ACB vs MCCB in LV Switchgear: What’s the Difference for Commercial Buildings?

When designing, maintaining, or upgrading low voltage switchgear, one of the most common questions is the difference between ACB and MCCB circuit breakers.

Both are essential protection devices used in electrical distribution systems, but they serve different purposes depending on system size, load, and application.

For facilities managers and engineers working with commercial electrical systems, understanding when to use each type is critical for safety, performance, and compliance.

If your organisation operates complex electrical infrastructure, it is important to ensure your LV switchgear and power distribution systems are designed with the correct protection devices.

What Is an ACB?

An Air Circuit Breaker, or ACB, is a high-capacity circuit breaker used in low voltage systems to protect electrical circuits from overloads and short circuits.

ACBs are typically installed in main switchboards where large amounts of electrical current must be controlled and protected.

Key characteristics of ACBs include:

• High current ratings, often up to several thousand amps

• Adjustable protection settings

• Advanced fault detection capabilities

• Ability to be withdrawn for maintenance

ACBs are commonly used as the main incoming breaker in commercial LV switchgear systems.

What Is an MCCB?

A Moulded Case Circuit Breaker, or MCCB, is a more compact circuit breaker used to protect smaller circuits within electrical distribution systems.

MCCBs are typically installed downstream from the main switchboard to protect individual circuits or equipment.

Key characteristics of MCCBs include:

• Lower current ratings compared to ACBs

• Fixed or adjustable trip settings

• Compact design

• Cost-effective protection for smaller loads

MCCBs are widely used throughout LV switchgear distribution systems to protect outgoing circuits.

Key Differences Between ACB and MCCB

Understanding the differences between ACBs and MCCBs helps ensure the correct device is used for each application.

Current Rating

• ACB: Designed for high current applications, often above 800A

• MCCB: Typically used for lower current circuits

Location in the System

• ACB: Installed at the main incoming supply

• MCCB: Installed on outgoing feeders and sub-circuits

Adjustability

• ACB: Highly adjustable protection settings

• MCCB: Limited or partially adjustable settings

Maintenance

• ACB: Can be withdrawn and serviced

• MCCB: Usually fixed and replaced rather than serviced

Cost 

• ACB: Higher cost due to complexity and capacity

• MCCB: More cost-effective for smaller circuits

ACB vs MCCB Comparison Table

 

Feature	ACB	MCCB
Typical Current Range	High	Medium
Installation Location	Main incomer	Outgoing circuits
Adjustability	High	Limited
Maintenance	Serviceable	Replaceable
Cost	Higher	Lower
Application	Large systems	Smaller circuits

When Should You Use an ACB?

ACBs are used where high current and advanced protection are required.

Typical applications include:

• Main incoming supply in large buildings

• Industrial facilities

• Data centres

• High load commercial environments

They provide central protection for the entire electrical system.

Facilities operating high demand LV switchgear infrastructure rely on ACBs for primary protection.

When Should You Use an MCCB?

MCCBs are used to protect smaller circuits within the electrical system.

Typical applications include:

• Distribution boards

• Sub-circuits

• Individual equipment protection

• Secondary panels

They are ideal for managing risk at a local level within commercial switchgear systems.

Why Choosing the Right Breaker Matters

Selecting the wrong type of breaker can lead to:

• Poor fault protection

• Increased risk of overheating

• Reduced system reliability

• Compliance issues

• Higher long term maintenance costs

Proper system design ensures that ACBs and MCCBs work together to provide layered protection across the entire electrical network.

Organisations should regularly review their LV switchgear and distribution systems to ensure protection devices remain suitable.

How ACB and MCCB Work Together in Switchgear

In most commercial systems, ACBs and MCCBs are not alternatives but complementary components.

A typical setup includes:

• ACB at the main incomer controlling the entire system

• MCCBs protecting individual outgoing circuits

This layered approach ensures faults are isolated at the correct level, preventing widespread disruption.

This structure is standard in well-designed low voltage switchgear systems.

Common Mistakes When Comparing ACB and MCCB

Many people assume ACB and MCCB are interchangeable, but this is not the case.

Common mistakes include:

• Using MCCBs for high load applications

• Over-specifying ACBs where not required

• Ignoring system coordination

• Failing to consider future load growth

Correct selection is essential for both performance and safety.

Frequently Asked Questions

What is the main difference between ACB and MCCB?

The main difference is capacity. ACBs handle high current at the main supply, while MCCBs protect smaller circuits.

Can MCCB replace ACB?

No. MCCBs are not designed for the high current levels typically handled by ACBs.

Where is an ACB used in switchgear?

ACBs are usually installed at the main incoming supply to protect the entire system.

Where are MCCBs used?

MCCBs are used on outgoing circuits and distribution boards.

Which is more expensive, ACB or MCCB?

ACBs are more expensive due to higher capacity and advanced protection features.

Are ACBs serviceable?

Yes. ACBs can be withdrawn and maintained, unlike most MCCBs.

Do MCCBs require maintenance?

MCCBs require inspection but are typically replaced rather than repaired.

Can both be used in the same system?

Yes. Most commercial systems use both ACBs and MCCBs together.

Which is better for commercial buildings?

Both are required. ACBs handle main protection, while MCCBs protect individual circuits.

How do I choose between ACB and MCCB?

Selection depends on load, system design, and application. A proper electrical assessment is recommended.