Selection of the circuit breaker: the types and characteristics of the machines

I'm sure many of us have wondered why the circuit breakers so quickly pushed out of outdated electrical circuit fuses? Activity justified their introduction some very convincing arguments, including the ability to buy this kind of protection, perfectly appropriate time, current data of specific types of electrical equipment.

Not sure what kind of machine you need and do not know how to choose it? We will help you find the right solution - in the article the classification of these devices. As well as important characteristics, which should pay attention to when selecting the circuit breaker.

To make it easier to deal with guns, supplemented with visual material of the paper photos and useful videorekomendatsiyami from experts.

The content of the article:

  • Classification breakers
    • According to the rated breaking capacity
    • According to the number of poles
    • According to the time-current characteristic
    • The nominal operating current
  • Selection and sizing of circuit breakers
    • Step # 1 - Define automatic power
    • Step # 2 - Calculation of the nominal power machine
    • Step # 3 - Calculation of the rated current
    • Step # 4 - Definition of time-current characteristics
  • Conclusions and useful videos on the topic

Classification breakers

Automatic almost instantly disables it entrusted line, eliminating the wiring damage and the feeding equipment from the network. Once executed off a branch, you can immediately start again, do not change the safety device.

Usually circuit breakers chosen for the four key parameters - rated breaking capacity, the number of poles, the time-current characteristics, the rated operating current.

According to the rated breaking capacity

This characteristic indicates a permissible short-circuit current (CC), wherein the triggered switch and by opening the circuit and de-energize the wiring devices connected thereto.

By this parameter share three kinds machines - 4.5 kA 6 kA and 10 kA.

  1. Machines to 4.5 kA (4500 A) It is commonly used to avoid damage to the power lines of private residential properties. wiring resistance from the substation to the point of fault is approximately 0.05 ohms, which allows the limiting current of about 500 A.
  2. Devices for 6 kA (6000 A) used for short-circuit protection residential areas, public places, where the line resistance of 0.04 Ohm can reach, which increases the likelihood of getting closure to 5.5 kA.
  3. Switches 10 kA (10000 A) are used to protect electrical installations for industrial use. Current up to 10,000 A can occur in short electrical circuit, located close to the substation.

Before selecting switch optimal modification is important to understand whether the short-circuit currents may be in excess of 4.5 kA or 6 kA?

Marking breaker

Rated breaking capacity indicated in the documentation for the switch and on the body as a cipher - 4500A, 600A, 10000A or 4,5kA, 6kA, 10kA. The front part of the device contains information about the manufacturer, model, rated voltage, consisting of data time-current characteristic, the operating current

Turning off the machine fault occurs at predetermined values. Most often used modification A. 6000 switches for household use

Model 4500 A are not used for the protection of modern power grids, and in some countries they are not allowed to operate.

If you are interested in how to correctly convert Amps to Watts, be sure to check with the material set out the following article.

How to correctly select the circuit breaker

When automatic registration disconnection fault generates electromagnetic coil (situation A). When exceeding the rated current network opens bimetallic plate (situation B)

breaker's job is to protect the wiring (not hardware and users) and short-circuit by melting the insulation during the passage of currents above the nominal values.

According to the number of poles

This characteristic indicates the maximum possible number of wires that can be connected to the AV network protection.

Their cut-out in case of emergency (in excess of the permissible values ​​or current level exceeding the current-time curve).

This characteristic indicates the maximum possible number of wires that can be connected to the AV network protection. Their cut-out in case of emergency (in excess of the permissible values ​​or current level exceeding the current-time curve).

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The specificity of single-pole machines

The single-pole circuit breakers are set to the input of each individual line of single-phase network

Place setting of a bipolar machine

Two-pole machines have shields in single-phase networks to shut off the power to all lines

Using the three-pole machines

The three-pole tripping the automatic devices are used to break a three-phase line

Installing cheterehpolyusnogo machine

Four-pole circuit breaker disconnects the three-phase line and zero work

The specificity of single-pole machines

The specificity of single-pole machines

Place setting of a bipolar machine

Place setting of a bipolar machine

Using the three-pole machines

Using the three-pole machines

Installing cheterehpolyusnogo machine

Installing cheterehpolyusnogo machine

Features single-pole machines

Switch unipolar type is the simplest modification of the machine. It is designed to protect the individual chains, as well as single-phase, two-phase, three-phase wiring. By the design of the switch is possible to connect 2 wires - and the power cord off.

In this class of device function is to protect the wires from a fire. Neutral wiring itself is placed on the zero bus, thereby circumventing machine and the ground wire is connected to the ground bus separately.

Single-pole switch

Connecting a single-pole AB produced single wire, but sometimes use two-wire cable. Connect the power supply from the top machine, a protected line - from the bottom, which simplifies installation. Installation takes place on 18 milimetruvuyu din-rail mounting

Single-pole automatic function does not perform the opening, as when it is forced outages there is a rupture phase line and neutral is connected to a voltage source that gives a 100% guarantee protection.

Characteristics bipolar switches

When to be completely disconnected from the network wiring voltage is applied bipolar machine.

It is used as an input when, during a short-circuit or failure of the network all wiring is de-energized at the same time. This allows for timely repair works, modernization of the chain is absolutely safe.

Apply double-pole machines in the cases, if you need a separate switch for single-phase electrical appliances such as water heater, boiler, machine.

two-pole machine

Connecting bipolar machine occurs with the electrical protection circuit using 1- or 2-core wire (number of wires depends on rasklyucheniya circuit). Mounting on the rail-mounted 36 mm

Connect the machine to the protected device using a 4-wire, two of which are power wires (one directly connects to the network, and delivers the second power bridge) and two - outgoing wires that require protection, and they can be 1-, 2-, 3-wire.

Tripolar modification of circuit breakers

To protect the 3- or 4-phase-wired networks use three-pole machines. They are suitable for the connection of the star type (middle wire is left without protection, and the phase is connected to the poles) or a triangle (with the absence of a central wire).

In an accident on one of the lines itself off the other two.

The three-pole machine

Connecting tripolar AB produced 1-, 2-, 3- core wire. To install the required din-rail 54 mm

Three-pole circuit breaker serves as an input and common to all types of three-phase loads. Often the modification used in the industry for providing electric current.

The model is connected to wire 6, three of them are the phase conductors of three-phase mains. The remaining 3 are protectable. They represent the three single-phase or three-phase single wiring.

The use of four-phase machine

To protect the three-, four-phase power supply, for example, a powerful engine that is connected on the principle of the star, using four-phase machine. It is used as a main switch in the three phase four wire network.

How to choose a four-pole circuit breaker

Connecting the four-pole circuit breaker is made of 1-, 2-, 3-, 4-wire cable, the circuit depends on the type of connection, the housing mounted on din-rail 73 mm

To the body of the automaton is possible to connect eight wires, four of which are phase conductors power (of which one neutral), and presents four radiating conductors (phase 3 and 1 neutral).

According to the time-current characteristic

AB can have the same index rated load capacityBut the characteristics of the electric power consumption of devices may be different.

Power consumption can flow unevenly, vary depending on the type and load, and when switched on, switched off or continuous operation of a device.

power consumption fluctuations can be quite significant, and the range of their changes - wide. This leads to the machine is switched off due to the excess of the rated current that is false disabling network.

To eliminate the possibility that inappropriate fuse to blow when the standard is not accidental changes (Increasing amperage power change) are used with machines certain time-current characteristics (BTX).

This allows you to operate the switches with the same parameters of the currents with arbitrary admissible loads without nuisance tripping.

BTX show how long the switch will work and what ratios of current and continuous current machine at the same time will be.

Especially machines with characteristic B

Machine with said characteristics is switched off during 5-20 seconds. current figure is 3-5 with the rated machine current. These modifications are used to protect circuits that fuel standard household appliances.

Most often, the model is used to protect the wiring of apartments, private houses.

Feature C - principles of operation

Automatic Nomenclature with C 1-10 deactivated during 5-10 seconds at nominal currents.

Using switches of this group in all areas - in the home, building, industry, but they are most in demand area of ​​electrical protection apartments, houses, residential buildings.

Operation switches with characteristic D

D-class machines are used in industry and presented three-pole and four-modifications. They are used to protect a variety of powerful motors and 3-phase devices.

Response time AB - 1-10 seconds at a current of 10-14 fold that allows to apply efficiently for the protection of various transactions.

Schedule time-current characteristics

In the lower part of the graph shows the multiplicity of the nominal current values ​​on the vertical line - time off. In order to characterize the disconnection occurs at 3-5 fold excess current above the nominal current, for C - 5-10 fold for D - 10-14 fold

Powerful industrial engines work exclusively with the characteristic of AB D.

You may also be interested in viewing marking breakers in our other article.

The nominal operating current

In total there are 12 automatic versions, which differ in indicator nominal operating current - 1A, 2A, 3A, 6A, 10A, 16A, 20A, 25A, 32A, 40A. This parameter is responsible for the machine operating speed in excess of the current over the current rating.

The choice of machine power

Table illustrates each machine power limit modification, based on the connection method and the network voltage. Maximum output switch occurs when connecting the delta load

Selection circuit breaker according to the characteristic of said produce with the power wiring allowable current that can withstand the wiring in the normal mode. If the current value is unknown, it is determined by the formula, using data wire section, its material and method for laying.

Machines 1A, 2A, 3A are used to protect circuits with small currents. They are suitable to provide electricity for a small number of devices, such as a lamp or chandelier, low power cooler and other devices, which will not exceed the total power capabilities machine.

3A the switch is operated effectively in the industry, if the exercise of its three-phase delta connection type.

Breakers 6A, 10A, 16A is allowed to use to provide electricity to the individual circuits, small rooms or flats.

These models are used in the industry, with their help power the electric motors, solenoids, heaters, welding machines, connected by a separate line.

Three-, four-pole machines 16A are used as input with a three-phase power circuit. In the production of gears with preference for D-curve.

Machines 20A, 25A, 32A are used to protect the wiring of modern apartments, they are able to provide electricity for washing machines, heaters, Electric driers and other appliances with high power. 25A model is used as an input machine.

Switches 40A, 50A, 63A are a class of high-power devices. They are used to provide electricity to power heavy-duty equipment in households, industry, civil construction.

Selection and sizing of circuit breakers

Knowing the characteristics of AV, you can determine which machine is suitable for a particular purpose. But before choosing the optimal model is necessary to make some calculations, with which you can accurately determine the parameters of the desired device.

Step # 1 - Define automatic power

When choosing a machine it is important to consider the total power of the connected devices.

For example, it is necessary to connect the machine to the power supply of kitchen appliances. Assume outlet will be connected to the coffee machine (1000 W), a cooler (500 W), oven (2000 W), the microwave oven (2000 W), electric (1000 W). The total capacity is equal to 1000 + 500 + 2000 + 2000 + 1000 = 6500 (W) or 6.5 kV.

Table power devices

The table below shows the nominal power of some household appliances necessary for their work. According to the normative data selected cross-section of the power line for their food and the machine to protect the wiring

If you look at the table on the machine to connect the power to take into account that the standard voltage wiring in the home conditions is 220, the operation is suitable for single-pole or two-pole machine 32A with a total capacity of 7 kW.

Keep in mind that you may need a lot of power consumption, as in the operation may need to connect any other appliances that were not originally included. To provide for this situation, in the calculation of the total consumption is used up factor.

Assume, by adding an additional electrical power increase required 1.5 kW. Then you must take a factor of 1.5 and multiply it by obtaining estimated power.

In the calculations, it sometimes makes sense to use a step-down ratio. It is used when the simultaneous use of multiple devices is possible.

Suppose the total capacity of the wiring for kitchen was 3.1 kW. Then, the reduction factor is 1, since considered the minimum number of devices connected simultaneously.

If one of the devices can not be connected with the other, the reduction factor taking less than one.

Step # 2 - Calculation of the nominal power machine

Rated power - it is the power at which the wiring disconnection occurs.

It is calculated as follows:

M = N * CT * cos (φ),


  • M - power (W);
  • N - the power supply voltage (V);
  • CT - current strength, able to pass through the machine (Amp);
  • cos (φ) - the value of the cosine of the angle of receiving the angle shift between the phases and voltages.

Cosine value is generally equal to 1, since the phase shift between current and voltage is almost not.

The formula expressing CT:

CT = M / N,

The power we have already determined, and the supply voltage is usually 220V.

If the total power is 3.1 kW, then:

CT = 3100/220 = 14.

The resulting current will be 14 A.

To calculate the three-phase load when using the same formula, but take into account angular shifts, which can reach high values. Usually on the equipment to be connected, they are indicated.

Step # 3 - Calculation of the rated current

Calculate the rated current is possible by documentation of wiring, but if it does not, it is determined based on the characteristics of the conductor.

For the calculation you need the following data:

  • area section of the conductor;
  • used for wire material (copper or aluminum);
  • method of laying.

In a domestic environment it is usually located in a wall wiring.

Measurement section of the wire with a micrometer

To calculate the cross-sectional area need a micrometer or caliper. It should be measured solely conductive wire, not the wire and insulation

After making the necessary measurements, we calculate the cross-sectional area:

S = 0,785 * D * D,


  • D - a conductor diameter (mm);
  • S - conductor cross-sectional area (mm2).

Next, we use the table below.

Table AC power conductor and

Determining the material from which the conductor wires were formed, and calculating the cross-sectional area, one can determine parameters of current and power that can withstand the electrical wiring. Data referred to the wiring hidden in the wall

In view of the data select operating current of the machine and its denomination. It should be equal to or smaller than the operating current. In some cases, allowed to use the machine with a nominal value greater than the current wiring current.

Step # 4 - Definition of time-current characteristics

To correctly determine BTX, it is necessary to consider the starting currents of connected loads.

The desired data can be found by using the table below.

Table time-current characteristics of the devices

Table I shows some types of electrical devices, as well as the multiplicity of starting current and pulse width in seconds

According to the table can be determined current strength (in amps) when the device is turned on, and the period over which the limiting current will occur again.

For example, if we take an electric grinder, the thickness of which is 1.5 kW, calculated for it the operating current of the tables (this will be 6.81 A) and, given the multiplicity of starting current (up to 7 fold) we obtain the value current 6.81 * 7 = 48 (A).

This current strength occurs at intervals of 1-3 seconds. Considering the graphics VTK class B, one can see that the overload circuit breaker will trip in the first seconds after starting grinder.

Obviously, the multiplicity of this unit corresponds to the class, so with an automatic characteristic C must use to operate the electric mincer.

For domestic use usually use switches that meet the characteristics B and C. In industry for equipment with multiple large currents (motors, power and other units.) Produces a current of up to 10 times, so it is advisable to use D-modifying device.

However, one should take into account the capacity of such devices, as well as the duration of the inrush current.

Autonomous automated switches differ from conventional in that they are placed in individual switchboards.

The device includes circuit protection function of the unexpected surges, power outage at all or a network area.

Conclusions and useful videos on the topic

Selecting AB for current characteristics and an example of the current calculation are discussed in the following video:

rated current calculation AB shown in the following video:

Machines are mounted on the house or apartment entrance. They are located in durable plastic boxes. AB in the presence of the house electric circuit - security deposit. Devices allow timely disconnecting the power lines if the network parameters exceed a predetermined threshold.

Taking into account the main characteristics of circuit breakers, as well as having made the correct calculations, you can make the right choice of the equipment and its installation.

If you have knowledge or experience performing electrical work, please share it with our readers. Leave your comments on the choice of the circuit breaker and the nuances of installing it in the comments below.

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