Stable operation of electrical equipment is ensured by the rated current parameters in the network. With overloads and short circuits, the wiring is destroyed, there is a risk of damage to electrical appliances. To ensure the security of local networks, an automatic three-pole 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:
- disables rated current in manual mode;
- prevents breakdown in the chain;
- automatically breaks emergency or overloaded lines;
- prevents unauthorized shutdown.
Such devices are massively used in enterprises where a voltage of 380 volts is needed to power powerful units, machine tools and other equipment. The 3-pole circuit breaker trips when the rated load increases in any of the three wires of the circuit and simultaneously turns them off.
To protect household networks, automatic machines of a modular design are used.
Characteristics of the machine
In fact, this is a triple version of a single-pole device for an electric circuit with three phases. A design feature is the presence of protective functions at each individual pole. The main characteristics are the permissible short circuit current at which the switch trips, and the cutoff speed.
There are two mechanisms for disconnecting - electromagnetic and thermal. In the event of a short circuit, the electromagnet opens the circuit. Thermal is triggered during continuous, exceeding the rated load. Also, the device is a switching device. If necessary, the machine can be used to turn on or off the current.
By design, the device has the following elements:
- management mechanism;
- power contacts;
- arc extinguishing unit;
- release;
- pole terminals for connecting wires.
Functional units are located in the housing. There are loose contacts in the appliance cover. In a kinematic way, they are connected to the traverse of the main contacts. The case itself and the cover are made of plastic or textolite. Material does not pass electric current.
Principle of operation
In working condition, the switch contacts are in the closed position. The rated current flows freely through the circuit breaker. If the load exceeds the specified parameters, an automatic shutdown occurs. In case of a short circuit, the machine shuts off the network instantly.
The cause of the overload may be the simultaneous connection of consumers when their total capacity exceeds the calculated capacity of the network. For example, the simultaneous inclusion of a washing machine and a boiler, air conditioning, electric stove. Circuit disconnection due to overload lasts longer than a specified period.
If necessary, the device can be turned off manually. In an emergency, even if the user holds the handle to turn on, the machine will still disconnect all poles.
Rated breaking capacity
With a short circuit, the current strength increases sharply. The electromagnetic release actuates the levers of the mechanism. Safety switch trips. De-energizing the wiring occurs in 0.02 seconds, it does not have time to heat up.
The presence of an arcing chamber does not allow the passage of current through the plasma channel of the charge, and does not allow a fire to develop. Thus, the contacts are protected from sticking and burnout, and the emergency shutdown time is minimal.
Choosing a model, you need to focus on what kind of power lines you need an automaton to power off the network with devices connected to it. On the case there is a parameter indicating the amount of current that the machine is able to withstand during a short circuit:
- 4.5 kA is enough for outgoing lines in apartment panels
- cable included in the shield - 6 kA;
- for switchgears at the input of the power line to the house - 10 kA.
It is important to consider wiring resistance. Aluminum cable has more resistance than copper. Therefore, a 4.5 kA circuit breaker is suitable for it, and 6 kA for a copper circuit breaker. According to Ohm's law, the current strength in a conductor is inversely proportional to its resistance.
Time-current characteristics
The operation of the electromagnet is aimed at emergency current. The device does not respond if the excess occurred due to overloads associated with consumers. In this case, a bimetal release is used to protect the wiring. Over a period of time, the plates heat up. One of them bends and sets in motion a trip mechanism.
Uneven power consumption, increase in load with exceeding 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 three-fold increase in current strength, the device trips after 0.015 seconds.
- C - the machine switches off if the current is 5 times higher than the rated value.
- D - used to protect an electric boiler, engines and other devices.
During short-term overload, for example, during the start of the motor, the plate does not have time to heat up. The current parameters return to normal and the switch continues to operate.
You can change the default settings if necessary. But there must be confidence that the wiring can withstand the increase in the load of the local network.
Overview of circuit breakers
The device is selected taking into account the voltage, current and temperature. General specifications must be indicated on the housing.
- Configuration - single, double, or triple 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 devices of all configurations.
- The release voltage is from 24 to 440 volts.
- They can work at ambient temperature from -25 ° to + 60 °.
Automatic machines of the VA series are intended for electric lines with alternating current with a frequency of 50/60 Hz. Rated voltage up to 690 V, with a rated current of not more than 6300 A. They are used as protection in power supplies and current distribution circuits, on-line 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.
The three-pole circuit breaker 100A is designed to protect against short circuits, overloads and infrequent switching. It is used in industrial construction and for household power supply. It has the following characteristics:
- rated current 100 A;
- trip current 10 kA;
- maximum AC voltage 230/400 V;
- constant 60 V;
- wire cross section 25 mm2;
- fastening - DIN rail.
Compact dimensions allow you to mount the device 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 automatic machine 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 works with a short-circuit current of up to 4.5 kA, wire cross section is from 4 to 25 mm2. Mechanical wear resistance up to 10 thousand cycles, switching 4000. Protection against ingress of solids 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 current limitation class is indicated on the case - the second or third. If not marked, this is a first class 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.
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- 25A - protection of input distribution devices
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- C63 - protection of household and lighting devices
A three-pole circuit breaker is an important part of the electrical network. It is selected taking into account the magnitude of the connected load and the cross section of the wire. To do this, all specifications are indicated on the front of the case. When choosing an expensive device, it is important to understand that the rest of the equipment must have the same level of quality.
