Circuit breakers are devices through which the power line is protected from the negative effects of high current, which can cause overheating of the wires, melting of the insulation and ignition.
Why do we need circuit breakers
There are many reasons why the current in the network can exceed normal values. This is mainly due to excessive load, when the total power of the connected devices exceeds the amount that the cable cross section can withstand. In this case, the machine does not turn off immediately, but only after the temperature of the wire reaches the set level.
If a short circuit occurs in the network, this leads to a multiple increase in current power in an instant, so the circuit breaker immediately responds to the situation and blocks the supply of electricity.
What are the machines
There are three categories to which a circuit breaker may belong. Each of them is designed for a specific load, and the differences between the types are in the features of the design used.
- Modular devices can most often be found in household networks connected to a power supply network with insignificant currents. In the vast majority of cases, they differ in the presence of one or two poles.
- Cast ones are used in industrial networks, where the current power reaches 1000 A. They got their name because their main feature is the use of a molded case.
- Air circuit breakers can have up to four poles, with the ability to withstand currents up to 6300 A. In this regard, they are installed only in electrical circuits to which high-power installations are connected.
There are also differential automata, these are ordinary switches with RCDs in their design.
Release devices and their variants
The release is a key element of any circuit breaker. It carries the function of blocking the power supply if the current exceeds the permissible value. In this case, there are two varieties of such devices that an automatic circuit breaker can be equipped with - thermal or electromagnetic.
The latter are distinguished by the fact that with their help an almost instantaneous operation of the protective system is achieved, and the area is immediately de-energized as soon as the occurrence of a short circuit is detected. The design includes a coil with a core, which, under the influence of a strong current, is pulled inward, because of which the tripping element is constantly triggered.
A key component of the thermal release is a bimetal plate. If the machine detects the passage of current through it, the force of which exceeds the set value, the temperature of the plate rises, and due to this, it catches a disconnecting element, which instantly disconnects the network from the supply. The time period for which this element will work will directly depend on how much force the current passing through the plate has.
As an additional device, zero trip units are often installed, which trip the circuit breaker if the voltage has an indicator below the permissible limit.
There are remote-type devices that not only block, but also return the energy supply without the need to independently approach the electrical panel. However, these options significantly increase the overall price of the equipment.
The difference between machines on the number of poles
The circuit breakers are equipped with up to four poles. To purchase a suitable device, it is enough to understand the types of electric machines, the purpose and characteristics of each of them:
- One pole. Designed for safety in the electrical network, providing power to conventional outlets and lighting in the house. Mounted on a phase wire, excluding the capture of zero.
- Two poles. They are connected to the circuit, which provides power for household appliances, characterized by high energy consumption. This category includes electric stoves, washing machines and others.
- Three poles. They are installed in semi-industrial networks that provide power to powerful devices like borehole pumps or installations for a car workshop.
- Four poles. Provide network security against overloads and short circuits, allowing you to connect four cables to it at once.
Devices are selected only depending on their area of application.
Circuit Breaker Parameters
The characteristics of circuit breakers is another indicator by which they differ from each other. First of all, the masters pay attention to how protective equipment is sensitive to current surges. It is enough to look at the corresponding marking to understand how the device will respond to an increase in current strength. Some immediately turn off access to power, while others are delayed.
Depending on the sensitivity, the marking also changes:
- A. The most sensitive and efficient devices that instantly turn off the power supply as soon as an increased load is detected. They are not used in household networks. The main field of application are circuits providing power to precision equipment.
- B. When it is detected that the current exceeds the rated value of the force, the machine turns off the power with a slight delay. In the predominant majority of cases, the scope of application of these devices is the lines into which expensive household appliances are connected.
- C. The most popular version of machines for domestic use. When such equipment registers an excess of current, they do not immediately turn off the power, but with a certain delay. Due to this, if the difference is insignificant, the load can normalize itself, without requiring a forced shutdown of the entire room.
- D. They have the lowest sensitivity, because of which the main scope of their application is electrical panels, which are on the way to the building. In other words, these shields provide a kind of safety net for apartment devices: if the latter for some reason do not work after a critical situation is detected, the general network is turned off by these devices.
There are also special machines for networks with a load above 1000 volts. Such circuit breakers are complex equipment that is custom-made for the desired voltage class. In most cases, they are mounted on transformer substations. They must be reliable, safe, easy to operate, quickly respond to accidents and be relatively silent during operation.
How to choose a circuit breaker
It is believed that the most reliable option of a circuit breaker is a device that can withstand the maximum load and provide the room with the most effective protection.If you follow this logic, you can use automatic machines in any networks, and thus save yourself from most problems, but in practice the situation is somewhat different. Depending on the parameters of a particular circuit, the type of switch that is best installed in it will depend. If you make a mistake in choosing a circuit breaker, in the end it can turn out very negatively.
If a device that is designed to operate in conditions of increased power is connected to an ordinary household power supply network, it will not turn off the power even when the current strength substantially exceeds all permissible norms. At the same time, the temperature of the insulating layer will increase significantly and become destructive for the cable, but the rating of the circuit breaker will not be exceeded, therefore, the machine will perceive such a situation as ordinary. Shutdown will occur only after a short circuit occurs due to melting of insulation in the network, but this situation is already fraught with fire.
If the permissible power of the machine, on the contrary, does not reach that which the power line can withstand, it is almost impossible to achieve normal operation of the circuit. After connecting several devices, electricity will be knocked out immediately, as a result, due to the constant influence of a large current, it will break due to “sticking” of the contacts.
A circuit breaker is an extremely important device that protects the power supply from the risk of damage due to high current. The operation of networks that do not have automatic devices is prohibited in accordance with the Electrical Installation Rules. In this regard, it remains only to choose the type of switch that will provide reliable network protection.
