Which section of electric cable to choose?

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 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  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.