Why cross-section matters
A cable is a resistor: too much current makes it heat up. The insulation ages, melts and can eventually start a fire. The cross-section (mm²) sets how much current a cable can carry continuously.
Typical copper pairs
- 1.5 mm² → B10 — lighting circuits.
- 2.5 mm² → B16 — socket circuits.
- 4 mm² → C20–C25 — ovens, water heaters.
- 6 mm² → C32 — stoves, EV chargers.
- 10 mm² and up — supply feeds and sub-panels.
Breaker and cable are a pair
The breaker must always trip before the cable overheats. That is why our rule engine flags any circuit where the breaker rating is too high for the cable — one of the most common and most dangerous DIY mistakes.