Cable Cross-Section per Circuit Breaker: Which Cable for Which Breaker?
Cable cross-sections by circuit-breaker rating under AREI 4.4.1.4 and 5.2.1.2 — including the complete Table 4.11 for fuses and circuit breakers.
Cable Cross-Section per Circuit Breaker
The breaker protects the cable, not the appliance. If a cable that is too thin is connected to an oversized circuit breaker, the cable can overheat and cause a fire. The correct matching of cable cross-section and breaker rated current is safety-critical and mandatory under AREI regulations.
Quick Reference: Breaker → Minimum Cross-Section
This overview reads Table 4.11 in the direction the question is asked on site: the breaker is fixed, and you need the smallest permissible copper cross-section.
| Circuit Breaker | Minimum Cable Cross-Section | Typical Application |
|---|---|---|
| 10 A | 1.5 mm² (Table 4.11 permits 1 mm², but Table 5.1 does not allow that size in fixed wiring) | Lighting |
| 16 A | 1.5 mm² under Table 4.11; socket circuits require at least 2.5 mm² under 5.2.1.2 | Lighting, circuits without sockets |
| 20 A | 2.5 mm² as the Table 4.11 ceiling; installation method, environment and voltage drop can require a larger section | Dedicated final circuit |
| 25 A | 4 mm² | Final circuit with a higher load |
| 32 A | 6 mm² | Cooktop, instantaneous water heater |
| 40 A | 6 mm² (AREI minimum per Table 4.11: 6 mm² → max. 40 A breaker); for main supply cables 10 mm² is common practice (reserve, voltage drop) | Main switch, supply cable |
| 63 A | 10 mm² | Sub-distribution board supply |
| 80 A | 16 mm² | Supply cable, main switch |
| 100 A | 25 mm² | Supply cable, main switch |
The Complete Table 4.11
AREI itself states the assignment the other way round: for each conductor cross-section, the largest permissible rating of the protective device — listed separately for fuses and for circuit breakers. For the same cable, the fuse limit therefore always sits one step below the breaker limit.
Table 4.11 — Rating of the protective device 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 measurement circuits only |
| 0.75 mm² | 4 A | 6 A | built-in distribution-board circuits only |
| 1 mm² | 6 A | 10 A | no permitted exception under Table 5.1 |
| 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 three smallest rows stay out of reach in an ordinary domestic installation. AREI 5.2.1.2 prohibits insulated conductors below 2.5 mm² unless they form an integral part of a machine or appliance. Only the exceptions in Table 5.1 are allowed: 1.5 mm² for circuits without socket outlets, 0.75 mm² for circuits built into a distribution board that supply a single socket outlet, and 0.5 mm² for control, monitoring, signalling and measurement circuits. 1 mm² does not appear in Table 5.1 — so the “6 A fuse / 10 A breaker” row leads nowhere for fixed wiring.
Important: Table 4.11 gives the maximum circuit-breaker rating for each conductor cross-section in domestic installations. It does not by itself prove adequate current-carrying capacity under every installation condition. Insulation, cable construction, installation method, ambient temperature and voltage drop still need assessment. The table does not apply to non-domestic installations, where current-carrying capacity is calculated according to the rules of the trade.
AREI Basis
| AREI Article | Rule |
|---|---|
| Art. 4.4.1.4 | Table 4.11: Maximum fuse and circuit-breaker rating per conductor cross-section in domestic installations |
| Art. 5.2.1.2 | Choice of electrical conductors: cross-sections below 2.5 mm² prohibited, exceptions per Table 5.1 (1.5 mm² for circuits without sockets) |
| Table 5.1 | Conductors permitted below 2.5 mm²: 1.5 mm², 0.75 mm² and 0.5 mm², each with a defined field of application |
| Art. 5.2.5 | Voltage variation (voltage drop) in conductors must be limited to the values described in the rules of the trade |
Why Does This Matter?
A cable with too small a cross-section heats up under high load. If the breaker is oversized, it will not trip in time — the cable overheats and there is a fire hazard. The rule is therefore always: The breaker must be less than or equal to the current-carrying capacity of the cable.
Consider Voltage Drop
For long cable runs, such as a distribution board in the basement feeding a garage, voltage drop can become significant. AREI/RGIE 5.2.5 does not itself state a percentage; it refers to the rules of good practice. Preliminary checks commonly use 3% for lighting and 5% for other final circuits. A larger section than the table value can therefore be necessary.
See how length, load and phase interact in voltage drop and cable sizing, or use the free calculator.
Common Failure at Inspection
One of the most common defects found during electrical inspection: breaker too large for the installed cable cross-section. Especially in older installations with 1.5 mm² wiring that was later protected with 20 A breakers.
When replacing old fuses with circuit breakers, it pays to check both columns: 1.5 mm² wiring on a 10 A fuse is permitted, and on a 16 A breaker as well — but a 20 A breaker on that same cable is not.
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