Type B vs type C circuit breakers: which curve and which rating?
The Journal · Oct 19, 2026
Type B vs type C circuit breakers: which curve and which rating?
Written by Engin Demirel · Electrical technician, master instructor · 12 years of experience
Short answer: The letter on a miniature circuit breaker (B, C, D) tells you at what current it trips instantly on a short circuit. Type B trips instantly at 3–5 times its rated current, type C at 5–10 times and type D at 10–20 times. Under overload (too much current for a long time) all three behave the same. In homes and LED lighting, type C is used most often because LED drivers draw a high current at switch-on; type B is preferred where the circuit is long and the short-circuit current stays low. The amp rating is chosen by the cable size, not by the letter: for example 10 A on 1.5 mm² and 16 A on 2.5 mm² circuits.
What does "C16" on the label mean?
- Letter (C): the tripping curve, i.e. the current range where instantaneous (magnetic) tripping starts.
- Number (16): the rated current. The breaker carries this current continuously; above it the thermal part trips over time.
- 4500 or 4.5 kA: breaking capacity, the largest short-circuit current the breaker can safely interrupt.
- 1P, 1P+N, 3P: number of poles. Single-phase circuits use one pole (live) or live + neutral, three-phase circuits three poles.
How a breaker trips: two parts
- Thermal part: under an overload slightly above the rated current it heats up slowly and trips. The higher the current, the faster it trips. This part is the same for B, C and D.
- Magnetic part: trips in a tiny fraction of a second at very high currents such as a short circuit. B, C and D differ in the current at which this part operates.
Example: for a 16 A breaker, instantaneous tripping starts at about 48–80 A for type B and 80–160 A for type C (EN 60898-1).
When to use type C
- LED lighting circuits: LED drivers draw a very short but high inrush current at switch-on. With many fixtures on one circuit, a type B breaker may trip for no apparent reason when the lights are switched on.
- Motor loads: compressors, pumps, washing machines and air conditioners with high starting currents.
- Transformer loads and groups of drivers.
When to use type B
- Long circuits: as the cable gets longer, its resistance rises and the short-circuit current at the far end gets smaller. If that current does not reach the instantaneous threshold of a type C breaker, it trips only on its thermal part, late. On long runs to a garden, outbuilding or remote store, type B trips faster and more safely on a short circuit.
- Simple loads with low inrush: heaters and small appliances on socket circuits.
Type D is for industrial loads with very high starting currents such as transformers, welders and large motors; it is not used in homes.
How to choose the amp rating
A breaker protects the cable, not the appliance. So the cable size and installation method come first, and the breaker must not be larger than the current the cable can safely carry. Typical pairings in homes:
- Lighting: 10 A – 1.5 mm²
- Sockets: 16 A – 2.5 mm²
- Dedicated circuits (oven, air conditioner, water heater): 16–20 A, 2.5–4 mm² depending on the appliance label
On long runs the cable size grows because of voltage drop; the breaker is still chosen by the cable. Replacing a breaker that keeps tripping with a larger one overheats the cable and creates a fire risk. The right fix is to split the load or run a new circuit.
Breaking capacity: is 4.5 kA enough?
The breaking capacity must exceed the highest short-circuit current possible at the breaker's location. In most homes away from the distribution transformer 4.5 kA is enough; buildings very close to a transformer and commercial premises may need 6 kA or 10 kA. The electrical designer makes the call.
Legrand XS4 series
The Legrand XS4 single-phase and three-phase circuit breakers on our site come from 6 A to 63 A with curve B and C options and a breaking capacity of 4.5 kA to EN/IEC 60898-1. You can choose the curve and rating on the product page. We sell and deliver within Turkey.
Together with an RCD
A circuit breaker protects against overcurrent and short circuits; it does not protect people against electric shock. That requires a 30 mA residual current device. The two do not replace each other and are used together in the consumer unit.
- → Circuit breakers
- → Home circuit breakers and fuse box
- → Cable size calculation
- → RCD types A, B, F
- → Single-phase vs three-phase
- → Residual current devices
Frequently asked questions
What is the difference between type B and type C breakers?
The current at which they trip instantly on a short circuit: type B at 3–5 times the rated current, type C at 5–10 times. Their overload behaviour is the same.
Should I use type B or type C at home?
Type C is most common in homes, especially on LED lighting and motor circuits. On very long circuits type B may be preferred so that it trips quickly on a short circuit.
What cable size goes with a 16 A breaker?
In homes a 16 A breaker is usually paired with 2.5 mm² cable. Circuit length and installation method can increase the size; the breaker is always chosen to suit the cable.
Can I fit a bigger breaker if it keeps tripping?
No. The breaker protects the cable; a larger one lets the cable overheat and creates a fire risk. Split the load or run a new circuit of the right size.
What is the difference between 4.5 kA and 6 kA breakers?
The largest short-circuit current they can interrupt. 4.5 kA is enough in most homes; buildings near a transformer and commercial premises may need 6 kA or more.