FAQ

Cable Cross-Section per Circuit Breaker: Which Cable for Which Protection?

Which cable cross-section for a 16, 20 or 32 A breaker in Belgium? AREI/RGIE Table 4.11, minimum sizes for socket circuits and what else you need to check.

Published on 18 March 2026 Updated on 5 October 2026 7 min

AuthorStephan Behm

In Belgian domestic installations, AREI Table 4.11 sets the largest breaker per copper cross-section: 16 A on 1.5 mm², 20 A on 2.5 mm², 25 A on 4 mm² and 40 A on 6 mm². Socket-outlet circuits always use at least 2.5 mm² under subsection 5.2.1.2. The protective device protects the cable, not the appliance: a breaker that is too large for the cross-section trips too late on overload, and the cable overheats.

Quick reference: breaker → minimum cross-section

This overview reads Table 4.11 the way the question comes up on site: the breaker is given, and you need the smallest permitted copper cross-section.

Circuit breaker	Minimum copper cross-section	Typical use
10 A	1.5 mm² (Table 4.11 lists 1 mm², but Table 5.1 does not allow 1 mm² for new fixed wiring)	Lighting
16 A	1.5 mm²; socket-outlet circuits at least 2.5 mm² under 5.2.1.2	Lighting, circuits without sockets
20 A	2.5 mm²	Socket circuit, appliance circuit
25 A	4 mm²	Final circuit with a higher load
32 A	6 mm²	Hob, instantaneous water heater
40 A	6 mm² (table ceiling)	Final circuit or supply cable
63 A	10 mm²	Supply to a sub-distribution board
80 A	16 mm²	Supply cable, main switch
100 A	25 mm²	Supply cable, main switch

The table is a ceiling for the protective device, not a finished cable calculation. Installation method, grouping, ambient temperature and voltage drop can require a larger cross-section; how to check them follows below.

The complete Table 4.11

The AREI states the relationship the other way round: for each conductor cross-section, the largest permitted rating of the protective device, separately for fuses and circuit breakers (subsection 4.4.1.4, applicable to domestic installations).

Table 4.11 — Protective device rating by conductor cross-section (AREI 4.4.1.4)

Conductor cross-section	Max. fuse	Max. circuit breaker	Use in domestic installations
0.5 mm²	2 A	4 A	control, monitoring, signalling and measuring circuits only
0.75 mm²	4 A	6 A	circuits integrated in distribution boards only
1 mm²	6 A	10 A	existing wiring from before 17 May 1986 only (Part 8)
1.5 mm²	10 A	16 A	circuits without socket outlets
2.5 mm²	16 A	20 A	generally permitted
4 mm²	20 A	25 A	generally permitted
6 mm²	32 A	40 A	generally permitted
10 mm²	50 A	63 A	generally permitted
16 mm²	63 A	80 A	generally permitted
25 mm²	80 A	100 A	generally permitted
35 mm²	100 A	125 A	generally permitted

The two columns are not interchangeable. For the same cable, the fuse limit sits one step below the breaker limit. Replacing a 16 A fuse with a 20 A breaker on 2.5 mm² raises the rated current, so the circuit needs a fresh assessment.

Table 5.1: the exceptions below 2.5 mm²

Subsection 5.2.1.2 prohibits insulated conductors smaller than 2.5 mm² unless they are an integral part of a machine or appliance. Table 5.1 lists the exceptions exhaustively:

Minimum	Only for
1.5 mm²	circuits without socket outlets; only a single socket of up to 2.5 A built into a luminaire is allowed
0.75 mm²	circuits integrated in switchgear and controlgear assemblies that supply a single socket outlet
0.5 mm²	control, monitoring, signalling and measuring circuits

The 1 mm² row in Table 4.11 therefore does not permit new 1 mm² wiring. Table 4.11 sets how large the protective device may be; Table 5.1 decides whether that cross-section may be installed at all.

Existing installations: 1 mm² wiring

For existing parts of domestic installations, section 8.2.2 (point 5, choice of wiring systems) contains a narrowly defined derogation: EMCB and EMCVB wiring of 1 mm² and CTLB and VTLB wiring of 0.75 mm² may remain in service if on-site execution began before 17 May 1986 and the wiring belongs to circuits without socket outlets. Their protective devices must suit the cross-section. This protects existing wiring; it is not a rule for new work. The age of the installation and the actual cable type must be demonstrable at inspection.

What the table does not decide

A complete selection links three currents: the design current of the load I_B, the rated current of the protective device I_n and the current-carrying capacity of the cable I_Z. As a rule, I_B ≤ I_n ≤ I_Z. I_Z is not a fixed value per mm²: subsection 4.4.1.4 makes it depend on cross-section, insulation, cable construction, installation method and ambient temperature.

So also check:

Cable: material, insulation and construction; the table values apply to copper.
Installation method: in conduit, in thermal insulation, on the wall, bundled or on a cable tray.
Grouping: the number of simultaneously loaded conductors and neighbouring circuits.
Environment: ambient temperature and heat dissipation.
Length and load: voltage drop over the actual cable length.
Short circuit: disconnection conditions, fault-loop impedance and the breaker's breaking capacity against the prospective short-circuit current.

A long run may need a larger cross-section because of voltage drop, and an unfavourable installation method lowers the current-carrying capacity. For non-domestic installations, Table 4.11 is not a blanket ceiling; there you determine I_Z according to the rules of good practice.

Voltage drop: 3% and 5% are guide values, not an AREI limit

Section 5.2.5 ("Voltage drop") requires voltage drop to be limited to the values described in the rules of good practice. Subsection 5.2.1.2 b adds that it must be compatible with safe operation of the connected equipment. The AREI sets no percentage. In practice, designers work with 3% for lighting and 5% for other final circuits: proven guide values for a first check. For long runs, motors, EV charging points or sensitive equipment, calculate with the actual conditions.

The calculation needs cable length, conductor material, cross-section, current, power factor and the supply (single- or three-phase). The guide Voltage drop and cable sizing shows how they interact. For a quick answer, use the free cable sizing calculator.

Replacing an old fuse with a circuit breaker

A classic inspection finding is a protective device that is too large for the installed cross-section. Typical case: in an older installation, fuses were later replaced by breakers and nobody checked the cable behind them.

How to approach it:

Identify the cable: which cross-section and cable type are actually installed, and how?
Classify the existing wiring: does a Part 8 derogation apply, for example to 1 mm² wiring from before 17 May 1986?
Pick the column: for 1.5 mm², Table 4.11 allows at most a 10 A fuse or a 16 A breaker; for 2.5 mm², at most 16 A or 20 A.
Check the circuit type: a socket-outlet circuit needs at least 2.5 mm², regardless of the breaker.

A 20 A breaker on 1.5 mm² is never permitted. The table ceiling is not an invitation to raise the protection either.

AREI basis at a glance

AREI reference	Rule
Subsection 4.4.1.4	Current-carrying capacity `I_Z`; Table 4.11 with the maximum fuse and breaker rating per cross-section
Subsection 5.2.1.2	Choice of wiring: `I_Z ≥ I_B`, compatible voltage drop, in principle at least 2.5 mm²
Table 5.1	Exhaustive exceptions below 2.5 mm²: 1.5 mm², 0.75 mm² and 0.5 mm² for defined uses
Section 5.2.5	Voltage drop limited to the values described in the rules of good practice
Section 8.2.2, point 5	Existing before 17 May 1986: EMCB/EMCVB 1 mm² and CTLB/VTLB 0.75 mm² in circuits without sockets

Checking cross-section and protection in PlanElec

In PlanElec, you record the protective device, cross-section and length for every circuit directly in the single-line diagram. The self-check verifies that the cross-section matches the rated current of the protection and calculates voltage drop from the cable length against the 3% and 5% guide values. The exact rule coverage is listed in What the self-check verifies. Installation method, grouping and on-site measurements are assessed by the electrician; the official inspection is carried out by the accredited inspection body.

Check your cable choice right away

Run load, length, supply network and protection through the cable calculator, then carry the circuit into your PlanElec project.

Open the cable calculator View the example dossier (PDF)

Fictitious sample dossier, available without sign-up.

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