Electric cables are made of a conductive metal, typically copper, drawn into thin wires that are grouped together to form a single compact conductor.

This single conductor is called a core. Depending on the number of cores present, the cable is classified as unipolar, bipolar, tripolar, quadrupolar, and so on.

Each core must be covered with an insulating protective sheath, usually made of a plastic material such as PVC, which ensures safety and protection from direct contact.

There are also special cables designed for specific applications, such as high-temperature resistant cables featuring insulation made of high-performance silicone material.

When talking about tripolar cables (generally made up of Phase, Neutral and Earth), the key measurement is the cross-sectional area of the internal conductors, expressed in square millimetres (mm²).

Here is a summary table of the standard sizes most commonly used in residential and light industrial installations.

In a standard tripolar cable compliant with the CEI UNEL 00722 standard, the colours of the internal conductors are mandatory:

1. Blue: Neutral.
2. Yellow-Green: Earth (protective conductor).
3. Brown (or Black/Grey): Phase (Live).

To identify the correct cable cross-section, three key factors must be considered:

• The load (Watts/Amperes): The higher the power demand, the larger the cable cross-section must be to avoid dangerous overheating.
• The cable length: For runs longer than 20-30 metres, it is advisable to use the next size up to compensate for voltage drop.
• The installation method: A cable embedded in a wall dissipates less heat than one laid in open air, thus reducing its effective current-carrying capacity.

Practical example: For a standard 16A domestic socket, the minimum required by Italian regulations is a 2.5 mm² cable. For lighting circuits, a 1.5 mm² cable is sufficient.