Calculation of the cable cross-section for current, power, length

To date, there is a wide range of cable products, with a cross-section of cores from 0,35 mm.kv.and higher.

Use of caliper

If you incorrectly select the cable cross section for household wiring, the result can have two totals:

An excessively thick core will "hit" your budget, becauseits linear meter will cost more.
If the conductor diameter is not suitable( less than necessary), the cores will begin to heat up and melt the insulation, which will soon lead to spontaneous combustion of the wiring and short circuit.

As you understand, both of these results are disappointing, therefore, before installing the electrical wiring in the house and apartment, it is necessary to correctly calculate the cross-section of the cable, depending on the power, current strength and length of the line. Now we will take a closer look at each of the techniques.

Contents:

Calculating the power of electrical appliances
Calculating the current load
Calculating the length
Video calculation examples

Calculating the power of electrical appliances

Each cable has a nominal power that it can withstand electrical appliances. If the power of all electrical appliances in the house exceeds the calculated indicator of the conductor, then the accident can not be avoided in the near future.

To independently calculate the power of electrical appliances in the house, it is necessary to write down the characteristics of each device separately( a plate, a TV, lamps, a vacuum cleaner, etc.) on a sheet of paper. After that, all values are summed up, and the finished number is used to select the optimal diameter.

The calculation formula is:

Pobsch =( P1 + P2 + P3 +. .. + Pn) * 0.8,

Where: P1..Pn is the power of each electrical appliance, kW

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

Cable capacity selection tables for power:

The required cross-section of the aluminum conductor by power

For conductor with aluminum conductors

The required cross-section of a copper conductor by power

For conductor with copper conductors

As you can see, for each specific cable type, the tabulated values have their data. All you need is to find the nearest value of power and look at the corresponding cross-section of cores.

So that you can clearly understand how to calculate the cable in terms of power, let's give a simple example:

We calculated that the total power of all electrical appliances in the apartment is 13 kW.This value should be multiplied by a factor of 0.8, which as a result will give 10.4 kW of the actual load. Next, in the table, look for a suitable value in the column. We are satisfied with the figure "10.1" with a single-phase network( voltage 220V) and "10.5", if the network is three-phase. Total, the choice of the cross-section is stopped with a 6-mm conductor with a single-phase network or with a 1.5-millimeter meter with a three-phase network. As you can see, everything is quite simple and even an electrician-beginner to cope with such a task independently!

Calculation of current load

Calculation of the cross-section of the current cable is more accurate, so it is best to use it. The essence is similar, but only in this case it is necessary to determine the current load on the wiring. To begin with, we use the formulas to calculate the current strength for each of the electrical appliances.

Average power of household electrical appliances

Example of displaying the power of an electrical appliance( in this case an LCD TV)

If the house is a single-phase network, use the following formula for calculation:

For a three-phase network, the formula will look like:

Three-phase current calculation formula

Where, P - power of the appliance, kW

cos Fi - power factor

Then all currents are summed up and according to tabular values it is necessary to select the cross section of the current cable.

We draw your attention to the fact that the table values will depend on the conditions of the conductor's laying. When installing an open wiring current loads and power will be much greater than when laying wiring in the pipe.

It should be noted that the total value of currents obtained in the calculation is recommended to be multiplied by one and a half times, for the stock. Suddenly, over time, you decide to purchase more powerful electrical appliances?

Cable current selection table:

Table of the ratio of the diameter of the conductors to the current loads

Length calculation

Well, the last way to calculate cable cross-sections is by length. The essence of the following calculations is that each conductor has its own resistance, which with increasing the length of the line contributes to current losses( the greater the distance, the greater the loss).In the event that the amount of losses exceeds the 5% mark, it is necessary to choose a conductor with veins larger.

For calculations, the following procedure is used:

The total power of electrical appliances and the current must be calculated( we have provided the corresponding formulas above).
The electrical wiring resistance is being calculated. The formula has the following form: conductor specific conductivity( p) * length( in meters).The resulting value must be divided into the selected cable cross-section.

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

We draw your attention to the fact that the current passing length should be multiplied by two times, becausecurrent initially goes through one vein, and then comes back on the other.

Calculate the voltage loss: the current is multiplied by the calculated resistance.
The loss value is determined: the voltage losses are divided by the mains voltage and multiplied by 100%.
The final number is analyzed. If the value is less than 5%, leave the selected section of the core. Otherwise, we select a more "thick" conductor.

Resistivity table:

Table of resistivities of conductors

If you are pulling a line for a rather long distance, be sure to calculate with the loss in length, otherwise there will be a high probability of incorrect cable cross-section selection.