In many residential buildings built more than 20 years ago, there are problems with electrical wiring as more and more new ones are added household appliances, with high requirements for network quality and other power indicators. One of the problems is the mismatch between the current strength and the cross-section of the wiring. Everyone is familiar with a short circuit or lumbago in a coil.
To avoid this, replacing cables alone is not enough; you need to install circuit breakers to avoid voltage leakage. It will be useful to know how to choose differential machine or a regular circuit breaker (circuit breaker) to your apartment, depending on the load.
Differences between protective devices
It is necessary to distinguish between a device in the form of a difavtomat and a device protective shutdown. At first glance, there is no particular visible difference, but this is not so.
The RCD is used to de-energize the network when the slightest leak in the circuit is detected. For example, if damaged electric cable, in order not to injure a person, the circuit will be turned off.
The difavtomat, in addition to the RCD, is equipped with a built-in automatic type switch. It serves to de-energize the system, preventing short circuit, circuit overloads, in general. In a word, it's two in one.
A conventional circuit breaker (circuit breaker) protects the circuit from overload, but it cannot create a safe environment for humans. Therefore in modern buildings They install either difavtomats, or RCDs and automata together.
Selection of any protective device depends on network characteristics. Primarily from the load connected to it. Therefore, it is important to know how to calculate the power of the machine based on the load.
Pros and cons
The advantage of the difavtomat is its compactness, versatility, 100% protection of the circuit from sudden overloads or other dangers. Well, the main “trump card” is the cost, which is lower than the total cost of the RCD and automatic type switch.
If you take into account a single case, the difference is not very noticeable, but when buying for the whole house, the benefit is significant. However, a lot depends on the brand of the product. Installation takes little time; the difavtomat also fits quite compactly on the rail.
Automats also have their drawbacks. If it fails, you will have to purchase the product as a set, and not separately.
The occurrence of a short circuit will lead to difficulties in finding its cause. With a divided installation, identification is much simpler: the RCD is turned off - leakage, the circuit breaker - short circuit.
Which type of protective device to choose is not an easy question. As many electricians do: if we are talking about a small apartment, then use a difavtomat.
When you are going to install complex structures, it is best to install separate RCD units and automatic type switches in a group. Moreover, each group must have its own separate switch.
What are the criteria for selecting equipment
If you still prefer the automatic machine as a product of modern technology, choose the product carefully. Please read its technical data carefully. When choosing a machine based on load power, pay attention to the following:
- voltage and phases: products are rated single-phase and three-phase, 220V and 360V, respectively. In the first option there is one terminal, in the second there are three for connection. All indicators are indicated in the equipment passport and marked on the outside of the case;
- leakage current: denoted by the Greek symbol “delta” and calculated in milliamps. You can select correctly based on the following data: for the house as a whole - up to 350 mA, for a specific group - 30 mA, points and lighting - 30 mA, single points - 15 mA, boiler - 10 mA;
- equipment class: A – tripping as a result of DC voltage leakage. AC – in case of alternating current leakage;
- protection against a “zero” gust: if such a thing is detected, the system identifies it as a gust and turns off the equipment;
- switch-off time: indicated by the symbol Tn and should not exceed 0.3 seconds.
For domestic needs, the most common are devices marked “C” and a 25A range. Installation of inlet structures requires more powerful ones in the form of C50, 65, 85, 95.
Sockets and other points - C15, 25. Lighting devices - C7, 12, electric stove - C40.
We can say that this is a time characteristic of the maximum short-term current power that the machine can withstand and not work. “C” means that the machine operates when the rated current is 5-10 times higher.
Calculation of indicators
The calculation of power when choosing a machine is carried out as follows. For example, everyone installation work made with an electric cable with a cross-section of 3.0 and a maximum power of 25A.
The total power of the appliances is: microwave oven 1.5 kW, electric kettle 2.1 kW, refrigerator 0.7 kW, TV 0.5 kW. The total power is equal to 4.7 kW or 4.7 * 1000 W.
To make it easier to calculate the power in each circuit, the load is divided into groups. The highest power equipment is connected separately. You should not neglect low-power loads, since the total calculations can result in a significant result.
To calculate, we use the formula: power / voltage. Total 21.3 A. You will need an RCD or difavtomat with a limit consumption of 25A, no more. If the number of consumers is more than two, then the total power should be multiplied by 0.7 to correct the data. With a load of three or more – by 1.0.
Reduction factors for some devices:
- refrigeration equipment from 0.7 to 0.9, depending on the characteristics of the motor;
- lifting devices and elevators 0.7;
- office equipment 0.6;
- fluorescent lamps 0.95;
- incandescent lamps 1.1;
- lamp type DRL 0.95;
- neon gas installations 0,4.
The power reduction is due to the fact that not all devices can be turned on at the same time.
The machine is selected based on the operating current of the load. The rating of the machine should be slightly less than the calculated current value, but it is also possible to select slightly larger values.
Current value when choosing cable cross-section
The correspondence of the current to the cross-section of the cable cores can be checked using the table
Summary characteristics for a single-phase machine:
- power 17A – power indicator up to 3.0 kW – current 1.6 – cross section 2.4;
- 26A – up to 5.0 – 25.0 – 2.6;
- 33A – 5.9 – 32.0 – 4.1;
- 42A – 7.4 – 40.0 – 6.2;
- 51A – 9.2– 48.4 – 9.8;
- 64A – 12.1 – 62.0 – 16.2;
- 81A – 14.4 – 79.0 – 25.4;
- 101A – 18.3 – 97.0 – 35.2;
- 127A – 22.4 – 120.0 – 50.2;
- 165A – 30.0 – 154.0 – 70.1;
- 202A – 35.4 – 185.0 – 79.2;
- 255A – 45.7 – 240.0 – 120.0;
- 310A – 55.4 – 296.0 – 186.2.
You can also use a special graph that determines the rated current of the machine depending on the load power.
The required cable cross-section is selected based on the total power of the current passing through the wire; a formula will help you calculate it; the calculation scheme is as follows:
where current = total power divided by voltage in the circuit. In most cases, electricians use this formula.
A more accurate formula for calculating power is P=I*U*cos φ, where φ is the angle between the vectors of the current passing through the machine and the voltage (do not forget that they can be variable). But since in household devices powered by single-phase network, there is practically no phase shift between current and voltage, then a simplified power formula is used.
If the network is three-phase, then a significant phase shift may be observed. In this case, during calculations the power is reduced, and the resulting current must be divided by 3.
So, for a device with a power of 6.5 kW:
I = 6500/380/0.6=28.5
Electrical appliances are often marked or have a plate attached indicating this parameter and the power value. This allows you to quickly make calculations. In a three-phase network, type D circuit breakers are used for high power loads.
Automatic switch IEK. Thermal current – 32 A
A circuit breaker has several other names among people - circuit breaker, plug, bag, or simply circuit breaker.
What we are talking about is in the picture on the left. This is the most budget model.
This article will talk about technical specifications circuit breakers, what they are, and how to choose them in various cases.
To a first approximation, sufficient for practical work and understanding of processes, the article provides an understanding of the operation of the circuit breaker.
Some deeper parameters are not considered - for example, time-current characteristic, maximum breaking capacity, etc.
I have already written several articles on this topic on the blog, and I will post links along the way.
Circuit breaker functions
From the name it is clear that this switch, which turns off automatically. That is, myself, in certain cases. From the second name - circuit breaker - it is intuitively clear that this is some kind of automatic device, which protects something.
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Now more details. The circuit breaker trips and turns off in two cases - in case of overload by current, and in the case short circuit (short circuit).
Overcurrent occurs due to faulty consumers, or when there are too many consumers. Short circuit is a mode when all the power of the electrical circuit is spent on heating the wires, while the current in this circuit is the maximum possible. More details will follow.
In addition to protection (automatic shutdown), machines can be used to manually turn off the load. That is, like a switch or a regular “advanced” switch with additional options.
More important function(this goes without saying) – terminals for connection. Sometimes, even if the protection function is not particularly needed (and it never hurts), the terminals of the circuit breaker can be very useful. For example, as shown in the article.
Number of poles
Depending on the number of poles, the machines are:
- Single pole(1p, 1p). This is the most common type. It stands in a circuit and protects one wire, one phase. This is shown at the beginning of the article.
- Bipolar(2p, 2p). In this case, these are two single-pole circuit breakers, with a combined switch (handle). As soon as the current through one of the machines exceeds the permissible value, both will turn off. These are mainly used to completely disconnect a single-phase load when both the zero and the phase break. It is the two-pole circuit breakers that are used at the entrance to our apartments.
- Three-pole(3p, 3p). Used for breaking and protection three-phase circuits. Just as in the case of two-pole ones, these are actually three single-pole circuit breakers, with a common on/off handle.
- Four-pole(4p, 4p). They are rare, they are installed mainly at the input of three-phase switchgears (switchgears) to break not only the phases (L1, L2, L3), but also the working zero (N). Attention! Under no circumstances should the protective grounding (PE) wire be broken!
Circuit breaker current
Automatic currents come from the following series:
0,5, 1, 1,6, 2, 3,15, 4, 5, 6 , 8, 10 , 13, 16 , 20, 25 , 32 , 40 , 50, 63.
The denominations most often used in everyday life are highlighted in bold. There are other denominations, but we won’t talk about them now.
This current for the circuit breaker is rated. If it is exceeded, the switch will turn off. True, not immediately, as stated below:
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Time-current characteristics
Obviously, the machine does not always turn off instantly, and sometimes it needs to “think and make a decision”, or give the load a chance to return to normal.
The time-current characteristic shows after what time and at what current the machine will turn off. These characteristics are also called tripping curves or current-time characteristics. Which is more precise, since it depends on the current after what time the machine turns off.
Tripping curves or current-time characteristics
Let me explain these graphs. As I said above, the circuit breaker has two types of protection - thermal (against overcurrent) and electromagnetic (against short circuit). In the graph, the operation of thermal protection is a section that smoothly descends. Electromagnetic – the curve abruptly breaks down.
The thermal one works slowly (for example, if the current exceeds the nominal value twice, the machine will go out in about a minute), and the electromagnetic one works instantly. For graph IN this instant “starts” when the current exceeds the nominal value by 3-5 times, for the category WITH– 6-10 times, for D(not shown because it is not used in everyday life) - 10-20 times.
How it works - you can imagine what will happen if the current exceeds the nominal value by 5 times, and the protection is with the “C” characteristic, as in all houses. The machine will only go off after 1.5-9 seconds, depending on your luck. In 9 seconds the insulation will melt and the wiring will need to be changed. In this case, therefore, short circuit is better than overload.
Selecting a circuit breaker. Basic Rule
You must select a circuit breaker based on the cross-sectional area of the wire that this circuit breaker protects (which is connected after this circuit breaker). And the cross-section of the wire is based on the maximum current (power) of the load.
The algorithm for selecting a circuit breaker is as follows:
- We determine the power and current of the line consumers that will be fed through the machine. The current is calculated using the formula I=P/220, where 220 is the rated voltage, I is the current in amperes, P is the power in watts. For example, for a 2.2 kW heater the current will be 10 A.
- Select the wire according to the table. A cable with a conductor cross section of 1.5 mm² is suitable for our heater. In the worst conditions in a single-phase network, it holds a current of up to 19A.
- We choose a machine so that it is guaranteed to protect our wire from overload. For our case - 13A. If you install a machine with such a rated thermal current, then at a current of 19A (one and a half times higher), the machine will work in about 5-10 minutes, judging by the time-current characteristics.
Is it a lot or a little? Considering that the cable also has thermal inertia and cannot instantly melt, this is normal. But considering that the load cannot just increase its current by one and a half times, and in these minutes a fire can occur - this is a lot.
Therefore, for a current of 10 A, it is better to use a wire with a cross-section of 2.5 mm² (the current with an open installation is 27 A), and a 13 A machine (if it is exceeded by 2 times, it will work in about a minute). This is for those who want to play it safe.
The main rule will be this:
The wire current must be greater than the current of the machine, and the current of the machine must be greater than the load current
Iload< Iавт < Iпров
This refers to maximum currents.
And if there is such a possibility, the rating of the machine should be shifted towards the load current. For example, the maximum load current is 8 Amperes, the maximum wire current is 27A (2.5mm2). The machine should be chosen not for 13 or 16, but for 10 Amperes.
Here is the machine selection table:
Table for selecting a circuit breaker based on cable cross-section
The choice of circuit breaker clearly depends on the cable cross-section. If the current of the machine is selected more than necessary, then the cable may overheat due to the flow of high current. If the machine is selected correctly, then if the current exceeds it will turn off and the cable will not be damaged.
Pay attention to the cable routing methods (installation type). Depending on where the cable is laid, the current of the selected circuit breaker may differ by 2 times!
According to the table, we have the initial cable cross-section, and select a circuit breaker for it. For us, as electricians, the first three columns of the table are most important.
Now - how to choose a circuit breaker if the power of the devices is known?
Table for selecting a circuit breaker based on load power
Table of consumption and current of the circuit breaker according to the power of devices
It can be seen that the manufacturer recommends different time-current characteristics for different electrical appliances. Where the load is purely active ( different types heaters), the characteristics of the machine “B” are recommended. Where there are electric motors - “C”. Well, where powerful engines with difficult starting are used - “D”.
Table of dependence of the current of the circuit breaker (fuse) on the cross-section
And here is how the Germans treat the circuit breaker current depending on the cross-sectional area of the wire.
When designing the electrical network of a new house, to connect new powerful devices, in the process of modernizing the electrical panel, it is necessary to select a circuit breaker for reliable electrical safety.
Some users are careless about this task, and can without hesitation connect any available machine, as long as it works, or when choosing, they are guided by the following criteria: cheaper, so that it won’t cost too much, or more powerful, so that it won’t break the bank again.
Very often, such negligence and ignorance of the basic rules for choosing the rating of a safety device leads to fatal consequences. This article will introduce the basic criteria for protecting electrical wiring from overload and short circuit, in order to the right choice circuit breaker according to the power consumption.
Briefly the principle of operation and purpose of circuit breakers
In the event of a short circuit, the circuit breaker operates almost instantly thanks to the electromagnetic release. At a certain excess of the rated current value, the heating bimetallic plate will turn off the voltage after some time, which can be found out from the current characteristic time graph.
This safety device protects the wiring from short circuits and overcurrents exceeding the calculated value for a given cross-section of the wire, which can heat the conductors to the melting point and ignite the insulation. To prevent this from happening, you need not only to choose the right protective switch that matches the power of the connected devices, but also to check whether the existing network can withstand such loads.
Appearance three pole circuit breaker Wires must match the load
It often happens that in an old house a new electric meter, automatic machines, and RCDs are installed, but the wiring remains old. A lot of household appliances are bought, the power is summed up and an automatic machine is selected for it, which regularly holds the load of all switched on electrical appliances.
Everything seems to be correct, but suddenly the wire insulation begins to emit a characteristic odor and smoke, a flame appears, and the protection does not work. This can happen if the wiring parameters are not designed for such current.
Let's say the cross-section of the old cable core is 1.5mm², with a maximum permissible current limit of 19A. We assume that several electrical appliances were connected to it at the same time, making up a total load of 5 kW, which in current equivalent is approximately 22.7 A; it corresponds to a 25 A circuit breaker.
The wire will heat up, but this machine will remain on all the time until the insulation melts, which will lead to a short circuit, and the fire can already flare up in full swing.
Protect the weakest link in the electrical wiring
Therefore, before choosing a machine according to the load being protected, you need to make sure that the wiring will withstand this load.
According to PUE 3.1.4, the machine must protect the weakest section of the electrical circuit from overloads, or be selected with a rated current corresponding to the currents of the connected electrical installations, which again implies their connection with conductors with the required cross-section.
If you ignore this rule, you should not blame an incorrectly designed machine and curse its manufacturer if a weak link in the electrical wiring causes a fire.
Melted wire insulation Calculation of the machine's nominal value
We assume that the wiring is new, reliable, correctly calculated, and meets all requirements. In this case, the choice of circuit breaker comes down to determining the appropriate rating from a typical range of values, based on the calculated load current, which is calculated by the formula:
where P is the total power of electrical appliances.
This means active load (lighting, electric heating elements, household appliances). This calculation is completely suitable for a home electrical network in an apartment.
Let's say the power calculation is made: P = 7.2 kW. I=P/U=7200/220=32.72 A. Select a suitable 32A machine from a range of values: 1, 2, 3, 6, 10, 16, 20, 25, 32, 40, 63, 80, 100.
This rating is slightly less than the calculated value, but it is practically impossible for all electrical appliances in the apartment to be turned on at the same time. It is also worth considering that in practice, the operation of the machine begins with a value 1.13 times greater than the nominal value, due to its time-current characteristics, that is, 32 * 1.13 = 36.16 A.
To simplify the selection of a circuit breaker, there is a table where the ratings of the circuit breakers correspond to the power of single-phase and three-phase load:
Current circuit breaker selection table The denomination found using the formula in the above example is closest in terms of power value, which is indicated in the red highlighted cell. Also, if you want to calculate the current for a three-phase network when choosing a machine, read the article about
Selection of circuit breakers for electrical installations(electric motors, transformers) with reactive load, as a rule, is not produced by power. The rating and type of current characteristics of the circuit breaker are selected according to the operating and starting current specified in the passport of this device.
The circuit breakers are calculated based on the planned load in electrical network or group circuit of the apartment. Also, the calculation of the machines can be made based on the cross-section of the electrical cable already laid and functioning in the apartment.
I would like to propose the calculation of circuit breakers in an apartment in two versions. Each option is used for different wiring conditions, but both options are subject to the rules, including those specified in the PUE.
Options for calculating circuit breakers
1.Option. Are you planning new wiring. In this case, the calculation of circuit breakers is carried out based on the planned power consumption of the apartment, the entire electrical network of the apartment as a whole, together with an analysis of the cross-section of the conductor cable cores.
2.Option. You already have functioning electrical wiring and you need, for example, to replace outdated machines with new ones.
Let's consider both of these options.
Calculation of circuit breakers for new electrical wiring
Before calculating, let's remember a little about what we need. First of all, to protect against short circuits and circuit overload. What does the circuit breaker protect? Protects electrical wiring and connection devices (sockets and switches) from overheating and fire.
Depending on the purpose of the circuit and its short circuit protection, we... Here we do without calculations. But now we’ll look into the calculation of exceeding the permissible load.
On the one hand, the circuit breaker must have a rated current or the current of the circuit breaker is greater than or equal to current at maximum load in the chain.
For example, your electrical circuit consists of 9 outlets with a planned maximum load of 3150 W. When I talk about maximum load, I mean that the planned devices will be plugged into all sockets.
The current in the circuit will be equal to 14.3 Amperes. Calculation formula from school:
This means that the rated current of the circuit breaker can no longer be less than this current in the circuit. If it is less, then the machine will constantly knock out, and we do not need this.
Let's move on. On the other hand, the rated current of the circuit breaker cannot be unlimitedly large. We remember that the circuit breaker protects the cable from overheating. Therefore, the upper permissible value of the rated current of the circuit breaker must be such that the wires do not heat up, and this value is called permissible cable current, or rather, the permissible current of the conductors.
We find that the rated current of the circuit breaker must be less than or equal to the permissible current for the conductor.
As a result, we get a simple condition:
Where can I get the permissible TPG current?
The easiest and most reasonable way is to take the permissible conductor current (TCC) from Table 1.3.4. in PUE ed. 7.
Table: Maximum permissible current for apartment electrics for wires with PVC (polyvinyl chloride) and rubber insulation with copper conductors.
This table is not complete, but sufficient for residential wiring. Let me remind you that in apartment electrics, you cannot use wires with conductors thinner than 1.5 mm 2 and you cannot use cables with aluminum TPG thinner than 16 mm 2. (PUE, table 7.1.1)
Now the calculation of the circuit breaker for the new electrical wiring
Of course, the above formula does not provide an accurate calculation of the circuit breaker rating. It only shows its boundaries. We will carry out the calculation itself as follows (in quotes I will carry out the calculation for a conditional example of an electrical circuit of 9 outlets of 450 W each):
- We count the current in the circuit at maximum load ( 9×400W=3600W. 3600÷220=16.36 Ampere);
- According to the PUE table 1.3.4 (see above), we focus on the cross-section of the cable cores and select for wiring the cross-section of the cable cores one step larger, but not less than 1.5 mm 2. (according to the table, 1.5 mm is suitable, select 2.5 mm, since 2.0 is not on sale);
- Again, using the table, we look at the permissible current for the selected cable (25A);
- We find that according to the condition, namely (I network ≤I machine ≤I permissible cable current), 16.36 Amperes ≤I machine ≤25 Ampere).
- On sale for DIN rail, there are machines with a rating of 20 Amperes. We install it.
Another example of calculating a circuit breaker:
A circuit breaker must be installed at the input. According to the condition, the calculated network current is 27.5 Amperes. The input cable is copper, brand VVGng, cross-section 3×10.
1. Using the PUE table, we look at the permissible cable current. It is equal to 50 Amperes.
2. This means the rating of the circuit breaker should be:
27.5 A≤I of the machine≤50 Ampere.
Circuit breakers with a rating of 50 Amps are available for sale. First select the machine: VA47-29 D50 2p 4.5 kA. By the way, how is their name structure deciphered?
Calculation of circuit breakers for functioning electrical wiring
Suppose you already have working electrical wiring and you need to install or replace circuit breakers. In this case, we calculate the machines based on the cross-section of the cables (or wires) of the circuit.
There are also two options here.
Option 1. The cross-section of all cables (wires) in the circuit is the same.
Note: the cable cross-section refers to the cross-section of the cable cores themselves. To calculate it, measure the diameter of the core and use a mathematical formula to calculate the cross-sectional area of the core.
In this case, the calculation of the machine repeats the calculation indicated above, only without calculating the maximum load.
Option 2. Electrical circuits use wires (cables) of different sections.
In this version, the calculation is also not complicated. The circuit breaker is selected according to the smallest cable cross-section according to table PUE 1.3.4. given above and the calculation algorithm given above.
For quite some time now, modern homes have stopped using corks. They were replaced by more technological devices - automatic machines, also known as baggers, although some still call them traffic jams, but this is wrong, because the operating principle of a traffic jam and a machine is somewhat different. Since in this article we will consider the selection of an automatic machine, depending on the cable cross-section, there will be no talk about traffic jams.
So, the machine is a device that allows you to open the electrical circuit automatically in two cases:
- line current overload;
- occurrence of a short circuit (SC).
In the first case, overload occurs due to a malfunction of electrical appliances or their large quantity and power density. In the second case, due to a short circuit, electricity is consumed to heat the wires with the maximum possible current for this section. In addition to the above cases of circuit breakage, the machine provides the possibility of manual control. There is a switch on the body of the device that allows you to open the circuit.
The purpose of the circuit breaker is to protect the section of the electrical circuit for which it is installed, as well as timely opening of this section in the event of an overload or short circuit.
Types of slot machines
Classification circuit breakers occurs according to the following parameters:
- number of poles;
- rated and limit currents;
- the type of electromagnetic release used;
- maximum power switching capacity.
Let's look at it in order.
Number of poles
The number of poles is the number of phases that the machine is capable of protecting. Depending on the number of poles, machines can be:
Rated and limiting currents
Everything is simple here - such a current strength at which the machine will open the circuit. At the rated current and even a little more than stated, work will be carried out, but only when the limit current is exceeded by 10–15% will a shutdown occur. This is due to the fact that quite often the starting currents exceed the maximum possible currents for a short period of time, so the machine has a certain reserve of time, after which the circuit will open.
Type of electromagnetic release
This is a part of the machine that allows you to open the circuit in the event of a short circuit, as well as in the event of an increase in current (overload) by a certain number of times. Releases are divided into several categories, let's look at the most popular:
- B - opening when the rated current is exceeded by 3–5 times;
- C - when exceeded by 5–10 times;
- D - when exceeded by 10–20 times.
Maximum power switching capacity. This is the value of the short circuit current (determined in thousands of amperes) at which the machine will remain operational after the circuit opens due to a short circuit.
Selection of the optimal cable cross-section
Each cable, like a machine, has a certain permitted load current. Depending on the cross-section and material of the cable, the load current also varies. To select a machine according to cable cross-section, use the table.
It should be noted that it is permissible to choose a cable with a small margin, but not a packet switch! The machine must match the planned load! In accordance with the rules for electrical installations 3.1.4, the setting currents of the circuit breakers should be selected those that will be less than the calculated currents of the selected zones.
Let's look at an example: in a certain area, the electrical wiring is laid with a cable with a cross-section of 2.5 mm square, and the load is 12 kW, in this case, when installing a machine (at a minimum current) of 50 A, the wiring will ignite, since a wire with this cross-section is designed for an allowed current of 27 A, and much more passes through it. In this case, the circuit does not break, since the machine is adapted to these currents, but the wire is not, the automation will turn off the machine only in the event of a short circuit.
Neglecting this rule may result in serious consequences!
Important! First, you should calculate the power of the consumers, and then select a conductor of the appropriate cross-section, and only after that select an automatic machine (packet). The rated current of the packet must be less than the maximum current allowed for the wire of this cross-section.
It is thanks to this principle that the wiring will never overheat and, therefore, no fire will occur.
Calculation of consumer power
Each electrical network in an apartment or house can be divided into sections (rooms). Depending on what devices are planned to be used in a particular area, electrical wiring calculations are made. Typically, the electrical wiring zones for each machine are divided among themselves into each room of the apartment or house. One section of wiring for one room, the second for another, and the third for the kitchen and bathroom. What stands apart in this situation are such powerful consumers as electric stoves, ovens, water heaters, heating boilers. This technique requires a dedicated power line, so in modern homes intended for use with electric stoves, to provide power to the device, a separate circuit breaker is installed.
Calculating the required current for a particular section of wiring is quite simple. To do this, use the formula I=P/U, according to which I is the current strength, P is the power (in watts) of all workers electrical appliances on this line, U is the network voltage (standard - 220 volts). To calculate, you need to add up the power of those electrical appliances that you plan to use on the line, and then divide the resulting sum by 220. From here we get the current strength, according to which you will need to select a cable of a certain cross-section.
As an example, let’s take an area (room) and calculate for it a machine and a cable of the required cross-section. The following will work simultaneously in the room:
- vacuum cleaner (1300 W);
- electric iron (1000 W);
- air conditioning (1300 W);
- computer (300 W).
Let's add these indicators (1300+1000+1300+300 = 3900 W) and divide them by 220 (3900/220 = 17.72). It turns out that the current strength is 17.72, we select for this optimal cross section cable, based on the table, we take a copper cable with a cross-section of 2.5 mm or 4 mm square (be sure to take it with a reserve) and a circuit breaker with a rated protection current of 20 amperes.
It is worth mentioning that you should not choose a circuit breaker with an overestimated rated current, since if the electrical network is overloaded (exceeding the continuous-permissible current for a particular wire), the wiring will start to catch fire. The rating of the machine must correspond to the value of the continuous-permissible current of the conductor or be less.
Experienced electricians repeatedly say that you should not install cables with a small cross-section because they are cheap; you should choose a cable with a reserve to avoid overloading the electrical section and causing a fire in the wiring. But choosing a powerful machine gun is contraindicated!
The wiring is installed once, it is difficult to replace it, but replacing the switch in the event of a significantly increased load is much easier.
At the moment, more and more powerful electrical appliances are appearing, so it’s worth taking care in advance in case you decide to use a more powerful vacuum cleaner or add some additional device to the room.
Nuances
In general, readers should not have any questions regarding the selection of packages according to the cable cross-section, but there are some subtleties that we did not mention above.
- A machine with which type of electromagnetic release to choose
In everyday life, machines of categories “B” and “C” are most often used.
This is due to the fastest possible operation of batch switches when the rated current is exceeded. This is extremely important when using appliances such as electric kettles, toasters and irons. Depending on the type of equipment used, you should choose a specific category; it is advisable to give preference to category “B” switches. - A machine with what maximum switching power should you choose?
It depends on the location of the electricity input from the substation to the apartment; if in close proximity, then you should choose one with a switching capacity of 10,000 amperes, otherwise for city apartments there are enough devices for 5,000–6,000 amperes. You can play it safe and choose the option of 10,000 amperes; ultimately, this indicator only affects whether the machine will be operational after a short circuit. - What type of wire to choose: aluminum or copper
We strongly do not recommend purchasing aluminum conductors. Copper wiring is more durable and can handle higher currents.
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