Circuit breakers are designed to shut off electrical networks in case of excess current and short circuits. They protect the wiring and the consumers connected to it from overloads and contain from one to four poles. A three - pole circuit breaker is designed to protect a three-phase circuit or simultaneously three single-phase wiring. If an accident occurs on one of the lines, three poles are disconnected at once.
The device solves the following problems:
- network section protection;
- prevention of breakdown of a section of a chain;
- with the right choice, prevention of unauthorized shutdowns.
Specifications
The main characteristics of the machines are the rated breaking capacity and the cutoff speed. They are triggered by two shutdown mechanisms: electromagnetic and thermal. The first opens the circuit during a short circuit, and the second from the action of a continuous load exceeding the nominal. The machine can be used as a switch via the control key.
Rated breaking capacity
The characteristic shows the value of the maximum permissible short circuit current at which the switch is able to de-energize the wiring with the devices connected to it at least once. It is indicated on the machine body and has the meanings:
- 4.5 kA - for protection against short-circuit power lines of private housing, where the resistance of the line from the substation to the loads does not exceed 0.05 Ohm;
- 6 kA - protect the residential sector and public places where the line resistance is not lower than 0.04 ohms;
- 10 kA - used to prevent damage to power lines near the substation.
For household circuits, it is recommended to use 6 kA modification models.
Time-current characteristics
In case of uneven power consumption caused by a change in load and switching circuit devices on or off, false trips of protective devices may occur due to exceeding the rated currents. To reduce the likelihood of their operation, automata with specified time-current characteristics (VTX) are used. The parameter shows the cut-off time for a certain ratio of current to the nominal value. BTX are as follows.
- B - the electromagnetic release is activated after 0.015 seconds with a threefold increase in current relative to the nominal.
- C - the most common characteristic, when the protection is triggered when the rating increases by 5 times. Automatic machines are suitable for lighting and household appliances with moderate inrush currents.
- D - machines are designed for high inrush currents, for example, when turning on an electric boiler, electric motors and other three-phase devices. They are mainly used in industry.
Overview of circuit breakers
The machine is connected between the power source and the wiring to be protected. A three-pole circuit breaker consists of three contact pairs, where each is connected in series with thermal and electromagnetic releases. The machine disables only the phases without breaking the neutral, which does not connect to it. If there is a need to disconnect the neutral wire, four-pole models are used. Usually they are used on the main inputs.
In apartments and private houses, class C machines for moderate loads are used. The current strength is selected according to the power of the connected devices, where the threshold value is twice the nominal value in order to exclude false alarms.
Distributed products are IEK, EKF, DEK, INTEC and Kontaktor. Domestic products have sufficient reliability and reasonable prices. Widely used machines are 16 A and 25 A. Imported ones are more expensive, but well-known companies produce high-quality and reliable models. On a circuit-breaker, the automatic three - pole price of well-known companies can differ greatly, but it is quite consistent with the quality.
A protective device with a three-phase current is used at the entrance to the house and for powering professional machines with a voltage of 380 V, for example, a three-pole automatic switch 100A.
The meter should correspond to this power, if it is after the switch. Usually it is not more than 63 A. A more powerful three-pole circuit breaker is used in industry.
From the reviews and advice of experienced electricians, it follows that machines with overestimated ratings should never be used. This could result in fire or equipment failure.
A four-core wire with three phases and a working zero is connected to residential buildings. They rarely use equipment rated for 380 V. The phases in the distribution panel are separated. This results in 3 separate lines with a voltage of 220 V.
The advantage of multi-pole machines is the ability to control several lines simultaneously. By installing an automatic three-pole switch 25A on three devices of the appropriate power, it is possible to monitor each individual line. If a short circuit occurs on one of them, everything will turn off immediately. Usually, additional single-phase circuit breakers are installed on each line. When one of them fails, a three-phase will work, which increases the reliability of the system.
Automatic machines of the VA series
Domestic automatic machines are produced in the AE and VA series. The first type is obsolete and rarely used. It has a low case strength, lack of connection to a DIN rail. Products for the VA series, designed for currents up to 63 A, characteristics B, C, D and a breaking capacity of 4.5 kA, are better suited for domestic use.
Domestic three-pole circuit breaker automatic VA fully meets modern requirements, while having a price significantly lower than imported models.
If you believe the many reviews, imported models at such high prices should be ideal. But they misfire, although less often than domestic models.
Conclusion
A three-pole circuit breaker is an important part of a home electrical system. When choosing expensive models, it should be borne in mind that all other equipment should be at the same level: wiring, switches and sockets, junction boxes, lighting fixtures.
The main characteristics of the machines are always on the case on the front side. They are selected taking into account the cross-section of the wire and the magnitude of the connected load.