Electrical Cable Section (mm²)

Electrical cable cross-section (mm²)

NBR 5410 picks a cable size by checking two things at once. The first is current-carrying capacity (ampacity, which shifts with the installation method B1/B2/A1), and the second is voltage drop, which has to stay at or under 4% at the load. The standard copper sections, PVC-insulated and run in conduit, are 1.5 / 2.5 / 4 / 6 / 10 / 16 / 25 mm². Take a 15 A load wired by method B1: it lands on 2.5 mm². As for the color code, phase conductors are black / red / grey, neutral is light blue, and protective earth is green-yellow or plain green.

Applications

You will meet these sections all over a house: an electric shower wants 6–10 mm², air conditioning sits at 2.5–4 mm², a lighting circuit gets 1.5 mm² and outlets get 2.5 mm². Beyond the home they feed industrial machinery, low-voltage utility branch circuits, and PV DC strings, which use a dedicated solar cable with double insulation that holds up to UV. Whatever the case, derate the ampacity for grouping, ambient temperature and harmonics.

FAQ

Why not always use the largest section? Money and room, mostly. Conduits and terminals are already sized for the section you planned, so going thicker than needed makes the install both pricier and harder to pull off.

What does method B1 mean? It describes conductors run inside a conduit that is buried in masonry. In NBR 5410 Table 36 it is one of the references engineers reach for most often when reading off ampacity.

Aluminum or copper? For homes and small commercial jobs, copper is the default. Aluminum shows up in long feeders and utility lines, where it carries the same current only if you step up one section above copper and prepare the terminals properly.