When designing an electrical network at an enterprise or in an apartment, one cannot do without the installation of circuit breakers. They protect the property of consumers and human lives from unforeseen situations. A professional electrician should know well how to choose the right circuit breakers for reliable and safe operation of the electrical network, how to select machines according to the power of the load used and other parameters.
Content
What is a circuit breaker used for?
A circuit breaker or simply a machine is necessary to prevent overheating of the wire insulation and protect the electrical circuit from a short circuit current. In addition, if there is an automatic switch, the maintenance of electrical lines becomes more convenient, since at any time you can de-energize the circuit in the required area.
To perform these tasks, the machine has a thermal and electromagnetic release in its design. Each circuit breaker is designed for a specific rated current and time-current characteristic. The maximum operating current of the line depends on these parameters.
When passing through the wires of electric current, the wire heats up and the stronger, the larger its value. If an automaton is not installed in the circuit, then at a certain current value, the insulation may begin to melt, which can lead to a fire.
What are automatic protection
Circuit breakers for the apartment are modular devices. This means that they can be installed in residential switchboards on a special DIN rail, while their overall dimensions are the same for different manufacturers and the same number of poles.
Non-modular circuit breakers are also found in electrical cabinets in an enterprise or transformer substations. They differ in large overall dimensions and rated current. They look like the picture below.
According to the number of poles, the machines are divided into single-pole, two-pole, three-pole and four-pole. Most often, a single-phase electrical network is designed in such a way that a single-pole machine breaks the phase in a certain area, and zero is taken from a special zero bus. But if the place in the shield allows, you can also put a two-pole machine to zero and phase on the network section. At the same time, they will be torn together. Three-pole and four-pole circuit breakers are used for a 380 V network.
Also two, rubs and four-pole machines are used as introductory.
The remaining technical characteristics are related to the working ones and are selected based on the parameters of the network, the power of consumers and the characteristics of the cable.
The choice of the nominal value of the machine according to the load power
When choosing the rating of the circuit breaker, it is necessary to correctly calculate the maximum load of the electrical section of the network.
The table of the ratio of the cable section and the rating of the circuit breaker to the power consumption is given below:
| Cross section of copper conductors | Permissible load current | Mains power 220 V | Rated current | Limit current |
|---|---|---|---|---|
| 1.5 mm² | 19 A | 4.1 kW | 10 A | 16 A |
| 2.5 mm² | 27 A | 5.9 kW | 16 A | 25 A |
| 4.0 mm² | 38 A | 8.3 kW | 25 A | 32 A |
| 6.0 mm² | 46 A | 10.1 kW | 32 A | 40 A |
| 10.0 mm² | 70 A | 15.4 kW | 50 A | 63 A |
For example, for sockets in an apartment, a copper wire cross section of 2.5 mm² is most often used. According to the table above, such a wire can withstand currents up to 27 A, but the machine is selected for 16 A. Similarly, a 1.5 mm² copper cable and a circuit breaker rating of 10 A are used for lighting.
Breaking capacity
The breaking capacity of the circuit breaker is the ability of the circuit breaker to turn off at extremely high short-circuit currents. On the machine, this characteristic is indicated in amperes: 4500 A, 6000 A, 10000 A. That is, with a large instantaneous short-circuit current, but not reaching 4500 amperes, the machine is able to work out and open the electrical circuit.
In apartments, you can most often find machines with a breaking capacity of 4500 A or 6000 A.
Time-current characteristic
If the current passing through the circuit breaker exceeds the nominal value, logically, the machine must work.So it will happen, but with some delay. The time after which the machine turns off depends on the magnitude and duration of this excess of the rated current. The greater the difference, the faster the machine turns off.
In the documentation for the circuit breaker, you can see a special graph of the dependence of the ratio of the current to the rated current on the time when this happens. The lower the current, the longer the time.
Before the nominal value of the machine, a Latin letter is indicated, which is responsible for the maximum current value. The most common values are:
- AT - excess of the rated current value by 3-5 times;
- FROM - exceeding 5-10 times (most often in apartments this type is installed);
- D - 10-20 times (used for equipment with high starting current).
Which Manufacturers Should You Trust?
The choice of the machine is made taking into account the manufacturer. Popular and quality brands include: ABB, Schneider Electric, Legrand and some others. Affordable products with budget prices are produced by firms EKF, IEK, TDM and others. In operation, many products behave almost the same, so it is not always necessary to pay extra money for a brand with the same product quality. Schneider Electric products can cost 3-5 times more than IEK.
TDM - the product is produced in China in two series: BA 47-29 and BA 47-63. BA 47-29 has notches on the case for passive cooling. You can seal the device with special plugs sold separately. BA 47-63 are produced without cooling notches. The price of all products is within 130 rubles.
Chinese firm "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) has gained great popularity among buyers, as well as products of firms DEKraft and EKF.
KEAZ - a plant in Kursk, which produces products of the BM63 and VA 47-29 series. The set of switches includes seals, there is an indication of the on state.
Hungarian products G.E. have significant weight and great popularity.
Moeller produced in Serbia and Austria, they are analogues of Chinese automatic protection devices, but have a higher build quality.
Schneider Electric produces several series of products. The cost is within 150-180 rubles. An alternative is the company's products Legrand TX.
In Russia, many electricians love the company's products ABB (Germany), which is of high quality and reliability. Two series are produced: S (industrial series) and SH (household series). Products cost 250-300 rubles.
A circuit breaker is necessary in the electrical circuit of any network. For the right choice, you need to calculate the total load and get the current limit. Check the table and make sure that the cross section of the wire and the rating of the machine correspond to 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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