What Is a Molded Case Circuit Breaker (MCCB)?

Published: 2025-06-10 | 8 min read | Category: Technical Guide

A molded case circuit breaker (MCCB) is a type of circuit breaker enclosed in a molded insulating housing that provides protection against overcurrent, short circuits, and ground faults in commercial and industrial electrical systems rated from 15A to 2,500A. MCCBs are the most widely used circuit breaker type in commercial buildings, accounting for over 70% of all breakers installed in US commercial electrical distribution systems.

MCCBs differ from residential miniature circuit breakers (MCBs) in three key ways: higher interrupting capacity (14,000-200,000 AIC vs. 10,000 AIC), adjustable trip settings on many models, and the ability to handle higher continuous currents. They differ from air circuit breakers (ACBs) in that they use a sealed, non-maintainable housing rather than an open, field-serviceable design.

MCCB Specifications at a Glance

| Specification | Typical Range | |---|---| | Current rating | 15A - 2,500A | | Voltage rating | 240V - 600V AC | | Interrupting capacity | 14,000 - 200,000 AIC | | Number of poles | 2-pole or 3-pole | | Trip type | Thermal-magnetic or electronic (LSIG) | | Frame sizes | A, B, C, D, E, F, H, J, K, L, M, N, P |

**Key takeaway:** MCCBs are the workhorse of commercial electrical distribution. If you're working on any building larger than a single-family home, you're working with MCCBs.

How MCCBs Work

An MCCB uses two protection mechanisms: a thermal element (bimetallic strip that bends under sustained overcurrent, providing time-delayed trip for overloads) and a magnetic element (electromagnetic coil that trips instantly for short circuits). Electronic trip units replace these mechanical elements with current transformers and microprocessors, offering adjustable LSIG (Long-time, Short-time, Instantaneous, Ground fault) protection curves.

The "molded case" refers to the glass-polyester or thermoset housing that encapsulates the entire mechanism. This housing provides electrical insulation, arc containment, and environmental protection — but it also means the breaker is not field-serviceable. When an MCCB fails, it's replaced as a complete unit.

Common MCCB Brands and Series

| Manufacturer | Series | Frame Sizes | Typical Application | |---|---|---|---| | Square D | PowerPact | H, J, L, M, P | Commercial distribution, switchboards | | Eaton | PowerDefense | G, F, J, K, L | Commercial/industrial panels | | Siemens | Sentron 3VA | VL160-VL1600 | Commercial buildings, OEM | | GE | Record Plus | F, J, K, L | Industrial distribution | | ABB | Tmax XT | XT1-XT7 | Global industrial |

AllBreakerSales.com stocks MCCBs from all major manufacturers in new, surplus, and reconditioned condition — from 15A residential-grade frames to 2,500A industrial units. Call **(877) 611-0034** for same-day quotes on any MCCB catalog number.

Shop These Breakers

Popular models available for immediate shipping:

• Square D JDA36200
• Eaton HFD3100
• Siemens FXD63B200

Call **(877) 611-0034** for pricing on any circuit breaker in our inventory.

Frequently Asked Questions

What is the difference between an MCCB and a regular circuit breaker?

A molded case circuit breaker (MCCB) is a type of circuit breaker — the term refers to the construction where the operating mechanism, contacts, and arc extinguishing system are enclosed in a molded insulating case. MCCBs are used for commercial and industrial applications at higher amperages and voltages than residential breakers.

What amperage range do MCCBs cover?

MCCBs typically cover the range from 15A to 2500A, though the upper range (above 1200A) is increasingly served by insulated case circuit breakers (ICCBs) and air circuit breakers (ACBs). The most common commercial MCCB range is 100A to 800A.

What is an LSIG trip unit in an MCCB?

LSIG stands for Long-time, Short-time, Instantaneous, and Ground fault protection. An LSIG electronic trip unit provides all four protection functions with adjustable settings, allowing the breaker to be precisely coordinated with other protective devices in the system. This is more flexible than a fixed thermal-magnetic trip unit.