MCBs – Miniature Circuit Breakers for Domestic & Commercial Circuits

What Is an MCB?

An MCB, or miniature circuit breaker, is a protective device that disconnects a circuit automatically if it detects an overload or short circuit. Unlike a fuse, an MCB can usually be reset once the fault has been identified and cleared.

What Do MCBs Protect Against?

MCBs are designed to protect wiring and connected circuits against:

• Overload current – where a circuit is drawing more current than it was designed to carry
• Short circuit faults – where fault current rises sharply and rapid disconnection is needed

Types of MCBs

• Type B MCBs – trip faster and are commonly used on standard domestic circuits. Browse B Curve MCBs.
• Type C MCBs – used where circuits have higher inrush current, such as certain motors or commercial loads. Browse C Curve MCBs.
• Type D MCBs – selected for more specialist applications with very high inrush current.

B Curve vs C Curve MCBs

One of the most common selection questions is whether to use a Type B or Type C MCB. In simple terms, B curve is typically used on standard low-inrush circuits such as lighting and sockets, while C curve is used where connected equipment has a higher start-up current. The correct choice depends on the circuit design and the characteristics of the load.

MCB Sizes & Ratings

MCBs are available in a wide range of current ratings. Common UK sizes include:

• 6A and 10A – often used for lighting circuits
• 16A and 20A – common on radial circuits and dedicated loads
• 32A – often used for ring circuits or heavier standard circuits
• Higher ratings – used on larger or more specialised installations

Single Pole, Double Pole & Three-Phase MCBs

The right MCB is not just about amp rating. Installers also need to choose the correct pole configuration for the board and application. Single-pole devices are common in standard domestic circuits, while other formats are used where different isolation or three-phase arrangements are required.

Where MCBs Are Used

• Domestic consumer units – for lighting, sockets, cookers, and other final circuits
• Commercial distribution boards – where different curve types may be needed
• Three-phase installations – where multi-pole devices are used across larger power systems
• Garage, workshop, and outbuilding boards – where dedicated circuit protection is required

MCBs vs RCBOs

An MCB protects against overload and short circuit faults. An RCBO adds residual current protection as well, combining MCB and RCD functions in one device. If the circuit design requires earth leakage protection at circuit level, an RCBO may be the more suitable option.

FAQs on MCBs

What is an MCB used for?
An MCB is used to protect electrical circuits from overload and short circuit faults by disconnecting power automatically when unsafe current levels are detected.

What size MCB do I need?
The correct size depends on the circuit design, cable size, installation method, and expected load. The breaker must be selected to suit the circuit it is protecting.

What’s the difference between Type B and Type C MCBs?
Type B MCBs trip faster and are generally used on standard low-inrush circuits, while Type C MCBs are used where a circuit has a higher start-up current.

Do MCBs need replacing after they trip?
Usually no. One of the main benefits of an MCB is that it can generally be reset once the fault has been found and corrected.

Why Buy MCBs from Power & Data UK?

Power & Data UK supplies trade-focused circuit protection products with dependable UK stock, practical product choice, and fast dispatch. Orders over £30 qualify for free UK mainland next-day delivery, and products are backed by a 2-year manufacturer warranty. For unwanted items, see our returns policy.

Explore Related Categories

• B Curve MCBs
• C Curve MCBs
• 6kA MCBs
• 10kA MCBs
• RCBOs
• Circuit Protection