Today there is a wide range of cable products , with a cross-section of conductors from 0.35 mm. And higher.

If you choose the wrong cable cross-section for household wiring, the result can have two consequences:

1. Too thick core will “hit” your budget, as a running meter will cost more.
2. With an inappropriate conductor diameter (smaller than necessary), the cores will begin to heat up and melt the insulation, which will soon lead to self-ignition and short-circuiting of the wires.

As you know, both of these results are disappointing, therefore, before installing electrical wiring in the house and apartment must correctly calculate the cable cross-section depending on the power, current and line length. Now we will consider in detail each method.

Calculating the power of electrical appliances

Each cable has a certain amount of current (power) that it can handle while operating electrical appliances. If the current (power) consumed by all devices exceeds the permissible value of the conductive core, an accident will soon be unavoidable.

In order to independently calculate the power of electrical appliances in the house, it is necessary to separately write down the characteristics of each device on a piece of paper (stove, TV, lamps, vacuum cleaner, etc.). Next, all the values ​​are summed, and the final number is used to select a cable with conductors of ideal cross-sectional area.

The calculation formula is:

Ptot = (P1 + P2 + P3 + … + Pn) * 0.8 ،

Where: P1..Pn – power of each device, kilowatts

We draw your attention to the fact that the resulting number must be multiplied by a correction factor – 0.8. This factor means that only 80% of all electrical appliances will work simultaneously. Such a calculation is more reasonable, because, for example, you will definitely not use a vacuum cleaner or hair dryer for a long time without interruption.

Tables for selecting cable cross-section for power:

These are simple, simplified tables; You can find more exact values ​​in PUE p.1.3.10-1.3.11.

As you can see, the tabulated values ​​​​have their own data for each specific type of cable. All you need is to find the nearest power value and see the corresponding base section.

In order to clearly understand how to correctly calculate the cable by power, we give a simple example:

We calculated that the total power of all electrical appliances in the apartment is 13 kW. This value must be multiplied by a factor of 0.8, which will result in 10.4 kW of actual load. Next, in the table, we look for the appropriate value in the column. We are satisfied with the figure “10.1” for a single-phase network (voltage 220 V) and “10.5” if the network is three-phase.

This means that you need to choose a cross-section of cable conductors that will power all computing devices – in an apartment, room or other room. That is, such a calculation must be performed for each outlet group, powered by a single cable, or for each device, if it is powered directly from the shield.In the example above, we gave a calculation of the cross-sectional area of ​​\u200b\u200bthe input cable wires for the entire house or apartment.

Total, we choose the cross section on a 6 mm conductor with a single-phase network or 1.5 mm with a three-phase network. As you can see, everything is very simple and even a novice electrician will cope with this task on his own!

Calculate the load current

Calculating the cable cross-section for current is more accurate, so it is better to use it. The essence is similar, but only in this case it is necessary to determine the current load on the wires. First of all, according to the formulas, we consider the current strength of each device.

If the house has a single-phase network, then for calculation it is necessary to use the following formula: For a three-phase network, the formula will look like this: where, P – power of the device, kW

Power Factor

Further, all currents are summed up, and according to the table values ​​it is necessary to determine the cable cross-section for the current.

We draw your attention to the fact that the values ​​​​of the tabular values ​​​​will depend on the conditions of laying the conductor. In an open wiring installation the loads and permissible current strength will be much greater than that of pipe wires.

We repeat, no calculation is performed for the cross-section of a particular device or their group.

Table of cable selection for current and power:

Calculation of cable cross-section with current, power, length

Length calculation

Well, the last method that allows you to calculate the cable cross-section – along the length. The essence of the following calculations is that each conductor has its own resistance, which, with increasing line length, contributes to voltage loss (the greater the distance, the greater the loss). In case the value of losses exceeds the 5% mark, it is necessary to choose a connector with larger conductors.

For calculations, the following methodology is used:

• It is necessary to calculate the total power of electrical appliances and the current strength (above we gave the appropriate formulas).
• Calculate wire resistance. The formula is as follows: specific resistance of conductor (p) * length (in metres). The resulting value must be divided by the selected cable cross-section.

R = (p * L) / S, where p is the tabular value

We draw your attention to the fact that the length of the current section must be doubled, because the current flows initially through one core, and then returns through another core.

• The voltage loss is calculated: the current is multiplied by the calculated resistance.

u _losses = i _load * r _wires

Loss = (U _losses / u _name )*100%

• The amount of losses is determined: the voltage losses are divided by the voltage in the network and multiplied by 100%.
• The total number is analyzed. If the value is less than 5%, we leave the primary section selected. Otherwise, we choose a “thicker” connector.

Suppose we calculate that the resistance of our wire is 0.5 ohms, and the current is 16 amps, then:

u _losses = 16 * 0.5 = 8 volts

Loss = (8/220) * 100% = 0.03636 * 100% = 3.6%

Resistance table:

If you extend the line over a fairly long distance, be sure to make a calculation taking into account the losses along the length, otherwise there will be a high probability of incorrect selection of the cable section.