In low-voltage power distribution systems, choosing the right main switch directly determines the safety, reliability, and long-term stability of the entire system. Among all options, the MCCB (Molded Case Circuit Breaker) has become the preferred main breaker for distribution boxes due to its high breaking capacity, advanced protection features, and strong adaptability.

This guide explains the five major advantages of using an MCCB as the main switch, and provides practical installation tips and model-selection guidance to help electrical engineers, contractors, and facility managers make the best decision.

What Is an MCCB and Why Is It Suitable as a Main Switch?

An MCCB is a protective device designed for overload, short-circuit, and isolation functions.
Compared with MCB (miniature circuit breaker) and isolating switches, the MCCB provides higher breaking capacity, adjustable trip settings, and modular expansion—making it ideal for use at the incomer of a distribution box.

5 Key Advantages of Using an MCCB as the Main Switch

High Breaking Capacity for Superior Protection (35kA–100kA+)

An MCCB is engineered to safely interrupt extremely high fault currents, preventing equipment damage and electrical fires.
Typical breaking capacity (Icu) ranges from:

• 35kA

• 50kA

• 100kA or higher depending on model

Why this matters:
In many distribution boxes—especially those close to the transformer—the fault current may exceed what an MCB can handle (usually only 6kA–25kA). Only an MCCB ensures system-level safety.

Compared to other devices:

• MCB: low breaking capacity; not suitable for main incoming circuits

• Isolator: cannot break short-circuit current at all

Integrated Multi-Stage Protection (Overload + Short-Circuit + Instant Trip)

An MCCB combines three protection functions in a single device:

• Long-time delay (overload)

• Short-time delay (short-circuit)

• Instantaneous trip (severe fault)

This ensures selective coordination and prevents unnecessary upstream tripping.

Compared to MCBs:

• Fixed characteristics, no adjustment

• Lower precision

• Harder to achieve selective protection

Compared to isolators:

• No protective function at all

Wide Current Range and Adjustable Settings (16A–1600A)

MCCBs offer various frame sizes and adjustable rated currents, making them suitable for small distribution boards, industrial equipment, and large power systems.

Adjustable parameters include:

• Current setting (Ir)

• Short-circuit trip settings

• Time delay adjustments

This flexibility makes MCCBs ideal for loads with varying power or systems requiring future expansion.

Long Mechanical Life and High Reliability

A high-quality MCCB typically provides:

• Electrical life：several thousand on-load operations

• Mechanical life：tens of thousands of off-load switch operations

• Strong resistance to harsh environments and frequent switching

Why this matters:
The main switch in a distribution box is frequently used during maintenance and shutdown—MCCBs are designed to handle this without degradation.

Excellent Expandability and Remote-Control Capability

MCCBs support a wide range of accessories to enhance automation and management:

Available modules include:

• Auxiliary contacts

• Alarm contacts

• Under-voltage release

• Shunt trip

• Motorized/remote operation mechanism

• Front/rear mounting & wiring options

Application value:

• Enables remote monitoring

• Fits different cabinet types

• Supports smart distribution systems

These capabilities far exceed those of an MCB or isolator.

Where MCCBs Are Best Used as the Main Switch

MCCBs are ideal for scenarios requiring high breaking capacity, adjustable protection, or remote control:

• Main power supply of a distribution box or cabinet

• Large electrical equipment such as pumps, compressors, or HVAC systems

• Upstream protection of branch circuits

• Power distribution systems requiring monitoring or automation

• Industrial and commercial electrical systems with high fault currents

Installation and Usage Recommendations

To maximize safety and reliability, follow these best practices:

Ensure Selective Protection

Match MCCB trip curves with downstream MCBs to ensure only the nearest fault point disconnects.

Tighten Terminals with Proper Torque

Loose connections cause overheating. Always follow the manufacturer’s torque specifications.

Provide Sufficient Space for Heat Dissipation

Avoid overcrowding inside the distribution box; heat buildup reduces lifespan.

Regular Maintenance

Inspect at least every 1–2 years:

• Check contact wear

• Clean dust buildup

• Re-tighten terminals

• Test trip mechanism

How to Select the Right MCCB (Quick Guide)

When choosing an MCCB as the main switch, consider:

• Rated current (In)

• Breaking capacity (Icu)

• Load type

• Installation method (front/rear)

• Need for adjustable settings

• Accessory requirements (under-voltage release, shunt trip, etc.)

For incoming mains, breaking capacity must always exceed the maximum expected short-circuit current.

Frequently Asked Questions (FAQ)

Can an MCCB be used as the main switch in a distribution box?

Yes. Its breaking capacity, protection functions, and durability make it ideal for the incoming main circuit.

What is the difference between MCCB and MCB?

• MCCB: high breaking capacity, adjustable settings

• MCB: small loads, fixed settings, lower protection capability

Is an MCCB better than an isolator for the main switch?

Yes. Isolators only provide disconnection; MCCBs provide both isolation and full protective functions.

How do I choose the correct MCCB size?

Select based on rated current, breaking capacity, and actual load requirements.

Can MCCBs support remote monitoring?

Yes. Adding accessories enables remote control, protection signaling, and integration with automated systems.

Conclusion

Using an MCCB as the main switch in a distribution box offers unmatched advantages in safety, reliability, and configurability. With high breaking capacity, integrated protection, adjustable settings, long service life, and expandable features, MCCBs provide a robust and intelligent safeguard for modern power systems.

A correctly selected and properly installed MCCB ensures long-term stability and forms the foundation of a safe and efficient distribution network.