The response time is less than y. Marking of circuit breakers. Types, characteristics and purpose of circuit breakers

It is paradoxical, but the fact - after the electronic devices were no longer using "fuses", which burned in any abnormal changes in the network parameters, the number of "burned" electrical appliances has increased significantly, despite the fact that "safety devices" are much more sensitive , react faster and are able to prevent even a short circuit.

Ask what is the catch? The answer is simple. Convenience is the operating principle of the circuit breaker, which allows it to be switched on again. Few people will risk simply replacing the fuse without understanding the cause of the failure of the device. After all, you have to look for one more if something went wrong. Therefore, when the fuse burned, the owner, first of all, tried to find the cause of "combustion", and not a spare fuse, or plugs. Automatic security systems eliminated the search for "spare parts", while allowing the owner multiple inclusions of the "knocked out machine" to finish off the non-functioning device, and even the entire electrical network. Hence such statistics. Let's find out what a circuit breaker is, "with what it's eaten," and at the same time, how to handle it correctly.

Basic principles of circuit breakers

Let's start with the electrical network, which protects the circuit breaker, the characteristics of which directly depend on the parameters of the protected section of the network. The task of the machine is to monitor the current parameters in this circuit, avoiding overloads, immediately turn off the section if there is an overheating of the wires, or short circuit, and also if the current exceeds the permissible threshold values. Thus, between the point at which your object is connected to the power system and the device that consumes energy, there are two main elements. The first is an automatic switch whose characteristics are related to the second one by a cable (wires), more precisely, with the number of wires and the cross-section of this cable. Here are 2 simple examples:

In the hallway a few light bulbs, with a total capacity of 400 watts and a section of a warm floor, with a capacity of 1500 watts. The network is 220 volts, which means (Watt = Volt x Ampere), 1400 Watts divided by 220 volts is equal to 8.4 Ampere. That is, to protect this area, it is enough to have an automatic machine with a current strength of 8.4 Ampere, and we supplied 10 A.

In the kitchen there are 10 devices with a capacity of 1200 watts, and only 12,000 watts. Therefore, for this site: 12000 divide by 220, we need 54 amperes, but we limited ourselves to a standard automatic device of 25 amperes.

To understand the principle of action automatic switches  these examples are sufficient.

In the hallway, the machine will switch off, most likely, only when there is a short circuit in the circuit. The probability of disconnection due to overload, overheating of this part of the network is negligible (with the current parameters coming from outside unchanged). There are also no special requirements for the cross-section of wires on this site.    Attention! In this hallway, given as an example, there are no outlets for connecting other devices!

But in the kitchen, the inclusion of one after another devices will lead to the following situation:
   Each connected device (+1200 watts) will increase the load, and hence the current in this circuit. The included 5th device will raise the current to: 5 * 1200/220 = 27.3 A.

The automaton "knows" that the current strength in this section can not exceed 25 amperes. Therefore, the inclusion of the 5th device will lead to the disconnection of the kitchen from the network. (To be more precise, if the characteristic of the automaton is 1 to 1, what is below).

Council. In the event of a protection circuit, consider the last action (turning on the iron, for example), turn off the appliances in the de-energized zone (preferably - by removing the plugs from the sockets), and only after making sure that everything is off, wait ten minutes (to cool the overheated fuse elements), try it enable again.

So, the machine, having detected the excess of the current parameter, de-energized the network section. What happens if there is a short circuit in the kitchen? Closing leads to a sharp increase in the load, and instantaneous increase in the amperage. In this case, the wires become heating elements, heating up to high temperatures. Heating takes place simultaneously in the entire circuit, over which the current flows. At the same time, the current can instantaneously increase to very large values. This can lead to burn-out of the contacts and to an unavoidable fire, if the tripping time of the circuit-breaker is not selected correctly.

Having thought about the above, you can easily understand the other characteristics of machines, how to "read" them, as well as the basic principles of the operation of circuit breakers, including for industrial applications.

Device, marking and technical characteristics of automatic devices

From the functions that the protective device performs, its device follows. This is a switch that allows the opening of the electrical circuit from exceeding the current, or from heating. That is, in the machine there are two circuits, aimed at guaranteed disconnection of the circuit. When heated, the bimetallic plate changes the volume, thereby ensuring the physical separation of the contacts (thermal release). The electromagnetic release, with unacceptable changes in the current parameters, creates fields inside the coil where the moving pusher is located, also the breaking circuit. The arcing that occurs when the electric arc is turned on and off at the contacts extinguishes the arc chute. There are other design features  for different types of machines, but these are basic.

Classification of automata

By the number of poles: single-pole and two-pole switches with 1 or 2 protected poles, three-pole switches  with 3 protected poles, 4-pole switches with 3 or 4 protected poles.

In its protection from external influences: closed or open execution.

By the way of its installation: wall type, recessed type, installation in distribution cabinets (including mounting on the DIN-rail), combined.

By the method of its attachment: having or not having a mechanical fastening.

According to the instantaneous tripping current, denoted by types B, C, D.

The labeling of automatic machines reflects the features of a particular device, is rigidly standardized, it can be clearly seen on the proposed photo:

The technical characteristics (reflected in the marking) correspond to the following values:

How to apply in practice the knowledge of the characteristics for the correct selection of the machine?

Any circuit-breaker, whose characteristics are approximately understandable to us, must correspond, first of all, to the main purpose of protecting the network section. At the same time, it must ensure the absence of unreasonable shutdowns on the one hand, and prevent a "breakdown of protection" inside the network, which could lead to the failure of the electrical appliance (devices).

We begin by evaluating our electricity network - the approximate length of the wires, the number and cross-section of the conductors, the presence of a ground loop, the quality of insulation, and the number of electrical appliances used (frequency and power).

The longer the cables, the greater their own resistance, but for a standard apartment, which uses veins of a cross section of 1.5 mm. the most common automatic machines of class C 220V are well suited. The number of poles will give us a shield, mounting features and features of our network. It is advisable to consult with those who will carry out the installation! The current intensity in the marking (for example, C16) is determined from the load of the included instruments, taking the threshold value as a 2-fold nominal value, in order to avoid false trips. Let's assume that the amperage at simultaneous switching on of all devices (calculation see above) will make 35 Amperes, considering that such a situation is supernumerary, it will suffice to apply the automatic machine C25. The machine will not shut down, but an additional "emergency" load increase will serve as the guarantee of a timely shutdown.

Council. Switching on the device always leads to a short-time increase in the current in the network, so the simultaneous connection of several instruments at the same time can damage the wiring and almost always lead to a power failure by the machine. Turn on the appliances in turn, especially using heat, or requiring high power!

Choose a manufacturer

Having determined the voltage, current and speed of work, which is actually limited to the price of automata of one class, we will choose the manufacturer. Despite the conventional wisdom, Russian-made circuit breakers are very reliable devices that are manufactured in strict accordance with GOSTs (which are more demanding than those of manufacturers) and are cheaper. In any case, the most correct thing is choosing all the shield equipment (not just machines, but also racks, shield and accessories) from one manufacturer, which will not only facilitate the installation (due to full compatibility), but also save time by buying everything in one place.

After the specification for the introductory site (the shield, automatic machines, etc.) is made up, it is recommended to give it for evaluation to specialists. If this task was entrusted to specialists using our recommendations, check whether the choice of characteristics is correct from your point of view. If you have any questions, do not calm yourself "they need to know" - be sure to find out why this option was suggested.

Human protection is above all!

In conclusion, let's say about one more device that should become the head protection device in your shield. In the article, we examined the aspects of protecting the network and devices, now we will talk how to protect a person. For this purpose, a so-called automatic differential current switch is used, the purpose of which, apart from tracking currents, is to monitor "leaks" and supernumerary changes in the network. Simply put, this type of automaton recognizes that unauthorized changes in characteristics occur in the network, falling into the category of "damage to insulation", "possible touch of a person to live wires", etc.

Such detection leads to instantaneous de-energizing of the network section. Sometimes automatic residual current circuit breakers are called RCDs (Device protective shutdown), MDZ (Module of differentiated protection). They can be used in combination with other automata. The main difference of this machine is that it works to protect a person from electric shock. The most relevant are devices for connecting bathrooms and baths (preferably with maximum sensitivity) and kitchens. But today, many prefer to put such switches on all sections of the network in the apartment.

We hope that this article will be useful to you when choosing an RCD and, as a consequence, your electricity network, electrical appliances will be reliably protected.

    Content:

When all the devices and itself electrical network  function in the normal mode, they observe the usual current flow. This phenomenon fully applies to the circuit breaker. However, in case of excess of the current, for whatever reason, its nominal value, the protective device operates and the circuit opens. The parameter of such operation is known as the time-current characteristic of the circuit-breaker. It is the dependence of the response time of the machine and the relationship between the actual current flowing through the machine and the nominal current of the device.

What is the time-current characteristic for?

Difficulties of practical application of this parameter are primarily associated with charts that need to be correctly read and applied in practice. Disconnection of machines with the same nominal value will not occur in the same way in the case of different current surges. Therefore, for each type of circuit breaker, there is an own curve displayed on the graph. This enables the use of circuit breakers with different characteristics for a particular type of load.

As a result, the circuit breaker performs a protective current function and simultaneously minimizes false alarms. This is the main practical meaning of the time-current characteristic.

In the field of energy, there are often situations in which an increase in current for a short time is not associated with the emergence of an emergency operating mode. In these cases, protective devices should not react to such changes. This happens when the motors are turned on, when a significant current jump is observed, several times higher than the rated value. If you follow the logical conclusions, there must be a mandatory shutdown of the machine. For example, if the device is set to 10 A and the inrush current is 12 A, this will cause the protection to function unavoidably. In order to avoid this, it is required to increase the threshold, for example, up to 16 amperes. However, in case the device may not shut down.

Too low a trigger level will cause the machine to react even to minor jumps. Solve this problem allows a time-current characteristic, which determines the main operating mode of each protective device.

Time-current characteristics of automata

The tripping of the circuit breakers is due to the action of its main elements - the thermal and electromagnetic release. The design of the thermal release consists of a bimetallic plate heated by the flowing current. As a result, it bends and activates the release mechanism. To operate, a sustained load is required, inversely proportional to the time delay. The overload level directly affects the heating of the plate and the operating time of the thermal release.

The main components of the electromagnetic release are a coil and a core. When the current reaches a certain level, the magnetic field of the coil pulls the core, under the action of which the tripping mechanism operates. The device instantly fires in case of short circuits, without waiting for the heating of the thermal release. The response time of the machine depends on the current flowing through the circuit breaker. This dependence is precisely the time characteristic of the protective device.

The Latin symbols B, C and D are printed on the body of each device. Each of them corresponds to the multiplicity of the setting of the electromagnetic release to the nominal value of the automaton. That is, with the help of these letters, the current of the instantaneous tripping of the release or the sensitivity of the circuit breaker is displayed. This parameter indicates the minimum current at which the safety device switches off instantly. Thus, Latin letters denote the time-current characteristic of each particular automaton. The symbol "B" corresponds to the characteristics of 3-5 x ln, "C" - 5-10 x ln and "D" - 10-20 x ln.

The significance of these figures should be considered in the case of two automata, equal in power, that is, with the same nominal current, for example, models B16 and C16. For switch B16, the range of the trip of the electromagnetic release will be 16 x (3-5) = 48-80 A. Accordingly, for the C16 machine this range will be within 16 x (5-10) = 80-160 amperes. Thus, in the presence of a current of 100 A, the B16 model will instantly turn off, and the C16 device will shut down only a few seconds after the bimetallic plate has been heated.

For residential and office buildings, the most suitable options  automatic machines with markings B and C are considered. This is due to the lack of large starting currents and extremely rare switching on of high-power electric motors. Machines of category D are used mainly on those facilities where there are powerful electric motors and other devices with large starting currents.

The timing of the current characteristic necessarily takes into account the temperature of the protective device itself. In the case of the first time tripping, more time is expended as the bimetallic plate is cold. When the trigger is repeated, when the plate has already been warmed up, the shutdown occurs faster.

Time-current characteristic curve

This chart shows the time current characteristics  for various types of circuit breakers - B, C and D. The main parameter is the value of the current flowing through the protection device, and has a direct effect on the tripping time. The ratio of the current flowing in the circuit and the rated current of the machine is displayed as l / ln on the X axis. The device response time, measured in seconds, is fixed on the Y axis

Since each automatic device consists of an electromagnetic and thermal release, the presented graph is conventionally divided into two sections. On the steep section, the work of the thermal trip unit is protected, which protects against overloads, and in the more shallow part the action of the electromagnetic release is shown, which performs a trip in case of short circuits.

The graph clearly shows that under different loads, the time for switching off the device also changes. The shutdown time at the same load for a cold and hot machine will be different. Thus, the graph of the time-current characteristic allows all necessary calculations  and choose the most suitable protective device  for specific operating conditions.

Selection of the machine for the house

For most apartments, category B automatic circuit breakers with increased sensitivity are recommended. Its operation at overloads occurs in the same way as for a Type C machine. However, in the event of a short circuit, their actions may differ.

Ideal conditions are the presence of a new house, a good network condition, the location of the substation near the facility. Of great importance is the quality of all connections. In such a situation, in the event of a short circuit, even the input automaton can work.

Quite different conditions in old houses. Typically, they are very old wiring, which has a high resistance. The current may not be sufficient, and in the event of a short circuit, the machine will not work. At such facilities, the time-current characteristic of the circuit-breaker must necessarily correspond to category B. This condition applies not only to apartments, but also to dachas and old rural houses.

Compared to conventional switches, automatic switches are placed in switch cabinets and are designed to protect electrical wiring against short circuits and overloads during power surges. The marking of the circuit breakers on the housing contains their main characteristics. On them you can get a full picture of the device.

Circuit breakers: marking and symbols

There are many types of machines, for example, the old type - AE20XXX.

For example, for the AE2044 machine, the marking is deciphered as follows: 20 - development, 4 - 63 A, 4 - single-pole with a thermal and electromagnetic release. Devices differ in the characteristic black color of the carbolite body.

The labeling scheme for automatic machines is standardized. Its main purpose is to understand most clearly the basic parameters of the device.

The marking is read from the top to the bottom.

1. The manufacturer or trademark is Schneider, ABB, IEK, EKF.
2. The serial or catalog number (series AB200 S200U, SH200).
3. Time-current characteristic (A, B, C) and nominal in amperes (I nom.).
4. The maximum permissible values ​​of the tripping currents at the output current.
5. Class of current limitation.
6. The article of the manufacturer, by which you can find this type of machine by catalog.

The picture below shows how to label the ABB and Schneider circuit breakers.

The disconnect button is marked or marked in red. If it is only one and is pressed, the depressed position means that the circuit is closed.

The marking of circuit breakers from the main manufacturers contains QR codes, where all information about the model is reflected. Their availability is a kind of quality guarantee.

The influence of environment

1. The temperature range for conventional models is from -5 ° C to +40 ° C. To work beyond these limits, special models are produced.
2. It is allowed to operate the apparatus at a relative humidity of up to 50% at 40 ° C. With decreasing temperature, the permissible humidity increases (up to 90% at 20 ° C).

Types of automata

Automatic machines are selected depending on the scheme of the electric system.

1. A single-pole automatic device

Devices are used in single-phase networks. The phase is connected to the upper terminal, and the load to the lower terminal. The device is connected to the phase wire break to disconnect the power from the load in the event of an emergency.

2. Two-pole automatic device

Structurally, the device is a block of two unipoles connected by a lever. The interlocking between the shutdown mechanisms is performed in such a way that the phase is disconnected before zero (according to the rules of the SAE).

3. Three-pole automatic device

The device serves for simultaneous power failure in the event of an accident. The three-terminal network combines 3 single-pole networks with a setting for simultaneous operation. Electromagnetic and thermal releases are performed separately for each circuit.

Circuit Breaker: Specifications

Automatic machines can have different time-current characteristics:

a) current-dependent;
b) independent of the current;
c) two-stage;
d) three-stage.

On the shells of most machines, you can see the uppercase Latin letters B, C, D. The marking of the circuit breakers B, C, D denotes a characteristic reflecting the dependence of the response time of the machine on the ratio K = I / I nom.

1. B - thermal protection operates in 4-5 s when the nominal value is exceeded by 3 times, and the electromagnetic protection is triggered after 0.015 s. The devices are designed for loads with small values ​​of the starting currents, in particular for lighting.
2. C - the most common characteristic of machines that protect electrical installations with moderate
3. D - automatic machines for load with high starting currents.

The peculiarity of the time-current characteristic is that for identical values ​​of the automata of types B, C and D, their disconnections will occur at different current excesses.

Other types of automata

1. MA - without thermal release. If a current relay is installed in the circuit, it is sufficient to install the circuit-breaker only with short-circuit protection.
2. A - the thermal release trips when I exceeds the nominal value. in 1,3 times. The shutdown time can be up to 1 hour. If the rating is exceeded by 2 times or more, the current release releases after 0.05 s. In the event of failure of this protection, overheat protection operates after 20-30 seconds. The automatic device with characteristic A is used to protect the electronics. The devices with characteristic Z are also used here.

Criteria for the selection of automata

1. I nom. - exceeding which leads to the activation of the overload protection. The nominal is selected according to the allowable maximum current of the wiring, and then reduce it by 10-15%, choosing it from the standard series.
2. Tripping current. The switching class of the circuit-breaker is selected depending on the type of load. For domestic purposes, the most common characteristic is C.
3. Selectivity is a feature of selective shutdown. The automatics are selected according to the rated current, so that the devices on the load side first of all operate. First of all, protection is disabled in places where short circuits occur or the network is overloaded. The time selectivity is selected in such a way that the response time is longer for the automaton located closer to the power source.
4. Number of poles. The three-phase input is connected to an automaton with four poles, and to a single-phase input with one or two. Lighting and household appliances operate on single-pole networks. If the house has an electric boiler or a three-phase electric motor, three-pole automata are used for them.

Other options

When a circuit-breaker is purchased, the characteristics must be selected in accordance with the operating and connection conditions. Each machine is designed for a certain number of cycles of operation. As a load switch it is not recommended to use it. The number of machines is selected as needed. It is mandatory to install the introductory, and after it - on the lighting line, outlets and separately to powerful consumers. Mounting methods for different models may vary. Therefore, devices similar to those in the cabinet are chosen.

Conclusion

Marking of circuit breakers is required to select them in accordance with specific needs. Their characteristics are directly related to the section of the wiring and the types of load. In case of short circuits, first of all, electromagnetic releases are triggered, thermal overload is provided for prolonged overloads.

The time-current characteristic curve D of the circuit-breaker differs from B and C in that the rapid disconnection of the load current occurs in the range from 10 to 14 times the rated current of the circuit-breaker.
  The specificity of the time-current characteristic D is that the automata of characteristic D are used mainly in industry, for the protection of electric motors and their supply lines. Since at the start of the electric motor, it does not go directly to the nominal mode, but accelerates for a while, the starting currents during the acceleration of the motor significantly exceed the current consumed by the dive in normal, operating mode and can reach ten times the operating current, the C more B can not be used for such purposes, since this will lead to the impossibility of starting the electric motor in connection with the cut by the next start-up of the circuit breaker after exceeding the current.
  The D-Rating machine with a rating of 40 Amperes will not turn off when the motor starts, even if the inrush current reaches 400 amperes for less than 1 second, it can also not turn off at higher currents, in the case of an even shorter period of inrush current.

Characteristic D of the thermal trip of the circuit breaker

  The time-current characteristic curve D shows clearly that the thermal release, whose operating speed refers to a time greater than 15 milliseconds, allows non-breaking starting current up to three ratings for five seconds, five ratings for two seconds and ten ratings for one second . Considering that at start-up, the most powerful starting current is formed at the moment of power-up, and further, as the rotor of the engine is untwisted, tending to the rated current of the electric motor, then in the case of non-switching of the automaton at the first moment, which will speak of incorrect choice of the nominal value of the machine, then the further process of starting the electric motor will be normal and the circuit breaker will not shut down due to the starting current.

Characteristic D of the electromagnetic trip of the circuit breaker

  The electromagnetic release, whose operation is described by the lower part of the time-current characteristic curve D, is characterized by a high, millisecond, operating speed at high currents flowing through the coil of the release.
  The device and characteristics of the electromagnetic release time of the current characteristic D practically do not differ from the characteristics of the release for curve B and C, because in all versions of circuit breakers, the electromagnetic release serves to prevent a short circuit and is not tied to the current rating of the machine.

7-05-2012, 19:47 |

Modern household appliances have two overcurrent releases:
1. Thermal  (Bimetallic plate, which bends when heated by a flowing current and triggers the release mechanism) - triggers for prolonged overload, with inverse time delay: the greater the overload, the faster the bimetallic plate heats up and the shunt release operates faster.
The normalized parameters for B, C and D are as follows:
  - at a current of 1.13 denominations - TP does not fire within an hour.
  - at a current of 1.45 denominations - TP is triggered for an hour (two hours for AV of higher denominations).
  The dependencies of the pickup time on the frequency of the overload current - the time-current characteristics of AB - are given in the PDF in the attachment.

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View online file:
  In reality, AB C16 at 24A is switched off on average after 5-15 minutes.

2. Electromagnetic  (EMP) (solenoid with a core, at a certain current, the magnetic field of the solenoid retracts the core, which triggers the release mechanism) - instantly fires when the fault is shortened, so that the affected section of the network does not wait for the TP to warm up in the machine. Letters B, C, D, G ... in the designation of the machine in front of the nominal characterize the multiplicity of the EMP (cutoff) setting to the nominal value of the machine.
  The multiplicities are as follows:
  B - 3 ... 5
  С - 5 ... 10
  D - according to GOST R - 10 ... 50, most manufacturers declare a range of 10 ... 20.
  G - 6.4 ... 9.6 (KEAZ BM40)
  K - 8 ... 14
  L - 3,2 ... 4,8 (KEAZ BM40)
  Z - 2 ... 3
It should be noted that the performance of AB does not depend on the letters B, C, D ..., only the threshold of operation of the EMP changes.

For example: automata B16 and D16, the ranges of operation of EMP: 16 * (3 ... 5) = 48 ... 80A and 16 * (10 ... 20) = 160 ... 320A respectively.
  At a current of 150A, the B16 automaton switches off instantaneously, and D16 - in a few seconds, when the bimetal is heated.
  At a current of 1000A both automata will work instantly.
  It should be noted that due to the fact that the EMP is triggered almost instantaneously, all short-range and high-voltage machines with a high probability will operate simultaneously with a high probability (if TKZ reaches the threshold for their EMR).

The most common are automata with the characteristic C, also types B and D are often encountered.
"FROM"  suitable for most household and general industrial applications when feeding loads with small and medium starting currents.
"AT"  have a more sensitive EMP, so their use is particularly preferred in "shabby" networks with small expected TKZ. These ABs work steadily with an absolute majority of household loads (i.e., there are no false positives due to starting currents).
"D"  have a reduced sensitivity at short-circuit and can be recommended for use as inputs to increase the chances of selectivity with downstream group AB at short-circuit. To protect the group lines, they should be used only in justified cases with large starting currents of loads.