When designing electrical wiring at home, performing its replacement or repair, the main focus is on safety. The safety of property and the life of people depends on correctly performed work. To ensure the protection of the wiring, a circuit breaker is used. In this article, we will tell you how to calculate the number of machines in the dashboard for an apartment and a private house.
Content:
- General information
- Calculation of the rating of circuit breakers
- Calculation of the number of machines
- Conclusion
General information
Circuit breaker has two types of protection:
- Protects wiring from short circuit. As a result, the currents in the line increase sharply, overheating of the conductors occurs with reflow, and if the currents act for a long time, then with ignition. This leads to a fire, loss of material values and a threat to life.
- Protects the line from prolonged exposure to currents above rated (protection against overload). As a result, the wires heat up above the permissible value, more than +65 0WITH. The insulation begins to melt, a short circuit occurs with the ensuing consequences.
The machine is able to provide reliable protection of electrical wiring, equipment, property, and is able to preserve human health and life. But it cannot protect a person from electric shock. To do this, apply RCD.
However, in order for the circuit breaker to reliably protect the line, it is necessary to correctly calculate. The industry produces machines of various designs, single-pole, two-pole, three-pole and four-pole.
The figure shows single-pole, double-pole and three-pole AB.
Calculation of the rating of circuit breakers
When calculating, they are guided by the established load. From these considerations, the selection of the cross-section of the wires and the device that will protect the line is made.
For example, let's perform line calculations for 3 outlets. It is supposed to connect electrical appliances, a 2 kW washing machine, a 1.5 kW microwave oven and a 0.8 kW electric kettle. The total power is 4.3 kW (4300 W).
Using the formula, we calculate the current:
I = P / U,
I = 4300/220 = 19.54A
(This formula is valid for a resistive load and is used when designing the power supply in an apartment.)
Using the reference tables, we select the appropriate wire cross-section. This takes into account the method of installation and the material of the conductor. Choosing wiring with copper wires.
Select the closest value from the table below. We take a larger section of a copper conductor 2.5 mm2. We'll take the values for "laid in a pipe" because hidden wiring is assumed.
The next step is to select an automatic machine that will be installed in the switchboard. According to the reference table, we select the required circuit breaker.
In practice, a 2.5 mm² cable is used for sockets. Although the table indicates that with an open gasket, 1.5 mm² will suit us. This is more than what we calculated above, and is due to the fact that the cable is laid in the wall, and not on the open air, as well as the features of the circuit breakers - they are ways of passing currents for a long time 13% higher nominal. That is, AB at 16A will conduct current for a long time up to 18A, at 25A - up to 28A, etc.
Below is a part of the table, with a number of ratings of the machines produced by the industry:
Choosing a 16A circuit breaker. According to calculations, the device should be installed at 19.54 A. But the industry does not produce such devices, so we choose a value lower than the calculated one. In addition, the sockets are designed for a current of 16A, therefore, machines of a higher rating cannot be installed regardless of their number.
It will reliably protect the wiring from overload and short-circuit currents in an apartment or in a country house. The calculation is carried out in a similar way when replacing the old electrical wiring in the house.
In other cases, when the connection is not made through an outlet, but directly, like an electric stove, for example, a circuit breaker is selected according to the power of the electric stove. In this case, the cable is chosen such that a current of the rated current can flow through it for a long time, taking into account the losses on the line. It is important to note that the permissible continuous current of the cable of the calculated cross-section must be 13% (and more) higher than the rating of the circuit breaker on this line, for the reasons indicated above.
Calculation of the number of machines
How to calculate the machine for one line was discussed above. Let's calculate the circuit breakers for 1 room apartment.
The figure below shows a typical wiring protection scheme for a one-room apartment:
It follows from it that individual protection of the lines that power the end consumers is used:
- Two ABs are installed, which protect the lighting lines in the corridor and the room, and the second ensures that the lighting in the toilet, bathroom and kitchen is turned off in case of an emergency.
- The sockets are protected not only by AB, but also by additional protection for the RCD. It protects a person from accidental touching live parts of the electrical wiring.
- The protection of sockets and a washing machine is similarly built.
- A separate automatic cut-off machine for the electric stove is allocated.
All devices are mounted in an electrical panel. Often it is mounted in the hallway, and an electric meter and an input AB are installed on the site.
More machines are required for a 2-room apartment. As can be seen from the diagram below.
Six automatic devices are mounted in the switchboard, providing disconnection of lines in case of short circuit or overloads:
- one AB protects the lighting line of the corridor and both rooms;
- the second is installed to illuminate the kitchen, toilet and bathroom;
- the line that feeds the boiler is protected separately;
- the next machine protects the sockets in the corridor, room 1, room 2, toilet and kitchen.
Thus, if a malfunction occurs on one of the lines, it can be easily localized and repaired.
Similarly, the calculation of the number of circuit breakers for a 3-room apartment or for 4 rooms is carried out. In this case, an electrical panel should be selected, taking into account the number of modules in the box.
The figure above shows the installation of circuit breakers in the electrical panel of a modern apartment.
An introductory circuit breaker is mounted in front of the circuit breakers. It protects the electrical wiring of the entire house. As a rule, the nominal value of the input machine is indicated in the power supply contract and cannot be changed to a higher nominal value without the appropriate permission (in any case, it is sealed). An upstream circuit breaker must be installed before the meter, i.e. protect not only the electrical wiring of the entire house or apartment, but also the meter.
An example is shown in the figure below:
When designing electrical wiring for a two-story house, it is assumed that shields are installed on each floor. In this case, according to the PUE (chapter 1.2. NS. 1.2. 11) it is recommended to install reserve protective AB and lay the possibility of developing power systems.
However, the number of backup machines or machines in the electrical panel as a whole is not regulated by any document. But when designing, it is recommended to install additional machines in the amount of 10%.
Also, if less than 10 automatic machines are installed in the switchboard, then one additional backup is installed.
Conclusion
It is not difficult to calculate the number of machines for a house or apartment yourself. You should only adhere to certain rules:
- Knowing the load current, the cross-section of the wire is selected in a larger direction, and the machines are selected for a lower current.
- Input AB is calculated limited by the power allocated to your facility.
- The number of machines is calculated according to the number of wiring lines and consumers.
The calculation of the number of circuit breakers must be done carefully. Not only the safety of material values depends on this, but also the life and health of a person. Therefore, it is recommended to entrust the calculation to qualified specialists.
Related materials:
- How to divide electrical wiring into groups in an apartment and a private house
- How to properly distribute the load across the phases
- How many outlets should there be in the bedroom
