No, dear reader, today we will not talk about the choice of the manufacturer, although, I will not hide, I am not indifferent to this trinity, which is in the photo. Today I will try to tell you how to choose the parameters of machines based on the conditions of their use. The choice of circuit breakers must be approached as responsibly as possible, since it is these modest workers of the power grid who take the brunt in most emergency situations.
Any serious manufacturer (well, or one who wants to appear serious) indicates several obscure, but very important designations on the front side of the machine gun case. Let's look at the pictures:
The numbers 1,2,3 mark the same type of designations on the machines different manufacturers. What are they talking about? Let's sort it out in order. If some words and abbreviations are not clear, take a look at. And be patient, dear reader, the article will be long. So:
NUMBER 1
In the photographs, the number 1 indicates the rated current of the machine, measured in amperes. This is the most important parameter of the circuit breaker. We do not pay attention to the letter to the left of the rated current, more about it later.
What exactly is a circuit breaker for? That's right, for protection, but protection of what? May be, household appliances? No. He is not required to protect household appliances. The machine protects the wiring. And it is precisely that section of the wiring that is connected AFTER the machine, and not BEFORE it. Wiring can be made with a cable of different sections, respectively, and a long current can withstand different. The task of the machine is to prevent the continuous flow of current that exceeds the value allowed for a given cable. What do the PUEs say about this?
Table 1.3.4. Permissible continuous current for wires and cords with rubber and PVC insulation with copper conductors| Conductor cross section, mm 2 | Current, A, for wires laid | |||||
| open | in one pipe | |||||
| two single core | three single core | four single core | one two core | one three core | ||
| 1,5 | 23 | 19 | 17 | 16 | 18 | 15 |
| 2,5 | 30 | 27 | 25 | 25 | 25 | 21 |
| 4 | 41 | 38 | 35 | 30 | 32 | 27 |
| 6 | 50 | 46 | 42 | 40 | 40 | 34 |
| 10 | 80 | 70 | 60 | 50 | 55 | 50 |
| 16 | 100 | 85 | 80 | 75 | 80 | 70 |
I edited the table, removing sections from it that are not used in everyday life. The conditions for cooling the cable laid in the strobe are practically the same as when laying in the pipe. A three-core cable with a PE protective conductor must be considered here as a two-core cable, since no current flows through the protective conductor in normal operation. Therefore, we are interested in the penultimate column of the table (highlighted in red), which indicates the permissible continuous currents for a two-core cable laid in a pipe. Everything seems to be clear; we protect a cable with a conductor cross section of 1.5 squares with a 16A machine (the closest standard rating to the lower side is from 18A), 2.5 squares - 25A and so on ...
But it was not there! It was in the USSR that you could buy a cable with a cross section of 2.5 square meters declared by the manufacturer and be 100% sure that this is the case. Now, "effective managers" are ready to do anything to extract additional benefits. And the vast majority of cable products come with an underestimated cross section of the cores. Let's say you bought a cable with a cross section of 2.5 squares, measured the core diameter with a micrometer, calculated the area of the circle and realized that, to put it mildly, you were deceived. The real cross section of the core turned out to be, for example, 2.1 squares.
But that's not all. Did you sell the cable as copper? Electrical copper should be of a reddish hue, easy to bend and not springy. Now look what you have in your hands. The cores have a yellowish tint, bend with effort and clearly spring? Congratulations . The manufacturer also saved on chemical composition lived. It is no longer copper, but rather brass. And the electrical conductivity of brass is lower than that of copper.
What to do? Well, first of all, not all manufacturers cheat. There is, for example, "Rybinskelektrokabel" or Kolchuginsky "Elektrokabel", which produce honest GOST products. True, it will be more expensive. And you won’t be able to buy it in Yaroslavl with a swoop, you have to order it. If necessary, we will do it, I have a discount. If you need it cheaper, you can buy it in specialized stores, the cable there is also of quite acceptable quality, there is no outright leftist. The main thing is not to buy cable in greengrocer stores selling everything from flower pots to cars.
But back to the topic of our conversation. Let's say the cable you purchased is, let's say, not entirely honest. Nothing wrong with that. It is only necessary to reduce the nominal value of the machine by one step. For example, if according to table 1.3.4 for a cable with a conductor cross section of 2.5 squares, the allowable current is 25A, then we will supply an automatic machine with a nominal value of 16A. For a cable with 6 square conductors, the table allows 40A, but we will install a 32A machine. In short, it's better to play it safe. But it's not just about reinsurance. There is another good reason to reduce the nominal value of the machine by one step from the table value. About her later.
Let's briefly summarize this part of the article, bringing the cross section of the cable cores and the rating of the circuit breaker into line, taking into account reasonable reinsurance and scope:
We continue the conversation about the number 1 in the pictures. Now let's talk about the letter to the left of the designation of the rated current of the machine:
This letter indicates the characteristics of the electromagnetic (instantaneous) release. Whoever is not familiar with the circuit breaker device and does not know what an electromagnetic release (EMR) is, please. EMR is triggered when a short circuit current (SCC) occurs. But the machine must be able to distinguish shorty from overload. For example, a current of 25A went through a machine with a nominal value of 16A. This is an overload, but not a short circuit current. The bimetal plate of the thermal release (TP) heats up and causes the machine to turn off. But this takes time, TR does not know how to work instantly. And if the current is not 25, but 200A? Now it already looks like a shorty. As long as the TR works, a fire may start! This is where the EMR comes into play, which will cause the machine to turn off immediately.
Where is the boundary beyond which the EM should regard the overload as a short circuit and instantly turn off the machine? This border is indicated by the letter to the left of the designation of the rated current of the machine. It is called the characteristic of the electromagnetic release. This letter indicates the multiplicity of the cut-off current EMR (Iots) in relation to the rated current of the machine (In). That is, the ratio Iots / In . These letters may be different, but there are three most common ones:
Letter "B". Iot=3…5In
Letter "C". Iot=5…10In
Letter "D". Iot=10…20In
Let's look at two examples:
Example one. A circuit breaker with a rated current of 16A and characteristic "C" (C16) went through a current of 100A. Will the cut-off (EMR) work or will the machine need time to trigger the TR? We multiply the rated current of the machine by the multiplicity factor corresponding to the characteristic "C" (in calculations, for reliability, you should use the largest value of the multiplicity factor from the range for the corresponding characteristic; if for the characteristic "C" the range is 5 ... 10, in the calculations we take the value of the coefficient equal to 10) :
16x10=160A
The electromagnetic (instantaneous) release of the C16 machine will operate at a current not less than 160A. But we have a current through the machine is 100A. Means what? That's right, the EMR in this example will not work and the only thing left to hope for is TR.
Second example. The conditions are the same as in the previous example, but the EMR characteristic is no longer “C”, but “B” (automatic machine B16):
16x5=80A
The minimum operating current of the EMR in this case is 80A. We have 100A. Therefore, we have a margin of 20A and the cutoff will work confidently; the machine will turn off immediately.
For clarity, I stole the following picture from the Internet:
The picture is called "Time-current characteristic of the circuit breaker". Knowing how many times the current through the machine is greater than its nominal value, it is possible to determine the response time from it. In the picture, the area of operation of the electromagnetic release is indicated in light gray, and above it - the thermal one, the color is darker. Again a few examples:
1. The current through the machine is twice its nominal value. It follows from the picture that the machine with any characteristic will turn off in the time interval from 10 to 50 seconds.
2. The current through the machine is eight times the rated current. The machine with characteristic "B" will turn off in 0.01 seconds, the EMR will work. And the machine with characteristic "C" will work in the time interval of 0.01 ... 3 seconds. Remember the cutoff current multiplicity interval 5 ... 10In for the “C” characteristic? In our example, we have an eight-fold overload lying inside this interval. Therefore, the response time will depend on the specific instance of the machine. For one machine, the EMR will work (0.01 seconds), for the other it will not, and the machine will have to be turned off by the thermal release in 3 seconds.
3. The current through the machine is 15 times higher than the nominal one. Here, automata with characteristics “B” and “C” will work instantly, and an automaton with characteristic “D” (cutoff current multiplicity interval 10 ... 20In) can work instantly, or maybe think for 2 seconds. Again, this will depend on the particular instance.
4. Thirty times the rated current. Specific shorty! In this case, all three machines ("B", "C" and "D") "clack" immediately.
But that's not all the "interestingness" of this picture. See in the upper left corner two lines going up and next to them two numbers - 1.13 and 1.45? These are very interesting numbers. These are overload multipliers at which the machine operates in more than an hour (1.13) and less than an hour (1.45). In other words, if the overload is less than 1.13, then the machine will not work at all. If in the range from 1.13 to 1.45, then it will work in more than an hour. And if the multiplicity of overload is more than 1.45, for example, 1.6, then the machine will work in less than an hour.
Let's go back a little, to the choice of the rated current of the machine. Remember table 1.3.4? Let's calculate what will happen if we blindly use this table and do not think with our heads. For a cable with 2.5 kV conductors, when laying in a strobe, the table allows a continuous current of 25A. We turn off our brains and stupidly put a 25A machine on this line. And then we arrange an overload; Let's say 1.4 times. 25x1.4=35A! And the time-current characteristic tells us that the machine will take more than an hour to operate with such an overload. That is, for more than an hour a current will flow through the cable almost one and a half times the maximum allowable! And if, in addition, the cable is laid in such a way that its cooling conditions are unimportant, for example, in a corrugation or in a layer of insulation, or both at the same time? We also do not forget about the fact that the cable, possibly with an underestimated cross section, has lived. What will happen in the end? Let's fry the cable! Fire, most likely, will not happen, but insulation degradation will inevitably occur, which will make itself felt in a few years. And if such overloads occur regularly, then much earlier. This is another reason to reduce the nominal value of the machine by one step from the table value. Hello to you, jamshuts, sculpting 25A machines for socket lines! I repeat for you:
1.5 sq. mm. - 10A. Lighting lines.
2.5 sq.mm. - 16A. Outlet lines.
4 sq. mm. - 25A. Lines of instantaneous water heaters of moderate (up to 5 kW) power.
6 sq. mm. - 32A Lines of electric stoves or instantaneous water heaters of high power; entrance to apartments with gas stoves.
10 sq. mm. - 50A. Entering apartments with electric stoves.
By the way, there is one more nuance. Most conventional household outlets are designed to be connected to 2.5 square wires. But the allowable current indicated on the outlet is 16A. Therefore, the machine must also have a rating of not more than 16A, despite the fact that table 1.3.4 allows a continuous current of 25A for a cable with 2.5 square conductors. Household appliances that have a regular plug designed to be plugged into a regular outlet never have a power of more than 3.5 kW, which means that they easily fit into the 16A limit.
But back to the characteristics of the electromagnetic release. How to choose the right letter to the left of the rated current of the machine? It is clear that it is necessary to strive to ensure that the EMR of the automaton reliably operates in the event of a SCC. In other words, the product of the rated current of the machine and the multiplier must be obviously less than the TKZ that may occur in the protected section of the network. And the higher the TKZ, the more confidently the machine will work. But what does the expected TKZ depend on? Just three factors:
1. The length of the network. The greater the distance from the transformer substation to your home, the farther your entrance from the house ASU and the higher your floor, the lower the expected TKZ.
2. Cross section of conductors. If the risers of your house are laid with aluminum wires with a cross section of only 6 squares, and in the apartment there are “noodles” of APPV with a cross section of 2.5 squares, you should not count on a large TKZ.
3. Status of connections. A bunch of "snotty" twists in floor boards will also reduce the expected TKZ.
There are special devices for measuring the expected STC. Their price tag is inhumane, so they are not available to most home craftsmen. But when choosing the characteristics of an electromagnetic release, you can be guided by a few simple rules:
Characteristic "B". It is preferable in the old housing stock, where the reconstruction of intra-house electrical networks has not been carried out. Also, in rural and country houses, receiving power from overhead lines with a large length. Here it should be noted that the price of machines with characteristic "B" is slightly higher than with characteristic "C" and they are not on free sale, a custom item. But again, dear reader, if necessary, we will do it.
Characteristic "C". Machines with this characteristic are the most common and commercially available. They can be used in electrical networks that are in a satisfactory condition.
Characteristic "D". Due to the large cutoff current ratio (10 ... 20 In), such automata are used in industry to protect lines with large starting currents that occur, for example, when starting powerful electric motors. And they have no place in everyday life! Here is what GOST 32395-2013 "Distribution boards for residential buildings" says:
"6.6.5 Circuit breakers ..... must have short-circuit releases (electromagnetic, types B, C)"
As you can see, the characteristic "D" in residential buildings is not allowed.
Well, dear reader, we figured out the rated current of the circuit breaker and the characteristics of the electromagnetic release. Now let's move on to number 2 in the pictures.
NUMBER 2
In the photographs, the number 2 indicates the breaking capacity of the machine (OS), measured in amperes. This is the maximum short-circuit current that the machine is able to turn off while maintaining its performance. Above, I said that in the old housing stock, in rural areas and in summer cottages, the expected TKZ does not reach large values, and to ensure protection, it is necessary to use machines with characteristic "B", that is, with more sensitive EMR capable of responding to relatively small short circuit current.
But the situation can be just the opposite. If you have a new building apartment, risers in the entrance of a large section, and the substation is located right in the yard, the expected TKZ can reach very large values, up to 2000 ... 3000A! The machine will certainly work, but when its contacts diverge, a powerful arc will arise between them, which will have to be extinguished immediately. Here, the ability of the machine to extinguish the arc caused by a short circuit is indicated by its breaking capacity.
Breaking capacity can be 3000, 4500, 6000 and 10000A. By the way, machines with OS 3000 and 4500A are prohibited for use in the EU countries. Automatic machines with OS 3000A are no longer produced by European firms; 4500-amps are produced, but sold only in the CIS. Actually, there is no crime in this; breaker with breaking capacity 4500A is suitable for residential use. Here is a machine from ABB model SH201L with OS 4500A:
This series at ABB is called "Compact Home", that is, it is intended for use in residential construction.
But I still prefer to use automatic machines with a breaking capacity of 6000A. The fact is that the higher the breaking capacity of the machine, the greater its resource. And given that the difference in the price of machines with OS 4500 and 6000A is only about 20 rubles, meager savings on their own security are inappropriate.
And finally, dear reader, we got to the number 3 in the pictures.
NUMBER 3
The number 3 on the pictures indicates the current limiting class. What is it?
Let's imagine how the machine works when a short circuit occurs:
1. The short circuit current causes an increase in the magnetic flux in the coil of the electromagnetic release.
2. The core of the coil moves under the influence of its magnetic field and stimulates (provokes) the disengagement mechanism of the contact group.
3. The trip mechanism operates and opens the contacts.
4. The arc formed between the contacts is extinguished by the arc chute.
It is clear that each of these four stages takes some time. But we have a short man and a huge current flows in the emergency line! This means that the response time of the machine should be as short as possible; the less this time is, the less trouble the shorty will have time to do. And it is very desirable that the machine work before the short-circuit current reaches its maximum value.
An automaton with current limiting class 2 operates in no more than 1/2 half-cycle. And an automaton with class 3 works faster, no more than 1/3 of a half-cycle and, of course, is more preferable. Note that in the second case (class 3), the machine will trip before the short circuit current reaches its maximum.
To increase safety, the electrical wiring in the apartment must be divided into several lines. These are separate machines for lighting, kitchen outlets, and other outlets. High-power household appliances with increased danger (electric water heaters, washing machines, electric stoves) must be turned on through an RCD.
Convenient installation of machines in the shield
The RCD will react in time to the current leakage and turn off the load. For the right one, it is important to take into account three main parameters; - rated current, switching capacity of breaking the short-circuit current and the class of automata.
The calculated rated current of the machine is the maximum current that is designed for continuous operation of the machine. At a current higher than the rated current, the contacts of the machine are disconnected. The class of automata means a short-term value of the starting current, when the automaton does not work yet.
The starting current is many times greater than the rated current value. All classes of machines have different excesses of the starting current. In total there are 3 classes for machines of various brands:
- class B, where the starting current can be more than the rated current from 3 to 5 times;
- class C has an excess of the nominal current by 5 - 10 times;
- class D with a possible excess of the current of the rated value from 10 to 50 times.
Circuit breaker marking
In houses, apartments, class C is used. The switching capacity determines the magnitude of the short-circuit current when the machine is instantly turned off. We use automatic machines with a switching capacity of 4500 amperes, foreign automatic machines have a short-circuit current. 6000 amps. You can use both types of machines, Russian and foreign.
Circuit breaker calculation
You can choose machines based on the load current or the cross section of the wiring.
Calculation of the machine for current
We calculate the total power of the loads on the machine. We add the power of all consumers of electricity, and according to the following formula:
we get the rated current of the machine.
P is the total power of all consumers of electricity
U - mains voltage
We round the calculated value of the received current up.
Calculation of the machine according to the cross section of the wiring
To select the machine, you can use table 1. The selected current is reduced to the lower value of the machine's current to reduce the load on the wiring.
Choice of rated current according to the cable section. Table #1
For sockets, the machines take 16 amperes for a current, since the sockets are designed for a current of 16 amperes, for lighting the best option for a 10 ampere machine. If you do not know the cross section of the electrical wiring, then it is easy to calculate it using the formula:
S - wire section in mm²
D - wire diameter without insulation in mm
The second method of calculating the circuit breaker is more preferable, as it protects the wiring diagram in the room.
Circuit breakers are designed to protect electrical wiring from overloads and short circuits. It is a mistake to believe that when choosing an electrical appliance, you need to be guided by indicators of the load on the network. The machine protects cables and wires, and not connected household appliances.
With an increase in the load on the electrical network, the current strength increases, due to which the wires begin to heat up, and the insulation melts. At this point, the circuit breaker trips. The current stops flowing to this section of the circuit, because. the electrical device opens it. Automatic switches are placed at the input.
Types of machines
Types of circuit breakers are distinguished by releases. The release is a structural element of the machine, which is entrusted with the main function of breaking the power supply in the event of an increase in voltage.
- Electromagnetic releases - instant response and operation of the machine. Principle of operation: when the current increases, the core retracts in hundredths of a second, thereby tensing the spring, which causes the releases to operate
- Thermal bimetallic releases - a network break occurs only if the limit values \u200b\u200bof the cable parameters are violated. The principle of operation is to bend the plate when it is heated. She pushes the lever in the machine and it cuts out
- Semiconductor releases - used on the AC / DC mains at the input. The work on breaking the line is carried out by the relay unit of the transformer
Overload sensitivity characteristics
First you need to pay attention to the main characteristics of the operation:
- Characteristic A - for electrical wiring with particularly sensitive equipment. Calculation for the instantaneous response of the machine to overload
- Characteristic B - to protect electrical wiring (sockets and lighting) from the load in residential buildings. A slight delay in the operation of the machine when the current increases by 3-5 times from the nominal value
- Characteristic C - for protecting electrical wiring from load in residential buildings and for networks with high starting current. The most common feature. The machine does not respond to small voltage surges, but only works in case of serious overloads - an increase in current strength by 5-10 times from the nominal value
- Characteristic D - to protect the wiring from a load with a large starting current. Installed at the input to control the electrical network of the entire building. Turns off the network when the current increases by 10-50 times from the nominal value
The choice of the machine by the number of poles
Depending on the purpose of the machine, the number of poles of the machine is chosen:
- Single-pole - to protect lighting and sockets
- Bipolar - to protect powerful household appliances ( washing machine, electric stove, etc.)
- Three-pole - to protect generators, borehole pumps, etc.
- Four-pole - for protection of a four-wire network
The choice of the machine by power
The selection of the circuit breaker is based on the rated current. To calculate it, you need to use the generally accepted formula:
Where: I is the amount of current
P - power of all electrical appliances in W
U - mains voltage in V (usually 220V)
In addition to choosing a circuit breaker by power, it is necessary to take into account the calculation of the maximum operating current. The rated current must be greater than or equal to the maximum. To calculate, you need to sum up the power of all devices and divide it by the voltage in the network, multiplied by the reduction factor.
Depending on the type of wiring, the calculation of the limit values:
- For aluminum wires - up to 6A per 1 square millimeter
- For copper wires- up to 10A per 1 square millimeter
When installing a circuit breaker, you must also take into account the multiplying factors. They are calculated from the number of electricity consumers:
- Number of consumers 2 -0.8
- Number of consumers 3 - 0.75
- More than 5 consumers - 0.7
In addition to increasing ones, reduction factors are also used for calculation: the difference between the total and consumed power. Value 1 - for simultaneous connection of several household appliances and 0.75 - if Appliances there is, but due to the lack of outlets, they cannot be turned on at the same time.
After the calculation, you need to check the table for the maximum allowable current value for the conductor:
Basic rules for choosing machines
- You need to buy a machine in specialized stores
- When choosing a manufacturer, give preference to the most famous and reliable
- You can not buy machines with a damaged case
- The choice of the machine must correspond to the parameters of the electrical wiring after calculating the power
- For old electrical wiring, in which aluminum wires were used, you can use an automatic machine no more than 16A, or two 16A each if there are two outgoing wires. It is impossible to turn on several types of household appliances at the same time
Modern systems for protecting electrical wiring from burnout and ignition involve the use of circuit breakers and are divided according to the type of network into single-phase and three-phase. In the private sector, in most cases, devices of the second type are used, so the correct calculation of the machine for power for 380 volts becomes relevant, which ensures the reliability and durability of the use of the electrical network.
Appointment and work
The first automatic device designed to protect electrical circuit from overcurrents, was invented by the American scientist studying electromagnetism, Charles Grafton Page in 1836. But only 40 years later, a similar design was described by Edison. . The modern type of protective devices was patented in 1924. Brown, Boveri & Cie Corporation of Switzerland.
The innovation of the design was the reusability of use due to the ability to turn on the module when it is triggered by pressing one button. The advantages over fuses were undeniable, while the accuracy of the machine was much better. When using the device in a network designed for 380 volts, all phases are turned off at once. This approach avoids the distortion of signal levels and the occurrence of overvoltages.
The direct purpose of a three-phase circuit breaker is to turn off the line when a short circuit occurs in it or when the power consumption of the devices is exceeded. Protection modules belong to the group of switching equipment and due to their simple design, ease of use and reliability, they are widely used in both domestic and industrial power networks. Usually the device assumes manual control, but some types are equipped with an electromagnetic or electric motor drive, which makes it possible to control them remotely.
Some users mistakenly assume that the machine protects the devices connected to it, but in fact this is not the case. It does not react in any way to the types and types of devices connected to it, and the only reason for its operation is overload and overcurrent. At the same time, if the machine does not turn off the line, the electrical wiring will begin to heat up, which will lead to damage or even ignition.
The choice of an automatic protection module is associated with the ability of an electric line to withstand a current of a certain value, which is directly related to the cable material and its cross section. In other words, when choosing a module, the main parameter is the power or maximum current, which leads to the operation of the machine.
Protection module design
Despite the wide range of products offered by various manufacturers, the designs of circuit breakers are similar to each other. The body of the device is made of a dielectric that is resistant to temperatures and does not support combustion. On the front panel there is a manual control lever, and the main technical characteristics are also applied.
Structurally, the body consists of two halves, twisted together by bolts. In the middle of it are the following elements:
It is the designs of the releases that provide almost instantaneous operation of the circuit breaker. An electromechanical contact reacts to the occurrence in the circuit it protects of a current whose parameters exceed the nominal value. The design of the release includes an inductor with a core, the position of which is fixed by a spring, and already it is connected to a movable power contact. The solenoid windings are connected in series with the load. The thermal release is a compressed strip of two metals with different thermal conductivity (bimetallic plate).
Operating principle
After connecting the power and load electric lines to the three-phase machine, it is turned on by moving the lever to the upper position. As a result, the lever engages through the latch with the closing contact. The formed connection is provided due to the displacement of the movable contact group relative to their holder.
Under normal circumstances, the current flows through the contact between the power contact and the moving contact. Then it enters the bimetallic plate and the solenoid winding, and from it it already gets to the terminal and the load connected to the machine.
If a current with a value exceeding the allowable value begins to flow through the switch, then the bimetallic plate begins to heat up. Due to the different thermal expansion of the metals, it bends, eventually breaking the contact. The strength of the current at which the connection breaks depends on the thickness of the plate. The thermomagnetic release is characterized by slow operation, although it can even fix minor changes current values. Its setting is carried out at the factory by changing the distance between the plate and the moving contact. For this, an adjusting screw is used.
But for a current that instantly increases its value, the reaction rate of the bimetallic plate will be extremely low, so a solenoid is used along with it. In the normal state, the core is pushed out by the spring and closes the contact of the machine. With an abnormal value of the signal in the turns of the coil, the magnetic field rapidly increases, the flows of which draw the core inward, overcoming the action of the spring, and this leads to a circuit break.
The operation of the electromagnetic release occurs in a fraction of a second, while it does not react to currents slightly exceeding the rated ones. Simultaneously with the disconnection of the entire three-phase line, the lever also drops, which again needs to be moved to the upper position to connect the load to the network.
Device specifications
The correct selection of a 3-phase machine is not only in determining the conditions for its operation, but also in terms of power and type of load that will be connected to it. Incorrectly selected power of the module leads to a deterioration in the protection of the electrical wire, while such a device itself can become a source of an emergency.
But still, no matter how important it is to choose the right power, automatic devices are also characterized by other technical parameters that affect their operation. The main ones include:
In addition to technical parameters, automatic devices are also characterized by quality indicators. The most common ones include the type of drive, the method of connecting external conductors, the cut-off design, and others.
Power selection
There are two ways to determine the required power for a 3-phase machine. At the same time, one complements the other, and does not exclude it. The first method is associated with finding the total value of the energy consumed and the load, and the second - with the cross section of the electrical wiring.
Based on the definition that the machine does not protect the equipment, but the electrical wiring, it is necessary to select the power, focusing on the parameters of the latter. This is true, but only until the network upgrade is planned. For example, the existing wiring in the house is designed for 1.5 squares. According to technical specifications copper wiring of this diameter can withstand a long-term current of not more than 10 amperes. Accordingly, the maximum simultaneous energy consumption of devices connected to the machine output should not exceed 3.8 kW. This value is obtained from a simple formula for finding power - P \u003d U * I, where:
- P - the highest allowable power consumption, W;
- U - voltage of a three-phase network, 380 volts;
- I is the maximum current that the wiring can withstand, A.
The resulting number indicates that the total load connected to the line at the same time should not exceed this value, i.e. when the 2 kW boiler is turned on, nothing bad will happen. But if you connect a 3 kW electric furnace to this line, then the wiring will not stand it and catch fire, therefore, to prevent an accident, you must install a 10 A automatic machine, which allows you to load the line up to 2.2 kW.
The advantage of using a three-phase machine is that three lines can be connected to it at the same time, while the value of the rated current will be determined by summing the powers of all phases. Thus, for a 380 volt machine, it will be 6.6 kW, and in the case of connecting a triangle-type load, it will be 11.4 kW. That is, for the given example, if it is not possible to separate the line to different phase outputs of the protection device, you will need to purchase a 6 A machine.
If it is planned to upgrade the wiring or use a thick cable, then the calculation can be made based on the power consumption of the load. For example, if the load of each phase does not exceed 4 kW, then the rated current is calculated as the sum of the powers plus 15–20% of the margin (I \u003d 4 * 3 \u003d 12 A + margin \u003d 14 A), so the most suitable device in this case will be an automatic at 16 A.
Nuances in the calculation
To simplify the determination of power as a margin, it is customary to use not a percentage, but a multiplication by a coefficient. This additional number is considered to be equal to 1.52.
In practice, it is rarely possible to load all three phases equally, therefore, when one of the lines consumes a lot of energy, the circuit breaker rating is calculated based on the power of this particular phase. In this case, it takes into account highest value consumed energy and multiplied by a factor of 4.55, and then it will be possible to do without the use of tables.
Thus, when calculating the power, first of all, the parameters of the electrical wiring are taken into account, and then the energy consumed by the protected automatic machine of the electrical equipment. Here, the correct remark from the rules for the installation of electrical installations (PUE) is taken into account, indicating that the installed circuit breaker must protect the weakest section of the circuit.
A circuit breaker, also known as a switching protective device, is a device that protects a building (in particular, the electronics in it) from electric shock.
Under normal operating conditions, when all equipment and wiring are operating normally, current flows unhindered through the circuit breaker. But as soon as the current strength exceeds the critical level (the load has increased as a result of malfunctions in the operation of devices or electrical circuits and a short circuit has occurred), the releases are activated in the switch and the network opens.
As a rule, the described devices are equipped with two types of releases:
In the absence of a circuit breaker, an emergency can cause overcurrent to flow through the network, the insulating material to melt, and the wiring itself, most likely, to catch fire. The consequences can be the most deplorable - from a fire (especially for wooden structures, such as a bathhouse) to electric shock. In today's article, we will talk about how to choose a circuit breaker depending on the wire section, current and other parameters.
Note! If we are talking about the idea of \u200b\u200breplacing an old device, then you just need to study its marking and, when choosing, focus on it. But if you plan to install a switch, for example, in a newly built building, then all parameters should be selected independently.
The selection and installation of machines is regulated by the Rules for the installation of electrical installations (PUE).
PUE, section 7. "Electrical equipment of special installations". Chapter 7.1. Download file
circuit breaker
To choose a device that is suitable both in terms of technical characteristics and cost (although the second indicator is not critical, since the price of such equipment is insignificant), you need to go through a few simple steps.
Note! The cost of a single-pole machine (and there are also three-pole ones) varies between 50-200 rubles. For a medium-sized bath, about 5-7 poles may be required, therefore, the protection itself will cost about 250-1500 rubles. Agree, not such a big amount for electrical safety for 15 years.
Step one. Place of purchase
First, you should make sure that the device itself is safe. It is advisable to buy the switch in a specialized store, and not in the market or in a dubious outlet. You should also ask the seller about the manufacturer and origin of the device, ask to present the relevant documents. As you know, cheap products from China are often not only useless, but even dangerous.
Yes, it costs more, but the quality will also be high, since large corporations are unlikely to risk their reputation. Now - directly to the specific parameters.
Step two. Cable section
It is worth remembering that, in fact, the switch does not protect the electrical equipment connected to the network, but the wiring. Cross-sectional selection should be carried out if the wiring has been laid for a long time. In such cases, you just need to adjust to specific conditions.
First, the cross section of the wire is measured and determined. For further actions, you can use the corresponding table.
Table. The dependence of the limiting current on the cross section
| Cross section, mm.sq. | Copper core | Aluminum core |
|---|---|---|
| 1 | 17 | - |
| 1,5 | 22 | - |
| 2 | 26 | 21 |
| 2,5 | 30 | 23 |
| 3 | 33 | 27 |
| 4 | 40 | 32 |
| 6 | 51 | 40 |
| 10 | 80 | 56 |
When the current value is determined, it is necessary to select the type of circuit breaker from it. It is worth noting that in parallel it is recommended to determine the maximum power of devices that are connected to the network. The fact is that, for example, the wiring can withstand the connection of one heat generator, and if there are several of them at once, the cables will start to heat up, which sooner or later will cause a short circuit.
It is from the bandwidth of the wiring and the total power of the connected equipment that the first indicator will depend - the operating current of the switch (it is also called the rated current).
Step three. poles
Modern switches can be single- and three-pole, let's get acquainted with each of the varieties.
Step four. Overload current
The overload current of the device is also very important. If we are talking about a single-phase network, then when choosing a switch, one should be guided by the following calculations: let's assume that 10 kilowatts are allocated to the room, therefore, 10,000 watts must be divided by 220 volts (voltage). The result - 45.5 - is rounded down to a lower value, in this case it is 40 amperes.
With a three-phase network, slightly different calculations are carried out. The formula to be used is as follows:
P / U x 1.7 \u003d I
In this case, P is 3,000 watts, U is 380 volts, 1.7 is the root of three, and I, respectively, is the required current. If you make calculations using this formula for the room given as an example, it turns out that you will need the same device for 40 amperes, but already three-pole.
Three-pole circuit breaker BA47-100 ТМ UNIVEC
Based on these calculations, one of several possible types is selected (it all depends on the purpose of the application):
- At 3.4 or 5- used for resistive loads with grounding (such as sockets, lighting);
- Z 2-3– suitable for electronics;
- From 5-10- required to protect low-pulse current electrical circuits (this includes both residential buildings and offices);
- By 8-15– suitable for powerful transformers and electric motors;
- D 10-20– suitable for conditions of high impulses and switching current (lifting devices, pumps, transformers, etc.).
Step five. Short circuit (short circuit)
When choosing a model for short-circuit current, you need to remember one thing important condition: in accordance with the rules of the PUE mentioned above, the use of machines with a power of less than 6 kA is prohibited. Today, protective devices can have the following ratings (kA):
Note! If the room in which the switch is to be installed is located near a transformer substation, then a device should be selected that operates at a maximum short circuit of 10 kA. In all other cases, a 6 kA automatic machine is sufficient.
It is worth noting that according to this document, for lighting and socket groups, it is also acceptable to use less powerful switches - by 4.5 kA, although devices of this type are prohibited in Europe.
Step six. Selectivity
This term refers to the shutdown in the event of an unforeseen situation of only a specific area, and not all electricity in the building. Here, the ratings of the machines should be selected in accordance with the serving circuit. So, at the top of the branching, an introductory device is installed with a nominal value corresponding to the maximum permissible load on the circuit (it should be based on the cable section). It is important that the operating current of this machine exceed that of other switches located in the shield below. Below are the main standards:
- for the average country house a 40 amp device is required (as already mentioned);
- for lighting - 10 amperes;
- for an electric stove - 32 amperes;
- for a socket - 16 amperes;
- for electrical appliances with a power of up to 5 kilowatts - by 25 amperes.
This assembly technology will fully satisfy the condition of selectivity.
Step seven. Number of switches
It is also necessary to determine the required number of switching devices. Here are the basic requirements:
- one input switch must be on the shield;
- one - on the lighting line;
- one - on the outlet line;
- one for each powerful appliance (water heater, etc.).
In this case, you can be sure that no overvoltage will occur.
Video - Features of choosing a switching device
Marking
When choosing a machine, you should also study the symbols on the front. It briefly summarizes the main characteristics of the model, the main of which is the maximum allowable operating current.
All models are conditionally divided into three categories, denoted by the letters B, C and D.
- Letter AT indicates that the device will trip within five seconds after the load current exceeds three times the allowable value.
- Group Models FROM are triggered in two seconds after a fivefold excess.
- Finally, switches marked with the letter D, are triggered in one to two seconds after a tenfold excess of the load.
Video - How the circuit breaker works
Common mistakes when choosing a machine
The following mistakes are often made by novice electricians. In order to avoid a “miss” with the face value, it is recommended that you familiarize yourself with these errors.
- First of all, you should focus not on the power of electrical equipment, but on wiring. If the latter is already old, then you need to be especially careful. For example, an outlet requires a 16 amp device, while an old aluminum wire can withstand only 10 amps and will quickly melt after installing such a powerful model. In such cases, there is nothing left but to replace the wiring.
- Ideally, all purchased automation should be from the same manufacturer. Here the probability of inconsistency will be minimal.
- If an average indicator was obtained during the calculation (for example, 13.9 amperes, that is, neither 16 nor 10), then it is better to give preference to a higher indicator, but only on condition that the wiring is able to withstand 16 amperes.
- For summer cottages, it is recommended to install machines of greater power than required according to the calculations. The fact is that such powerful devices as a welding machine, an asynchronous motor, a submersible pump, etc. can be used here. As already noted, 40 amperes is enough for domestic use.
And the last thing: circuit breakers are designed for one or another number of operations, depending on the manufacturer and product quality. Therefore, before buying, you should find out this indicator.
