Why and how to calculate the cross-section of wires and the power of the machines when replacing wiring

Undeservedly little attention is paid to this issue. In the framework of this article, we will not analyze what are the reasons for this, but simply correct this flagrant injustice. First of all, we will see what the consequences of non-fulfillment of this part of the work can be.

Electric current can be compared with the movement of water in pipes. For a complete analogy, one only has to imagine that water flows at the speed of light. If the device consumes more energy than the wires can pass, then the latter will experience overload (pressure will rise in the pipes), and they will begin to heat up. At first, this is inconspicuous, but over time, the winding of the wires from the temperature difference will become unusable, lose its integrity. Now imagine that a shell burst in two pipes that lie side by side and two streams of water hit each other (remember that they flow at the speed of light and in different directions). Roughly the same thing happens with a short circuit in the wiring. If you take pipes / wires larger than the required diameter / section, then there is clearly a waste of money for their purchase.

Why do the calculation of the power of automatic safety devices. If their power is less than necessary, then they will turn off the power when this is not required. If on the contrary, then you risk getting molten wiring and a fire due to a circuit breaker that has not tripped, or that tripped out of time. There are a number of special formulas that allow you to accurately calculate the current strength that occurs in the circuit at a certain load. For our needs, we can safely say that they are not needed, since all ready-made values can be seen in the corresponding tables.

The cross section of the wires is selected depending on the load that will be connected to them. Exact values are selected individually for each device or their groups. Add their power, add the control 100 watts to each of them for insurance and on the basis of the table you can find out the required wire cross-section.

It is quite obvious from it that for laying the lighting line, a wire with a cross section of 1.5 mm² will be enough (unless, of course, it is planned to turn on more than forty lamps with a power of 100 W at the same time). For household outlets, 2.5 mm² wires will be quite enough (Even if you turn on the vacuum cleaner, iron, computer and audio system at the same time, there should be no overload), although you, of course, may have other plans. Now the kitchen and bathroom. They are powered separately. In addition to the fact that it is much more convenient, think about the fact that if we add a boiler, microwave, kettle and washing machine to the vacuum cleaner, iron and computer, then choosing a machine for all this and requiring it to work correctly is quite problematic.

An ideal option would be to draw such separate lines:

lighting,
household outlets in the apartment,
sockets in the kitchen
line for water heater and washing machine,
oven,
warm floor,
air conditioning.

We look at the cross-section of wires in the table, the length is trite measured on the walls, according to a plan drawn up in advance. When measuring, do not forget to make an adjustment for possible measurement inaccuracies, as well as add a certain amount in reserve. After mounting the socket, 15-20 cm of wire should look out of it. In addition to the convenience of installation at the moment, this will allow in the future to count on a couple of warm words, without quotes, from those who have to change these outlets.

Circuit breakers. Selected by a similar principle. The total power of the group of devices powered from it is calculated. According to the same table, or according to the formula I = P / U known from the school bench, we find the current strength and select the appropriate machine.

There are mainly three types of machines sold:

Normal circuit breaker. Protects the line from short circuit, plus, it can perform the functions of a simple switch.
Protective Shutdown Device (RCD). A more sensitive device that does not respond to a simple increase in current in the circuit, but measures its difference at the input / output, monitors the leakage of current.
Differential automatic machine (Difavtomat). 2-in-1 - RCD and a simple machine in one case. The most reliable, convenient and expensive option.

That's all for wiring selection. Good and quality repair to you.