Molded Case Circuit Breaker Vs Insulated Case Circuit Breaker

Introduction

Circuit breakers are essential for safe and reliable low-voltage distribution.
But when it comes to MCCBs (Molded Case Circuit Breakers) and ICCBs (Insulated Case Circuit Breakers), confusion is common.

Both devices provide protection, but their performance, construction, and applications are different.
As an engineer who has specified and installed both, I’ll break down their differences and share when to use one over the other.

What is a Molded Case Circuit Breaker (MCCB)?

A Molded Case Circuit Breaker (MCCB) is the standard protective device in low-voltage systems.

• Standards: IEC 60947-2, UL 489.

• Current range: 10A – 2500A.

• Voltage rating: up to AC 690V, some models support DC 1000V.

• Breaking capacity (Icu/Ics): 25kA – 100kA.

• Trip units:

  • Thermal-magnetic (simple, cost-effective).

  • Electronic (adjustable, supports long-time, short-time, instantaneous, and sometimes ground fault).

Field experience: I often use MCCBs as branch feeders or motor protection breakers in factories. They are compact, affordable, and reliable for most downstream loads.

What is an Insulated Case Circuit Breaker (ICCB)?

An Insulated Case Circuit Breaker (ICCB) is essentially a high-performance MCCB. It is designed for heavy-duty and mission-critical applications.

• Standards: closer to ANSI C37 and NEMA AB-3.

• Current range: 800A – 5000A.

• Breaking capacity: up to 150kA.

• Short-time withstand current (Icw): yes, unlike MCCBs.

• Structure:

  • Stored-energy mechanism.

  • Draw-out construction for maintenance.

• Trip units: always electronic, with full protection (L/S/I/G).

Field experience: In a data center job, I specified ICCBs for the main incomers. They provided zone selective interlocking (ZSI) with downstream MCCBs. This avoided unnecessary upstream trips during feeder faults, improving uptime.

Standards and Certification Differences

This is where many articles fall short.

• MCCBs are tested under IEC 60947-2 or UL 489.

• ICCBs overlap with low-voltage power circuit breakers (LVPCBs). Some models comply with ANSI C37 or NEMA AB-3.

Key difference:

• MCCBs provide ultimate breaking capacity (Icu) only.

• ICCBs support short-time withstand (Icw). That means they can coordinate with other breakers and hold through short delays without failing.

As a designer, this distinction is critical in systems with high short-circuit levels.

Rated Current, Voltage, and Breaking Capacity

Here are the expanded comparison points:

Parameter	MCCB	ICCB
Rated current (In)	10–2500A	800–5000A
Rated operational voltage (Ue)	AC 690V / DC 1000V	AC 1000V / DC 1200V
Rated insulation voltage (Ui)	~1000V	1200V or higher
Ultimate breaking capacity (Icu)	25–100kA	65–150kA
Service breaking capacity (Ics)	50–75% of Icu	~100% of Icu
Short-time withstand current (Icw)	Not available	Available
Poles	2P / 3P / 4P	3P / 4P (mostly draw-out)
Mechanical life	5,000–10,000 ops	>10,000 ops
Electrical life	1,500–5,000 ops	>5,000 ops

Key insight: MCCBs are versatile, but ICCBs dominate when fault levels are high, or when coordination and short-time withstand are mandatory.

Trip Units and Protection Functions

MCCB:

• Thermal-magnetic trip is common.

• Electronic trip adds adjustability, but only limited settings.

ICCB:

• Always electronic.

• Offers long-time, short-time, instantaneous, and ground-fault functions.

• Supports ZSI (Zone Selective Interlocking) for better selectivity.

Real case: In a hospital project, the ICCB on the bus-tie provided short-time delay. A downstream MCCB fault did not trip the tie breaker. This saved critical medical loads from blackout.

Structural and Mechanical Design

This is a fundamental difference.

MCCB construction:

• Molded plastic case, compact design.

• Fixed installation, usually not serviceable.

• Operated directly by a handle mechanism.

• Best for circuits where replacement is acceptable after end of life.

ICCB construction:

• Heavy-duty insulated case with stored-energy mechanism (spring-charged). Ensures consistent opening and closing force.

• Draw-out design: breaker can slide in and out of its housing, enabling safe maintenance and replacement.

• Components like contacts and trip units are serviceable, extending lifespan.

• Stronger arc chambers, designed for higher fault energy.

Engineer’s perspective:
If downtime is expensive, ICCBs are superior. In projects like hospitals and data centers, we chose ICCBs because they can be maintained without full system shutdown.

Application Scenarios and Selection Guide

Choosing between MCCB and ICCB depends on current level, fault capacity, and system criticality.

Use MCCB when:

• Current is below 800A.

• Application is a branch or feeder.

• Budget is tight.

• Short-circuit capacity is moderate (<50kA).

Use ICCB when:

• Current is above 800A and up to 5000A.

• Device is main incomer or bus-tie.

• Fault levels are high (65kA+).

• System demands selective coordination with ZSI.

• Maintenance access is critical (draw-out).

• Safety committees require arc-flash mitigation features like ERMS.

Real-world example:

• A factory workshop feeder (250A) → MCCB.

• A 1600kVA transformer incomer (65kA fault level) → ICCB.

• A hospital bus-tie → ICCB with short-time delay for selectivity.

Maintenance, Safety, and Lifecycle Cost

• MCCB: replace when failed. Low upfront cost, higher downtime cost.

• ICCB: higher upfront cost, but lower lifecycle cost due to serviceability.

• Safety: ICCBs integrate communication, monitoring, and arc-flash reduction (ERMS).

In long-term projects, ICCBs often pay back their higher price by minimizing downtime.

Smart Functions and Future Trends

• MCCB: limited auxiliaries (shunt trip, undervoltage release).

• ICCB: full smart package (Modbus/Profibus, energy metering, event logging).

• Future: ICCBs will dominate in smart grids and digitalized factories.

MCCB vs ICCB – Which One Should You Choose?

There’s no one-size-fits-all. The right breaker depends on:

• System size: MCCB for feeders, ICCB for incomers.

• Fault levels: MCCB for moderate, ICCB for high.

• Selectivity needs: ICCB with ZSI ensures proper coordination.

• Maintenance philosophy: MCCB is replace-and-forget. ICCB is maintain-and-reuse.

• Budget vs downtime cost: MCCB is cheaper upfront. ICCB saves costs in critical systems over time.

Simple rule of thumb:

• Small current and simple distribution → MCCB.

• Large current, high fault level, critical power → ICCB.

Final Comparison Table

Aspect	MCCB	ICCB
Standards	IEC 60947-2 / UL 489	ANSI C37 / NEMA AB-3 (closer to LVPCBs)
Current range	10–2500A	800–5000A
Voltage range	Up to 690V AC / 1000V DC	Up to 1000V AC / 1200V DC
Breaking capacity (Icu/Ics)	25–100kA / 50–75% Icu	65–150kA / ~100% Icu
Short-time withstand (Icw)	Not available	Available
Trip units	Thermal-magnetic or basic electronic	Advanced electronic, L/S/I/G
Coordination	Limited	Full selectivity with ZSI
Structure	Molded case, fixed, compact	Insulated case, draw-out, stored-energy mechanism
Serviceability	Replace when failed	Serviceable (contacts, trip unit)
Mechanical life	5,000–10,000 ops	>10,000 ops
Safety	Basic	Arc-flash mitigation (ERMS), better insulation
Smart features	Minimal (auxiliary contacts, shunt trip)	Full digital (communication, metering, logging)
Applications	Branch circuits, feeders, motors	Main incomers, bus-ties, critical loads
Lifecycle cost	Low upfront, higher downtime cost	Higher upfront, lower lifecycle cost

Conclusion

MCCBs and ICCBs are not competitors. They are complementary tools.

• MCCB: the reliable workhorse for feeders and general distribution.

• ICCB: the high-performance choice for mains, critical systems, and facilities where uptime and safety matter most.

From experience, the right choice depends on load size, fault level, selectivity, and maintenance needs.
Making the right decision here protects not just your equipment, but also people, processes, and long-term operational continuity.