Where are 10 A, 16 A, 20 A, 25 A and 32 A circuit breakers used?

Short answer: A 10 A circuit breaker may protect a suitable lighting circuit, while 16 A breakers are used for suitable socket and appliance circuits. Ratings of 20 A and 25 A may suit dedicated circuits with higher current demand, and 32 A breakers may protect appropriately designed high-power appliance circuits or distribution feeders. However, the appliance category alone does not determine the breaker rating. Load current, cable capacity, connection ratings and the manufacturer's instructions must agree.

This guide concerns miniature circuit breakers (MCBs) and uses 230/400 V supply examples. Circuit arrangements and national installation requirements vary. A breaker and a fuse with the same ampere rating are not automatically interchangeable.

Typical applications and power equivalents

The power figures below assume a 230 V single-phase supply and a power factor of 1. They are calculated equivalents of the stated currents, not universal safe or continuous load limits. The applications are examples for properly designed circuits, not appliance-to-breaker selection rules.

There is no universal “25 A for an oven” or “20 A for an air conditioner” rule. Different models within the same appliance category can have different electrical requirements. Check the installation instructions for the exact model and supply arrangement.

How do you convert watts to amperes?

For single-phase AC, active power follows P = U × I × power factor. For a resistive load with a power factor close to 1, this simplifies to I ≈ P / U. Motors and electronic equipment may require additional information; use the specified input current and power factor where available.

Example: Two resistive heaters rated at 2,000 W each draw approximately 4,000 / 230 = 17.4 A together on a 230 V supply. Plugging them into separate wall sockets does not establish that they are on separate circuits. If both sockets share a 16 A circuit, their combined current exceeds its breaker rating. The breaker remaining closed does not prove that the arrangement is suitable.

For calculations at other voltages, see converting watts to amperes at 12 V, 24 V and 230 V.

Why does cable capacity control breaker selection?

One purpose of an MCB is to protect circuit conductors against overcurrent. Increasing the load therefore cannot be addressed simply by increasing the breaker rating. An initial overload coordination check is I_b ≤ I_n ≤ I_z, where I_b is design load current, I_n is breaker rated current and I_z is the cable's allowable current under its actual installation conditions.

Example: A 5,000 W resistive load draws approximately 21.7 A at 230 V. Suppose the installed cable has a corrected current-carrying capacity of 24 A for this example. A 20 A breaker is below the load current, while a 25 A breaker exceeds the cable capacity. Neither selection resolves the mismatch; the load or circuit design needs to be reconsidered.

Cable cross-section alone cannot establish the correct breaker rating. Conductor material, insulation, installation method, ambient temperature and grouping with other cables affect current-carrying capacity. See current-carrying capacity by cable cross-section.

The current relationship above is only part of the design assessment. Voltage drop, fault disconnection times and short-circuit withstand also need verification.

Are B16 and C16 equivalent? Does a 16 A breaker trip immediately above 16 A?

B16 and C16 breakers both have a rated current of 16 A. The letter identifies the instantaneous magnetic tripping characteristic. Choosing C16 does not increase the circuit's continuous current capacity above 16 A. The characteristic must suit both the load's starting current and the installation's fault conditions. Read the difference between type B, C and D circuit breakers.

A 16 A MCB is not a precise current limiter that opens instantly at 16.01 A. Overload tripping time depends on current magnitude, temperature and the device's time–current characteristic. Short-circuit operation is assessed separately. “It has not tripped” is not evidence that a circuit is safely loaded.

Can a 32 A breaker increase the capacity of a 16 A socket?

No. Replacing a breaker does not increase the rating of a socket, plug or extension lead. A connection rated at 16 A must not be assumed capable of carrying 32 A. A higher-power appliance needs a coordinated circuit, including suitable conductors, connections and protection.

Similarly, the total rating of a multi-outlet extension applies to the unit as a whole, not independently to every outlet. Read how many watts a socket can handle alongside why increasing a circuit breaker's current rating can be dangerous.

Does 32 A mean the same power on single-phase and three-phase supplies?

No. At a power factor of 1, 32 A on a 230 V single-phase supply corresponds to approximately 7.36 kW. For a balanced three-phase load at 400 V line-to-line, 32 A per phase corresponds to approximately √3 × 400 × 32 = 22.2 kW in total. A three-phase 32 A breaker does not provide 96 A on one phase.

See the difference between single-phase and three-phase electricity. A calculated operating current does not automatically establish the breaker rating required by the equipment manufacturer.

Do not confuse an RCCB current rating with overload protection

A 40 A marking on an RCCB does not mean that it provides the overload protection of a 40 A MCB. An RCCB without integral overcurrent protection performs a different function. An RCBO combines residual-current and overcurrent protection.

The distinction is explained in the difference between an MCB, an RCD and an RCBO. Suitable earthing and grounding and installation verification are also essential parts of the protection arrangement.