Type B or Type C circuit breaker: which one should you use?

In homes the standard is a Type B breaker: it trips on a short circuit at about 3 to 5 times its rated current, which clears faults reliably on long domestic circuits. Type C trips at 5 to 10 times rated current and is used where switch-on inrush is high: motors, pumps, large power supplies, many LED drivers on one circuit.

Type B vs Type C circuit breaker (MCB): which one to choose

For 230/400 V installations to IEC standards (Europe, UK and most of the world). North America uses different voltages, colours and rules: see the “Around the world” notes.

Diagram: Type B trips at 3 to 5 times rated current, Type C at 5 to 10 times — The letter is about the magnetic (short circuit) trip, not the overload trip.

What the letter means

A miniature circuit breaker (MCB) has two trips. The thermal trip handles overload and works the same for B, C and D. The magnetic trip handles short circuits, and the letter tells you at what multiple of rated current (In) it acts instantly (IEC 60898-1):

Curve	Instant trip at	Typical use
B	3 to 5 × In	sockets, lighting, general domestic circuits
C	5 to 10 × In	motors, pumps, large power supplies, workshops, long LED runs
D	10 to 20 × In	transformers, very high inrush; rare in homes

On overload, a breaker does not trip at 1.13 × In for at least an hour, and trips within an hour at 1.45 × In. That is why a slightly overloaded circuit can run for minutes before the breaker drops.

Why homes use B

At the far end of a long domestic circuit the short circuit current can be fairly low. A Type C breaker might not reach its instant trip fast enough there. Type B gets there more reliably, which is why it is the safer default.

When C makes sense

B trips the moment you switch something on: many LED fittings, a big power supply, an air conditioner, a pump. That is inrush current, not a fault. A C breaker on that specific circuit is the usual answer.
Motor circuits such as a circulation pump, compressor or gate motor.

Around the world:
• UK and Europe: the same B, C and D curves (BS EN 60898 / IEC 60898).
• USA: breakers follow UL 489 and are not sold by B/C letter; trip characteristics are given by the manufacturer's curves instead.

Note: swapping B for C reduces how fast a fault is cleared on a long circuit. The choice has to be confirmed by an earth fault loop impedance measurement, done by a qualified person.