Automatic switches are designed to turn off electrical networks in case of excess operating current and short circuits. They protect the electrical wiring and consumers connected to it from overloads and contain from one to four poles. The three-pole circuit breaker is designed to protect a three-phase circuit or three single-phase wiring at the same time. If an accident occurs on one of the lines, three poles are switched off at once.
The device solves the following tasks:
- protection of the network section;
- preventing the breakdown of a section of the chain;
- with the right choice, prevention of unauthorized shutdowns.
Features
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 exceedingnominal. The machine can be used as a switch through the control key.
Rated breaking capacity
The characteristic shows the value of the maximum allowable short-circuit current, at which the switch is able to de-energize the wiring with devices connected to it at least once. It is indicated on the body of the machine and has the following meanings:
- 4, 5 kA - for short circuit protection of power lines of private housing, where the line resistance from the substation to 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 Ohm;
- 10 kA - used to prevent damage to power lines near the substation.
For domestic circuits, it is recommended to use 6 kA modification models.
Time-current characteristics
In case of uneven power consumption caused by load changes and switching on or off of circuit devices, 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 cutoff time at a certain ratio of current to nominal value. VTX are as follows.
- B - the electromagnetic release trips after 0.015 seconds with a threefold increase in current in relation to the nominal value.
- C - the most common characteristic, when the protection is triggered by increasing the rating by 5 times. The machines are suitable for lighting and household appliances with moderatestarting currents.
- D - machines are designed for high starting currents, for example, when turning on an electric boiler, electric motors and other three-phase devices. Mainly used in industry.
Circuit Breakers Overview
The machine is connected between the current source and the electrical wiring, which should be protected. The three-pole circuit breaker consists of three contact pairs, where each pair is connected in series with thermal and electromagnetic releases. The machine disconnects only the phases, without breaking the neutral, which is not connected 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 are used for moderate loads. 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 positives.
Products of firms IEK, EKF, DEK, INTES and "Kontaktor" are distributed. Domestic products have sufficient reliability and reasonable prices. Automatic machines for 16 A and 25 A are widely used. Imported ones are more expensive, but well-known companies produce high-quality and reliable models. For a three-pole automatic switch, the price of well-known companies can vary greatly, but it is quite consistent with the quality.
The protective device with three-phase current is used at the entrance to the house and for powering professional machines withvoltage 380 V, for example, a three-pole automatic switch 100A.
This power must correspond to the meter, if it is after the switch. Usually it is no 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 threatens to cause fire or equipment failure.
A four-core wire with three phases and a working zero is brought to residential buildings. They rarely use equipment designed for 380 V. The phases in the switchboard are separated. This results in 3 separate lines with a voltage of 220 V.
The advantage of multi-pole circuit breakers is the ability to control several lines at the same time. By installing an automatic three-pole 25A switch on three devices of the appropriate power, it is possible to control each individual line. If a short circuit occurs on one of them, all of them will turn off at once. Usually, additional single-phase switches are installed on each line. If one of them fails, the three-phase one will work, which increases the reliability of the system.
BA series machines
Domestic machines are produced in the AE and BA series. The first type is obsolete and rarely used. It has a low body strength, no connection to the DIN rail. Better for home usesuitable products of the VA series, rated for currents up to 63 A, characteristics B, C, D and a breaking capacity of 4.5 kA.
The domestic three-pole automatic VA switch fully meets modern requirements, while having a price significantly lower than imported models.
According to numerous reviews, imported models at such high prices should be ideal. But they misfire, although less often than domestic models.
Conclusion
The three-pole circuit breaker is an important part of the home electrical system. When choosing expensive models, you should take into account that all other equipment must be of 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.
