Cable Cross-Section per Circuit Breaker: Which Cable for Which Breaker?
Overview of correct cable cross-sections per circuit breaker according to AREI Art. 4.4.1.5 and 5.2.1.2 in Belgium.
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.
Reference Table
| Circuit Breaker | Minimum Cable Cross-Section | Typical Application |
|---|---|---|
| 10 A | 1.5 mm² | Lighting |
| 16 A | 1.5 mm² (AREI minimum per Art. 4.4.1.5 Table 4.11); for socket circuits however 2.5 mm² (Art. 5.2.1.2) | Socket outlets |
| 20 A | 2.5 mm² (AREI-compliant, regardless of cable length regarding current-carrying capacity); for long cable runs, voltage drop may require an increase to 4 mm² | Dishwasher, washing machine |
| 32 A | 6 mm² | Cooktop, instantaneous water heater |
| 40 A | 10 mm² | Main switch, supply cable |
Important: 2.5 mm² is generally permissible for 20 A, regardless of length (regarding current-carrying capacity). The 15 m limit concerns voltage drop: for longer runs, 4 mm² may be required to keep the voltage drop below 3%.
AREI Basis
| AREI Article | Rule |
|---|---|
| Art. 4.4.1.5 | Table 4.11: Maximum breaker rated current per conductor cross-section (cable/breaker matching) |
| Art. 5.2.1.2 | Choice of electrical conductors: Minimum cross-section 2.5 mm², exception 1.5 mm² for circuits without sockets |
| Art. 5.2.5 | Voltage variation (voltage drop) in conductors must be limited to the values described in the rules of the trade |
| Art. 5.2.7 | Fire safety: Cables in bundles must be at least class Cca (CPR fire class) |
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 (e.g., from the distribution board in the basement to the garage), voltage drop can become excessive. The AREI refers in Art. 5.2.5 to the "rules of the trade", which provide for a maximum 3% voltage drop for lighting circuits and 5% for other circuits. In such cases, a larger cross-section must be chosen than the minimum table prescribes.
Rule of thumb: Per 10 m cable length at 16 A, the voltage drop increases by approx. 1.1% for 2.5 mm². At 30 m, that is already 3.3% — 4 mm² would be the better choice.
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.
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