various methods of dealing with arcing caused by opening the contacts.

Автоматични прекъсвачи4 | Енекст България — Circuit breakers - Modular circuit breaker e.industrial.mcb.100.2.C6, 2 p, 6A, C, 10kA

How are circuit breakers and fuses selected?

Circuit breakers, in addition to being selected for the rated current that will flow through them, have a parameter and a maximum short-circuit current that they can safely break. In the case of a short circuit, when the electrical contacts open to interrupt the huge current that is passing, an arc forms between the two poles of the open contacts, which would allow the current to continue to flow. This condition can create conductive ionized gases and molten or vaporized metal, which can cause further arcing or create additional short circuits, potentially exploding the circuit breaker, equipment and installation in which it is installed. Typical household circuit breakers are designed to break short-circuit currents on the order of 10 kA (10,000 A)

What are the standards for circuit breakers and fuses?

International standards IEC 60898-1 and European standard EN 60898-1 define the rated current of a circuit breaker for installation in low-voltage networks as the maximum current that the circuit breaker is designed to withstand continuously (at an ambient temperature of 30 °C). Usually the preferred values for the rated current are 1A, 2A, 4A, 6A, 10A, 13A, 16A, 20A, 25A, 32A, 40A, 50A, 63A, 80A, 100A, and 125A. The circuit breaker is indicated by the rated current in amperes , but excludes the A symbol on the device. Instead, the ampere figure is preceded by the letter B, C, D, or K which indicates the instantaneous tripping current - i.e. the minimum value of current that causes the circuit breaker to trip without intentional delay (ie for less than 100 ms) expressed in terms of In: for curve B above 3 In, for curve C from 5In to 10In, for curve D from 10In to 20In etc.

Circuit breakers - Modular circuit breaker e.mcb.pro.60.2.C 63 new, 2p, 63А, C, 6kА new

Types of circuit breakers and fuses:

Автоматични прекъсвачи6 | Енекст България — Circuit breakers - Modular circuit breaker e.mcb.stand.45.3.C32, 3p, 32A, C, 4.5 kA

Types of circuit breakers and fuses according to the number of phases they interrupt:

single-phase circuit breakers
single-phase circuit breakers with zero interruption
three-phase circuit breakers, etc.

Автоматични прекъсвачи7 | Енекст България — Circuit breakers - Modular circuit breaker e.mcb.pro.60.3.K 63 new, 3p, 63А, K, 6kА new

Automatic circuit breakers and fuses from Enext

The company Ennext Bulgaria Ltd. offers an extremely rich variety of automatic circuit breakers and fuses, fuses, our production with a high level of quality, and this does not prevent us from maintaining incredibly low prices.