Which section of electric cable to choose?

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The choice of the section of the electric cables is framed by the standard NF C 15-100. Its recommendations are strict and depend on the type of circuit and the maximum protection rating in amperes to define it. Other constraints https://www.bma-tech.com/product_detail/index/8686/245 are added: power loss by distance, type of son and standardized colors.

The section of the electric cables: the essential thing to know

The cables http://www.bma-tech.com/product_detail/index/8690/253  or electrical son used to carry current from one point to another. So far, nothing extraordinary. However, depending on several physical elements (such as voltage, power demand , etc.), the section (the surface of the electrically conductive part, expressed in mm²) of the cables varies. To better determine the necessary section, consider the points below.


To facilitate the choice of section, everything has been defined by standard NF C 15-100 , condensed from all the regulatory requirements regarding the electrical installation of a building .

The calculation method

If the installation is not standardized or regulated , there is a way to calculate the necessary section. This generally applies to specific electrical networks, industrial or even for special cases such as an earth connection , the supply of an outbuilding, a workshop, etc.


The type of cable

Depending on the location and use of the cable, even cables do not have the same shape, do not have the same type of insulation , conductive metal , shielding , etc.

To avoid any problem, such as excessive heating of a line , premature wear or insulation failure, and to obtain optimal operation in complete safety, you must respect the appropriate cable section .

How to choose the right cable section

The standard NF C 15-100

As we saw above, the regulations in force for everything concerning electricity is the standard NF C 15-100 . It must be emphasized that what is encompassed by this standard is in fact all that concerns low voltage :

Between 50 and 1000 volts (V) for alternating current ;

Between 120 and 1500 V for direct current .

It can therefore be deduced from this assumption that, in addition to the electrical installation of a dwelling (which operates in single-phase 230 V AC), the regulatory obligations concerning the section of a cable also apply to an installation. industrial or specific (which generally operates in three-phase 400 V AC, or more rarely DC).

Power from the meter

As we will see later in the method of calculation , it is necessary to know that the longer a cable is, the greater the voltage drop (in V) is important.

In a dwelling, the lengths are often insignificant on this physical point. However, it is a length that (for a house for example), can cause a significant drop in voltage: the power from the meter .

Indeed, your meter (single-phase or three-phase) may be in the street or at the end of an alley. In this case, the voltage drop can be significant and cause malfunctions in your installation . Here is a table that summarizes, depending on the size of your breaker head after meter , the sections to respect according to the cable length.

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