When you are planning an electrical installation in a company or an apartment, you cannot do without circuit breakers. They protect consumer property and human life from unexpected situations. A professional electrician should know how to choose the right circuit breakers for reliable and safe operation of the power grid, how to make a selection of circuit breakers on the power used by the load and other parameters.
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What a circuit breaker is for
A circuit breaker or automatic circuit breaker in simple terms is needed to prevent overheating of the insulation of wires and protect the electrical circuit from short-circuit current. Moreover, with a circuit breaker, maintenance of electrical lines is more convenient, because at any time you can turn off the circuit at the desired section.
To perform these tasks, the circuit breaker is equipped with a thermal and an electromagnetic release. Each circuit breaker is designed for a certain rated current and time-current characteristic. The maximum operating current of the line depends on these parameters.
When electric current flows through the wires, the wire heats up and the greater the value, the greater it is. If a circuit breaker is not installed, at a certain value of current the insulation can begin to melt, which can cause a fire.
What kinds of circuit breakers are available
Circuit breakers for apartments are modular devices. This means that they can be installed in apartment distribution boards on a special DIN-rail, with the same dimensions for different manufacturers and the same number of poles.
Non-modular circuit breakers are also found in electrical cabinets at the enterprise or transformer substations. They are distinguished by their large overall dimensions and rated current. They look like the picture below.
According to the number of poles, circuit breakers are divided into single-pole, two-pole, three-pole and four-pole. Most often, a single-phase electrical network is designed so that a single-pole circuit breaker breaks a phase in a certain area, and the zero is taken from a special neutral bus. But if the space in the switchboard allows, you can put a two-pole circuit breaker for the phase and the neutral. In this case they will break together. Three-pole and four-pole circuit breakers are used for 380 V mains.
Two-, three- and four-pole circuit breakers are also used as lead-in circuit breaker.
The other technical characteristics are operational and are selected on the basis of the parameters of the network, the consumers' power and the characteristics of the cable.
Circuit breaker rating selection according to load capacity
When selecting the circuit breaker rating, it is necessary to correctly calculate the maximum load of the electrical section of the network.
A table showing the ratio of cable cross-section to circuit breaker rating to the power consumption is shown below:
| Cross section of copper conductors | Current carrying capacity | Mains power 220 V | Rated current | Current limit |
|---|---|---|---|---|
| 1.5 mm² | 19 А | 4.1 kW | 10 А | 16 А |
| 2.5 mm² | 27 А | 5,9 kW | 16 А | 25 А |
| 4.0 mm² | 38 А | 8,3 kW | 25 А | 32 А |
| 6.0 mm² | 46 А | 10,1 kW | 32 А | 40 А |
| 10.0 mm² | 70 А | 15,4 kW | 50 А | 63 А |
For example, for sockets in an apartment, the most common copper wire used is 2.5 mm². According to the table above, such a wire can withstand a current up to 27 A, but the circuit breaker is selected for 16 A. Similarly, a copper cable 1.5 mm² and a circuit breaker rating of 10 A are used for lighting.
Breaking capacity
The breaking capacity of a circuit breaker is the ability of the circuit breaker to trip at extremely high short-circuit currents. This characteristic is indicated on the circuit breaker in amperes: 4500 A, 6000 A, 10000 A. That is, when the instantaneous short-circuit current is high, but does not reach 4500 amperes, the automatic device is able to work and open the electric circuit.
In apartments, you can most often find circuit breakers with a breaking capacity of 4500 A or 6000 A.
Time-current characteristics
If the current flowing through the circuit breaker exceeds the rated value, the circuit breaker should logically trip. So it will happen, but with some delay. The time it takes for the circuit breaker to trip depends on the magnitude and duration of this overcurrent. The greater the difference, the faster the circuit breaker will trip.
In the documentation of the circuit breaker you can see a special graph of the value of the ratio of the current to the rated current, depending on the time when it happens. The lower the current, the longer the time.
In front of the circuit breaker rating is a Latin letter, which corresponds to the maximum current value. The most common values are:
- В - 3 to 5 times the rated current value;
- С - 5-10 times the nominal current (This is the most common type installed in apartments.);
- D - 10-20 times (are used for equipment with high inrush current).
What manufacturers should be trusted
The choice of automatic unit is made taking into account the firm-manufacturer. Popular and quality brands include: ABB, Schneider Electric, Legrand and some others. Affordable products with low prices produce firms EKF, IEK, TDM and others. In operation, many products behave almost identically, so you should not always pay extra money for a brand for the same quality of products. Schneider Electric products can cost 3-5 times more than IEK.
TDM - The product is manufactured in China in two series: VA 47-29 and VA 47-63. VA 47-29 has notches on the body for passive cooling. You can seal the device with special plugs, sold separately. VA 47-63 is available without cooling notches. Price of all products is within 130 rubles.
Chinese company "Energy". produces the same series as TDM, but with side recesses and a power indicator. Series 47-63 without indicator and recesses on the body.
Products IEK (China) have gained popularity among customers, as well as products of DEKraft и EKF.
KEAZ - Kursk plant, which produces products of BM63 and VA 47-29 series. The switch set includes seals, there is an indication of the on state.
Hungarian products GE have a noticeable weight and are very popular.
Moeller are made in Serbia and in Austria, they are analogues of Chinese circuit breakers, but have higher quality of assembling.
Schneider Electric manufactures several series of products. The cost is within 150-180 rubles. The alternative products are the company's Legrand TX..
In Russia, many electricians like the company's products ABB (Germany), which is of high quality and reliability. Two series are produced: S (industrial series) and SH (consumer series). The price of the products is 250-300 rubles.
A circuit breaker is required in the electrical circuit of any network. For proper selection you need to calculate the total load and get the current limit. Check with the table and make sure that the wire cross-section and the rating of the circuit breaker match each other. A properly selected circuit breaker eliminates the possibility of a fire due to melted wires or a short circuit in the network.
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