Protection devices
Overcurrent and residual-current protection are at the core of AREI safety. Here you’ll see what breakers, RCDs, and RCBOs do.
In residential installations you mainly encounter these families:
- Overcurrent protection (breaker/fuse) against overload and short-circuit
- Residual-current protection (RCD/RCBO) against leakage to earth
Protection against overload and short-circuit
In the official AREI terminology, this function is called overcurrent protection. In plain language, it protects cables and connected equipment against:
- overload (too high current causing overheating),
- short-circuit (very high fault current).
In the app this shows up in checks like *breaker vs cable cross-section* and *cascade protection*.
Breaker / MCB
A breaker (MCB) or a fuse has a rated current and a tripping curve. Its job is to ensure the cable does not get more current than it can safely carry.
Key ideas:
- In practice it’s about the combination cable cross-section ↔ breaker rating
- The curve (B/C/D), also called the tripping characteristic, describes when the breaker’s fast magnetic trip reacts.
What do B, C and D mean?
The letter indicates how much short-duration inrush current the breaker allows before its fast magnetic protection trips:
| Characteristic | Practical meaning |
|---|---|
| B | Reacts most readily to a short high-current peak. |
| C | Allows a higher inrush current, for example from some motors, transformers or power supplies. |
| D | Allows an even higher inrush current and therefore needs careful design checks. |
A C characteristic is not generally required in a home. A C16 breaker is still a 16 A breaker and must still protect the cable against overload. The difference is that a higher fault current is needed for the fast magnetic trip. That is why, at the same short-circuit current, a C breaker can trip later than a B breaker.
The choice between B, C and D depends on the load, the wiring and the prospective short-circuit current. Automatic disconnection must still happen within the required time. Do not choose C just because it sounds “stronger”: an installer must also check the loop impedance, short-circuit capacity and the manufacturer’s data.
Short answer
For ordinary lighting and socket circuits, C is not automatically better or mandatory. B is often suitable for normal loads; C is used when a higher inrush current would otherwise cause nuisance tripping.
Residual Current Device (RCD)
An RCD measures the difference between outgoing and returning current. If some current “leaks” to earth (for example through a person), the RCD trips.
In Belgian residential practice you often see typical 300 mA and 30 mA applications (fire and personal protection).
RCBO (combined breaker + RCD)
An RCBO combines in one device:
- overcurrent protection (breaker-like behavior),
- residual-current protection (RCD-like behavior).
In practice this makes it easier to properly protect one specific circuit without immediately switching off larger parts of your installation.