According to Ohm's law, current (I) is in direct proportion to voltage (U) and in inverse proportion to resistance (R). Power (P) is calculated by multiplying current by voltage. Thus, for a section of the circuit, the following formula is formed, by which the current is calculated: I = P/U.
Taking into account real conditions, one more component is added to this formula and when calculating a single-phase network, the following form is obtained: I = P/(U x cos φ).
A three-phase network is calculated a little differently. For this, the following formula is used: I = P/(1.73 x U x cos φ), in which the voltage U is conventionally 380 volts, cos φ is the power factor by which the active and reactive components of the load resistance are related to each other.
Expert opinion
Viktor Pavlovich Strebizh, lighting and electrical expert
Any questions ask me, I will help!
When choosing expensive models, you should take into account that all other equipment must be of the same level; wiring, switches and sockets, junction boxes, lighting fixtures. If there is something you don’t understand, write to me!
Selecting a machine by rated current
The considered formulas are widely used in calculations of the input circuit breaker. Using one of them - I = P/209 with a load P of 1 kW, the current strength for a single-phase network is 1000 W/209 = 4.78 A. The result can be rounded up to 5 A, since the actual voltage in the network is not always corresponds to 220 V.
The lighting group is calculated separately. As a rule, the power of lighting devices is estimated at 1.5-2 kW, so a separate machine with a rating of 10 A will be sufficient for them.
What kind of lighting do you prefer?
Built-in Chandelier
Powerful household units are connected not only to automatic machines, but also to residual current devices. Part of the total power should be reserved for lighting and sockets installed in the premises. Correctly performed calculations will allow you to install the wiring efficiently and select the desired switch. In this case, the operation of the equipment will be safe and durable.
Main characteristics of slot machines: what to look for
It should be understood that by installing a more powerful AV with wiring that is not designed for such currents, the home master will only make things worse. The fact is that the automatic switch “doesn’t care” what happens to the outlet or equipment. It is designed to protect wires from overheating due to overloads or short circuits. Of course, this is said in exaggerated terms, but this does not change the essence. That is why it is better if the AB value is lower.
10A circuit breakers are most convenient for protecting your home network. When working with lighting groups, they behave very well. If we talk about power lines, then it is better to divide them into rooms. More powerful protective automation is justified only if equipment such as an electric water heating boiler is turned on. Even to connect a washing machine that consumes 2 kW, a 10A circuit breaker is quite enough. In this case, the cable cross-section should not be less than 1 mm2 for copper and 2 mm2 for aluminum. A sufficient socket rating here can be considered 10 A.
Classification of circuit breakers
- single-pole, only one phase is connected to it, used where the electricity consumer is 220 V;
- bipolar, two opposite phases or phase and zero are connected to it. As soon as a problem occurs in one of the phases (exceeding the current value), two circuit breakers are switched off at once. They are not used in everyday life;
- three-pole, used where there is a three-phase power transmission system. For example, when entering a cottage, apartment buildings;
- four-pole, used in switchgears (RU), for breaking 3 phases and zero, not used in everyday life.
The industry produces a wide variety of automatic machines with rated current: 0.5A; 1A; 1.6A; 2A; 3.15A; 4A; 5A; 6A; 10A; 16A; 20A; 25A; 32A; 40A; 50A; 63A. In everyday life, it is mainly used from 6A to 40A.
When purchasing an AV, you need to choose a rating so that it operates until the moment when the current does not exceed the capabilities of the wiring.
Therefore, you need to know what cross-section you need to lay the wire (cable) to the consumer or group of consumers and their power. The nominal value of AB will depend on this.
Expert opinion
Viktor Pavlovich Strebizh, lighting and electrical expert
Any questions ask me, I will help!
Such switches are produced in the form of modules, due to which they can be freely mounted in the required quantity and in the right place. If there is something you don’t understand, write to me!
The most famous manufacturers of automatic machines
Despite the huge range of similar products on Russian shelves, consumers are not loyal to everyone. Some brands are more popular, others less popular. The main trust of buyers was won by the ABB 10A and IEK 10A machines. According to users, the products of these brands have the best price-quality ratio. It is worth noting that experts also share a similar opinion. Let's look at them in more detail.
Selecting AV based on short circuit current
You can purchase AVs with short circuit ratings: 3,000, 4,500, 6,000, 10,000 Amperes. The choice of AV with the required rating depends on the length of the cable or overhead line from the transformer substation (TS) to your house, apartment or cottage.
If the transformer substation is located nearby, then the short-circuit currents are very high, so you need to purchase a circuit breaker with a cutoff of 10,000 A. In the private sector of households, there is a large length of overhead power lines, so you need to use a circuit breaker with a short-circuit current of 4,500 A. In other cases, the average value is 6 000 A.
An electromagnetic release is a part inside the AB that, in the event of a short circuit (SC), opens the electrical circuit. Releases are divided into categories. We will look at the categories that are used most often:
B – the circuit opens when the rated current is exceeded by 3–5 times;
Automatic machine 1p 10A VA47-29 from IEK and its features
If we compare this AB with ABB, the main characteristics are similar. They have the same denominations, the permissible number of operations and the cost - from 90 to 150 rubles. However, IEK 1p 10 A VA47-29 has one very important feature: it is capable of working not only in a vertical position, but also in a horizontal position. Not every circuit breaker can boast of this.
This AB allows you to connect fairly thick wires with a cross-section of up to 25 mm2. The manufacturer guarantees the operability of the equipment for 6,000 operations in emergency mode and 10,000 in mechanical mode. However, this does not mean that they will withstand 6000 short circuits. We are talking here only about overloads.
A little more about AB in the next video.
Protection against power surges in the apartment
In order to prevent power surges and protect wiring from overload, you need to be careful when using extension cords and tees. When an overload occurs in the network, the wiring begins to heat up and a short circuit or fire may occur.
Another important factor is the cross-section of the wiring (to put it simply, its thickness), on which its endurance depends. Therefore, ideally, it is necessary to calculate the load not only on individual sockets, but also on the entire electrical network of the apartment. Then it will be easier to determine the total permissible power of electrical appliances, lamps and chandeliers. Such precautions are especially useful in older homes.
To avoid problems with a lack of sockets, it is necessary to plan their location and number in advance. During major renovations of apartments, the wiring is often completely replaced with a new one with a larger cross-section. In this case, it is permissible to install European sockets, the current strength of which is from 10A to 16A; the total power of electrical appliances, accordingly, can be much greater.
There are some standards according to which there should be at least 2 sockets in each room (1 for every 4 square meters of area), and in the kitchen - 4. But today this number is not enough. In order not to overload the existing sockets, it is better to install additional ones, taking into account the total permissible load on the wiring.
By following simple precautions and maintaining the wiring in your home in good condition, you can protect your home from fire and keep electrical appliances in working order for a long time.
Expert opinion
Viktor Pavlovich Strebizh, lighting and electrical expert
Any questions ask me, I will help!
To more clearly imagine the consequences of a mismatch between the wiring cross-section and the total power of the devices connected to the network, let’s consider this example. If there is something you don’t understand, write to me!
Some tips for choosing protective automation
When choosing an AB, first of all it is worth calculating its denomination, as already mentioned. However, home craftsmen often make another mistake - distribution by lines or groups. Please note that you cannot connect part of the lighting and several sockets to one machine (for example, in rooms). Here is the approximate location of AB along the lines in a 4-room apartment.
- Automatic 10A for the lighting group of the hallway, living room and kitchen.
- The same for 3 rooms and a bathroom.
- Kitchen power line.
- Living room and bedroom sockets.
- Remaining power points.
With such an arrangement, it will be quite convenient to carry out repairs in the event of an emergency in any of the premises. You don’t have to turn off the lighting completely, nor do you have to turn off all the sockets in the apartment, which will allow you to use power tools.
How to calculate the rating of a circuit breaker?
Here I is the value of the rated current, P is the total power of the installations included in the circuit (taking into account all consumers of electricity, including light bulbs), and U is the network voltage.
To simplify the selection of a circuit breaker and save you from the need to use a calculator, we present a table that shows the ratings of the circuit breakers that are included in single-phase and three-phase networks and the corresponding total load power.
Visually about the selection of circuit breakers in the video:
Calculation of the machine based on power 380
To select a circuit breaker based on power (P), you need to calculate the load current using the formula, then, based on the data obtained, select a circuit breaker of a larger value.
Expert opinion
Viktor Pavlovich Strebizh, lighting and electrical expert
Any questions ask me, I will help!
When purchasing an AV, you need to choose a rating so that it operates until the moment when the current does not exceed the capabilities of the wiring. If there is something you don’t understand, write to me!
How to spot a fake when purchasing
When purchasing a 10A machine (like any other), you should pay attention to its appearance. Using it you can instantly determine what is in your hands. It must be remembered that a counterfeit manufacturer will never manufacture automation using expensive parts.
Looking at the side wall of the original product, you can see a small plug made of hard rubber that matches the body. Underneath there is a bimetallic plate, which helps to cut off in case of overheating. It is this node that is not present on counterfeit products. The specified cover will simply be drawn on the body; it will not be possible to open it. Additional signs include an uneven color of the plastic with foreign inclusions or stains and large gaps on the sides of the lever.
A little theory
It is known from the physics course that there is a relationship between electrical power, current strength and voltage in the electrical network. In a simplified form, this relationship is expressed by the following formula for a single-phase network:
W = I x V (1)
where W is the current power in watts (W);
I – current strength in amperes (A);
V – voltage in volts (V).
In this case, we will be interested in the current strength, since the circuit breaker and electrical wiring characteristics are often selected based on this parameter. For convenience, we transform the above formula into the expression:
I = W / V (2)
As an example, let’s calculate the current strength for the load that the energy-intensive consumers mentioned above provide to the power grid. Their total power will be about 6 kW, and at a voltage of 220 V we get the current in the circuit:
I = 6000 W / 220 V = 27.3 A
For a three-phase connection diagram, formula (2) will take the following form:
I = W / 1.73V (3)
This change is caused by the fact that with an equal load and uniform distribution of power across phases, the current in a three-phase network will be three times less. Thus, with the same total power of 6 kW, but at a voltage of 380 V, the current in the circuit will be equal to:
I = 6000 W / (1.73 x 380 V) = 9.1 A
Having received this indicator, you can begin to select a circuit breaker that provides network overload protection.
What is the danger of a cable mismatch with the network load?
Selecting the correct power circuit breaker is a very important task. An incorrectly selected device will not protect the line from a sudden increase in current.
But it is equally important to choose the correct cross-section of the electrical cable. Otherwise, if the total power exceeds the rated value that the conductor can withstand, this will lead to a significant increase in the temperature of the latter. As a result, the insulating layer will begin to melt, which can lead to a fire.
