Stable operation of electrical equipment is ensured by the nominal parameters of the current in the network. With overloads and short circuits, the electrical wiring is destroyed, there is a threat of breakdown of electrical appliances. To ensure the safety of local networks, a three-pole automatic switch is installed.
Where are the switches used?
The machine is designed to disconnect the electrical network in case of exceeding the operating current or in the event of a short circuit. A three-pole switch is installed to protect a three-phase circuit, or three single-phase wiring. The device solves the following tasks:
- disconnects the rated current in manual mode;
- prevents breakdown at the section of the circuit;
- automatically breaks off emergency or overloaded lines;
- prevents unauthorized shutdown.
Such devices are massively used in enterprises where a voltage of 380 volts is required to power powerful units, machine tools and other equipment. A 3-pole circuit breaker is triggered when the rated load in any of the three wires of the circuit rises and at the same time disconnects them.
To protect household networks, modular machines are used.
Machine characteristics
In fact, this is a triple version of a single-pole device for an electrical circuit with three phases. The design feature is the presence of protective functions at each individual pole. The main characteristics are the permissible short-circuit current at which the circuit breaker trips and the cut-off speed.
There are two mechanisms for shutdown - electromagnetic and thermal. In the event of a short circuit, the electromagnet opens the circuit. Thermal is triggered at continuous, exceeding the rated load. Also, the device is a switching device. If necessary, the machine can be used to turn the current on or off.
By design, the device has the following elements:
- control mechanism;
- power contacts;
- electric arc extinguishing unit;
- release;
- pole terminals for connecting wires.
Functional units are located in the body. There are free contacts in the cover of the device. They are connected in a kinematic way with the traverse of the main contacts. The body and cover itself are made of plastic or PCB. The material does not allow electric current to pass through.
Principle of operation
In the operating state, the contacts of the switch are in the closed position. The nominal allowable current freely passes through the circuit breaker. If the load exceeds the specified parameters, an automatic shutdown occurs. In the event of a short circuit, the machine turns off the network instantly.
The reason for the overload may be the simultaneous connection of consumers, when their total capacity exceeds the rated capacity of the network. For example, the simultaneous inclusion of a washing machine and a boiler, air conditioner, electric stove. The disconnection of the circuit due to overload lasts longer than the specified period.
If necessary, the device can be turned off manually. In an emergency, even if the user holds the handle to close, the machine will still disconnect all poles.
Rated breaking capacity
The presence of the arc-extinguishing chamber does not allow the passage of current through the plasma charge channel, does not allow a fire to develop. Thus, the contacts are protected from sticking and burning out, and the time of the emergency shutdown of the network is minimal.
When choosing a model, you need to focus on what power lines you need an automatic machine for in order to de-energize the network with devices connected to it. On the case there is a parameter indicating the amount of current that the machine can withstand in case of a short circuit:
- 4.5 kA is enough for outgoing lines in apartment shields;
- cable included in the shield - 6 kA;
- for switchgears at the entrance of the power line to the house - 10 kA.
It is important to consider the resistance of the wiring. Aluminum cable has more resistance than copper cable. Therefore, a 4.5 kA circuit breaker is suitable for it, and 6 kA for a copper one. According to Ohm's law, the current in a conductor is inversely proportional to its resistance.
Time-current characteristics
Uneven power consumption, an increase in load with excess of the rated current leads to the operation of the machine. There are devices with specified time-current characteristics. They are marked as follows:
- B - with a threefold increase in the current strength, the device is triggered in 0.015 seconds.
- C - the machine turns off if the current is 5 times the nominal value.
- D - used to protect an electric boiler, motors and other devices.
In case of short-term overload, for example, when starting the motor, the plate does not have time to heat up. The current parameters return to normal and the breaker continues to operate.
You can change the default settings if necessary. But you must be sure that the wiring will withstand the increased load on the local network.
Circuit breakers overview
- The configuration is one-, two-, or three-pole.
- DC voltage, in accordance with the design - 240, 440, 600 volts.
- AC voltage 380, 380, 660.
- Rated current from 0.6 to 100 amperes, for all instrument configurations.
- Release voltage from 24 to 440 volts.
- They can operate at ambient temperatures from -25 ° to + 60 °.
Automatic machines of the VA series are designed for electric lines with alternating current with a frequency of 50/60 Hz. Rated voltage up to 690 V, at rated current no more than 6300 A. Used as protection in power supplies and current distribution circuits, operational switching on and off of electrical circuits.
Devices are produced for different protective characteristics and rated currents. The most famous foreign brands are ABB, Schneider Electric, Legrand. The best domestic manufacturers KEAZ, IEK, CONTACTOR.
Three-pole automatic switch 100A is designed for protection against short circuits, overloads and infrequent switching. It is used in industrial construction and for household power supply. Has the following characteristics:
- rated current 100 A;
- tripping current 10 kA;
- maximum AC voltage 230/400 V;
- constant 60 V;
- wire section 25 mm2;
- mount - DIN rail.
Compact dimensions allow the device to be mounted in an electrical panel on a standard rail. Designed for 10 thousand switching cycles, this is enough for several years of intensive work.
Three-pole circuit breaker 25a is designed to protect input-distribution devices in residential and public buildings.It is connected to a network with an alternating voltage of 12-230 V. It operates at a short-circuit current of up to 4.5 kA, wire cross-section from 4 to 25 mm2. Mechanical durability up to 10 thousand cycles, switching 4000. Protection against ingress of solid bodies IP20.
The c63 machine can be used to protect the network with the connection of heating and lighting devices. And also for networks with transformers, motors and electronic devices. Switching capacity 4.5 kA or 6 kA. The class of current limitation is indicated on the case - the second or third. If there is no mark, it is a Class 1 device. The wiring after the machine must be made of copper wire with a cross section of at least 16 mm2, or aluminum 25 mm2.
A three-pole circuit breaker is an important part of the electrical network. It is selected taking into account the size of the connected load and the wire cross-section. For this, all characteristics are indicated on the front side of the case. When choosing an expensive device, it is important to understand that the rest of the equipment should be of the same quality level.
