Choosing a circuit breaker: types and characteristics of automatic machines
Surely many of us wondered why the circuit breakers so quickly replaced outdated fuses from the electrical circuits? The activity of their implementation is justified by a number of very convincing arguments, among which the opportunity to buy this type of protection, which ideally matches the time-current data of specific types of electrical equipment.
Doubt what kind of machine you need and don’t know how to choose it right? We will help you find the right solution - the article discusses the classification of these devices. As well as important characteristics that you should pay close attention to when choosing a circuit breaker.
To make it easier for you to deal with machines, the article material is supplemented by visual photos and useful video recommendations from experts.
The content of the article:
- Classification of circuit breakers
- Selection and calculation of circuit breakers
- Conclusions and useful video on the topic
Classification of circuit breakers
The machine almost instantly disconnects the line entrusted to it, which eliminates damage to the wiring and network-powered equipment. After a shutdown has been completed, the branch can be immediately restarted without having to replace the safety device.
Usually circuit breakers they are selected according to four key parameters - rated breaking capacity, number of poles, time-current characteristic, rated operating current.
Rated breaking capacity
This characteristic indicates the permissible short circuit current (short circuit) at which the circuit breaker will trip and, by opening the circuit, will disconnect the wiring and devices connected to it.
According to this parameter, three types of machines are divided - 4.5 kA, 6 kA, 10 kA.
- 4.5 kA automatic machines (4500 A) usually used to prevent damage to power lines of private residential facilities. The resistance of the wiring from the substation to the fault location is approximately 0.05 Ohms, which gives a current limit of about 500 A.
- 6 kA (6000 A) devices they are used to protect against short-circuiting of the residential sector, public places where the line resistance can reach 0.04 Ohm, which increases the likelihood of getting a short circuit to 5.5 kA.
- 10 kA circuit breakers (10,000 A) used to protect electrical installations for industrial use. A current of up to 10,000 A can occur in a short circuit located close to the substation.
Before choosing the optimal circuit breaker modification, it is important to understand whether short-circuit currents exceeding 4.5 kA or 6 kA are possible?
Turning off the machine occurs when the set values are shorted. Most often for domestic use, circuit breakers of 6000 A modification are used.
The 4500 A models are practically not used to protect modern electric networks, and in some countries they are forbidden to operate.
If you are interested in how to correctly transfer Amperes to Watts, we recommend that you familiarize yourself with the material set forth in the next article.
The operation of the circuit breaker is to protect the wiring (and not the equipment and users) from the short circuit and from the melting of the insulation when currents pass above the nominal values.
By the number of poles
This characteristic indicates the maximum possible number of wires that can be connected to the AV to protect the network.
Their shutdown occurs when an emergency occurs (during exceeding the permissible current indicators or exceeding the level of the time-current curve).
This characteristic indicates the maximum possible number of wires that can be connected to the AV to protect the network. Their shutdown occurs when an emergency occurs (during exceeding the permissible current indicators or exceeding the level of the time-current curve).
Single pole circuit breakers
A single-pole type switch is the simplest modification of the machine. It is designed to protect individual circuits, as well as single-phase, two-phase, three-phase wiring. It is possible to connect 2 wires to the circuit breaker design - a power wire and an outgoing one.
The functions of this class of device include only the protection of the wire from fire. The neutral wiring itself is placed on the zero bus, thereby bypassing the machine, and the ground wire is connected separately to the ground bus.
A single-pole circuit breaker does not perform the function of an input, since when it is forced to turn off, the phase line breaks and the neutral is connected to a voltage source, which does not give a 100% guarantee of protection.
Bipolar Circuit Breakers
When it is necessary to completely disconnect the wiring network from voltage, a two-pole automatic device is used.
It is used as an introduction, when during a short circuit or a network failure, all electrical wiring is de-energized at the same time. This allows you to carry out timely repair work, chain modernization is absolutely safe.
Bipolar machines are used in cases where a separate switch is needed for a single-phase electrical appliance, for example, a water heater, boiler, machine.
The machine is connected to the protected device using 4 wires, two of which are power wires (one of them is directly connected to the network, and the second supplies power with a jumper) and two are outgoing wires that require protection, and they can be 1-, 2- 3 wire.
Three Pole Circuit Breakers
To protect a three-phase 3- or 4-wire network, three-pole machines are used. They are suitable for connection by the type of a star (the middle wire is left unprotected, and the phase wires are connected to the poles) or a triangle (with a missing central wire).
In the event of an accident on one of the lines, the other two are disconnected on their own.
A three-pole switch serves as an input and common for all types of three-phase loads. Often, modifications are used in industry to provide electric motors with current.
Up to 6 wires are connected to the model, 3 of them are represented by phase wires of a three-phase power supply network. The remaining 3 are protected. They represent three single-phase or one three-phase wiring.
Four Pole Circuit Breakers
To protect a three-, four-phase mains, for example, a powerful motor connected according to the principle of “stars with a zero point removed”, a four-pole circuit breaker is used. It is used as an input switch to a three-phase four-wire network.
It is possible to connect eight wires to the machine case, of which three are phase wires of the power supply network (+ from one zero) and four are represented by outgoing wires (3 phase + 1 neutral).
Single-phase consumers are powered by a voltage of 220 V, which can be obtained by taking one of the phases and the neutral conductor (neutral) of the electrical network. That is, in this case, in addition to the three phases of the electric network, there is another conductor - zero, therefore, for the protection and switching of such an electric network, four-pole circuit breakers are installed that break all four conductors.
By time-current characteristic
AB can have the same rate rated load power, but the characteristics of electricity consumption by devices may be different.
Power consumption can flow unevenly, depending on the type and load, as well as when you turn on, turn off or constant operation of a device.
Fluctuations in power consumption can be quite significant, and the range of their changes is wide. This leads to the shutdown of the machine due to exceeding the rated current, which is considered a false disconnection of the network.
In order to exclude the possibility of inappropriate fuse tripping during non-emergency standard changes (increase in current strength, power change), machines with certain time-current characteristics (VTX) are used.
This allows the operation of circuit breakers with the same current parameters with arbitrary permissible loads without false trips.
The BTX show how long the circuit breaker will trip and what indicators of the ratio of the current strength and the direct current of the machine will be.
Features of machines with characteristic B
The machine with the specified characteristic turns off in 5-20 seconds. The current indicator is 3-5 rated currents of the machine. These modifications are used to protect the circuits supplying household standard appliances.
Most often, the model is used to protect the wiring of apartments, private houses.
Feature C - Operation Principles
The machine with the nomenclature designation C is switched off in 1-10 seconds at 5-10 rated currents.
Circuit breakers of this group are used in all areas - in everyday life, construction, industry, but they are most in demand in the field of electrical protection of apartments, houses, residential premises.
Operation of circuit breakers with characteristic D
D-class machines are used in industry and are represented by three-pole and four-pole modifications. They are used to protect powerful electric motors and various 3-phase devices.
The response time AB is 1-10 seconds at a current multiple of 10-14, which allows it to be effectively used to protect various wiring.
Powerful industrial engines work exclusively with AB with characteristic D.
You may also be interested in readingmarking circuit breakers in our other article.
Rated operating current
In total there are 12 modifications of machines, differing in rated operating current - 1A, 2A, 3A, 6A, 10A, 16A, 20A, 25A, 32A, 40A. The parameter is responsible for the speed of operation of the machine when the current rises above the nominal value.
The choice of the switch according to the specified characteristic is made taking into account the power of the wiring, the permissible current that the wiring can withstand in normal mode. If the current value is unknown, it is determined using formulas using data on the cross section of the wire, its material and method of laying.
Automatic machines 1A, 2A, 3A are used to protect circuits with low currents. They are suitable for providing electricity to a small number of devices, for example, lamps or chandeliers, low-power refrigerators and other devices whose total power does not exceed the capabilities of the machine.
Switch 3A is effectively used in industry if it is tri-phase connected in the form of a triangle.
Switches 6A, 10A, 16A can be used to provide electricity to individual circuits, small rooms or apartments.
These models are used in industry, with their help they supply electric motors, solenoids, heaters, welding machines connected by a separate line.
Three-, four-pole circuit breakers 16A are used as input devices for a three-phase power supply circuit. In production, devices with a D-curve are preferred.
Automatic machines 20A, 25A, 32A are used to protect the wiring of modern apartments, they are able to provide washing machines, heaters, electric dryers and other equipment with high power with electricity. Model 25A is used as an introductory machine.
Switches 40A, 50A, 63A belong to the class of devices with high power.They are used to provide electricity to large-capacity power equipment in the home, industry, and civil engineering.
Selection and calculation of circuit breakers
Knowing the characteristics of AB, you can determine which machine is suitable for a particular purpose. But before choosing the optimal model, it is necessary to make some calculations with which you can accurately determine the parameters of the desired device.
Step # 1 - determining the power of the machine
When choosing a machine, it is important to consider the total power of the connected devices.
For example, you need an automatic machine to connect kitchen appliances to the power supply. Let's say a coffee maker (1000 W), a refrigerator (500 W), an oven (2000 W), a microwave oven (2000 W), an electric kettle (1000 W) will be connected to the outlet. The total power will be equal to 1000 + 500 + 2000 + 2000 + 1000 = 6500 (W) or 6.5 kV.
If you look at the table of automatic devices according to the connection power, take into account that the standard wiring voltage under domestic conditions is 220 V, then a single-pole or two-pole 32A circuit breaker with a total power of 7 kW is suitable for operation.
It should be noted that a large power consumption may be required, since during operation it may be necessary to connect other electrical appliances that were not initially taken into account. In order to foresee this situation, in the calculations of total consumption, a raising factor is used.
Suppose, by adding additional electrical equipment, an increase in power of 1.5 kW was required. Then you need to take the coefficient 1.5 and multiply it by the calculated design power.
In calculations it is sometimes advisable to use a reduction factor. It is used when the simultaneous use of several devices is impossible.
Suppose the total wiring power for the kitchen was 3.1 kW. Then the reduction factor is 1, since the minimum number of devices connected at the same time is taken into account.
If one of the devices cannot be connected with the others, then the reduction factor is taken less than unity.
Step # 2 - calculation of the rated power of the machine
The rated power is the power at which the wiring is not disconnected.
It is calculated by the formula:
M = N * CT * cos (φ),
- M - power (watts);
- N - mains voltage (Volt);
- ST - amperage that can pass through the machine (Ampere);
- cos (φ) - the cosine of the angle, taking the value of the angle of shift between phases and voltage.
The cosine value is usually equal to 1, since there is practically no shift between the phases of the current and voltage.
From the formula we express CT:
CT = M / N,
We have already determined the power, and the mains voltage is usually 220 volts.
If the total power is 3.1 kW, then:
CT = 3100/220 = 14.
The resulting current will be 14 A.
For the calculation at a three-phase load, the same formula is used, but angular shifts that can reach large values are taken into account. Usually they are indicated on the connected equipment.
Step # 3 - calculation of rated current
The rated current can be calculated according to the documentation for the wiring, but if it is not there, then it is determined based on the characteristics of the conductor.
For calculations, the following data is required:
- area conductor cross-sections;
- material used for cores (copper or aluminum);
- laying method.
In domestic conditions, wiring is usually located in the wall.
Having made the necessary measurements, we calculate the cross-sectional area:
S = 0.785 * D * D,
- D Is the diameter of the conductor (mm);
- S - conductor cross-sectional area (mm2).
Next, use the table below.
Based on the data obtained, we select the operating current of the machine, as well as its nominal value. It should be equal to or less than the operating current. In some cases, it is allowed to use machines with a rating that exceeds the current wiring current.
Step # 4 - determining the current-time characteristic
To correctly determine the VTX, it is necessary to take into account the starting currents of the connected loads.
The necessary data can be found using the table below.
According to the table, you can determine the current strength (in Amperes) when the device is turned on, as well as the period through which the limiting current will occur again.
For example, if we take an electric meat grinder, the power of which is 1.5 kW, calculate the working current for it from the tables (this will be 6.81 A) and, given the multiplicity of the starting current (up to 7 times), we get the current value 6.81 * 7 = 48 (A).
A current of this force flows with a frequency of 1-3 seconds. Given the VTK schedules for class B, you can see that when overloaded, the circuit breaker will trip in the first seconds after starting the meat grinder.
Obviously, the multiplicity of this device corresponds to class C, therefore, an automatic machine with characteristic C must be used to ensure the operation of an electric meat grinder.
For domestic needs, switches that meet the characteristics of B and C are usually used. In industry, equipment with large multiple currents (motors, power supplies, etc.) generates current up to 10 times, so it is advisable to use D-modifications of the device.
However, the power of such devices, as well as the duration of the starting current, should be taken into account.
Autonomous automated switches differ from ordinary ones in that they are installed in separate switchboards.
The functions of the device include protecting the circuit from unexpected voltage surges, power outages on an entire or a specific part of the network.
Conclusions and useful video on the topic
The choice of AB according to the current characteristic and an example of calculating the current are considered in the following video:
The calculation of the rated current AB is demonstrated in the following video:
Automatic machines are mounted at the entrance of a house or apartment. They are located in durable plastic boxes. The presence of AB in the home electrical circuit is a guarantee of security. Devices allow timely disconnecting the power line if the network parameters exceed a predetermined threshold.
Given the basic characteristics of circuit breakers, as well as making correct calculations, you can make the right choice of this device and its installation.
If you have knowledge or experience in performing electrical work, please share it with our readers. Leave your comments about the choice of the circuit breaker and the nuances of its installation in the comments below.