What the marking means
An MCB (miniature circuit breaker) protects the cable of a circuit from overload and short circuit. Its marking (B10, B16, C25…) has two parts:
- The number is the continuous current in amperes the breaker carries without tripping.
- The letter is the trip curve: how fast it reacts to a short current spike.
Common curves
- B trips at 3–5× rated current — lighting and socket circuits in homes.
- C trips at 5–10× — motors and appliances with inrush current.
- D trips at 10–20× — rare in residential panels.
The golden rule
The breaker is chosen for the cable, not for the appliance. A 16 A breaker on a 1.5 mm² cable can let the cable overheat — see cable cross-sections.