Cable size and circuit breaker rating

GREI table 4.11

For domestic installations, subsection 4.4.1.4 gives the maximum rated current of the fuse or circuit breaker protecting a wiring system, according to the cross-section of its conductors:

Conductor cross-section	Fuse: at most	Circuit breaker: at most
1.5 mm²	10 A	16 A
2.5 mm²	16 A	20 A
4 mm²	20 A	25 A
6 mm²	32 A	40 A
10 mm²	50 A	63 A
16 mm²	63 A	80 A
25 mm²	80 A	100 A
35 mm²	100 A	125 A

The GREI table starts at 0.5 mm²; the small cross-sections are mainly used for control and signalling circuits.

This is a maximum: the rating may be lower. A cable’s current-carrying capacity also depends on its insulation, its installation method and the ambient temperature: in unfavourable conditions, a larger cross-section is sometimes needed.

The most common cases

• Lighting in 1.5 mm²: circuit breaker of 16 A at most.
• Sockets in 2.5 mm²: circuit breaker of 20 A at most.
• Circuit in 6 mm², for example for a hob: circuit breaker of 40 A at most.

With fuses, the ratings are lower: 10 A in 1.5 mm² and 16 A in 2.5 mm².

Dedicated circuits

Under subsection 5.2.1.2, in domestic installations, every fixed appliance or machine with a power of 2600 W or more is supplied by its own circuit, known as a dedicated circuit. The GREI also requires a dedicated circuit for:

• the washing machine;
• the dishwasher;
• the tumble dryer;
• the electric cooker;
• the electric hob;
• the electric oven.

Fixed electric heating is supplied by one or more dedicated circuits.

The cross-section of these circuits is chosen according to the appliance’s power, then the circuit breaker from table 4.11.