What Is a Molded Case Circuit Breaker (MCCB)?

Published: 2026-07-02 | 7 min read | Category: Technical Guide

A Molded Case Circuit Breaker (MCCB) is an industrial-grade overcurrent protection device housed in a molded insulating case. MCCBs are the backbone of commercial and industrial power distribution — they protect circuits from 15 amps to 2,500 amps at voltages up to 600V, with interrupting capacities reaching 200,000 amps. If you work in any building larger than a house, you're surrounded by MCCBs.

MCCB vs. Other Breaker Types

| Feature | MCB (Miniature) | MCCB (Molded Case) | ACB (Air Circuit) | |---------|----------------|-------------------|-------------------| | Current range | 1-100A | 15-2,500A | 800-6,300A | | Voltage | 120-240V | 240-600V | 240-600V | | Interrupting capacity | 10-18 KAIC | 14-200 KAIC | 42-200 KAIC | | Trip settings | Fixed | Adjustable (many) | Fully adjustable | | Physical size | Small (1-2" wide) | Medium (3-9" wide) | Large (12"+ wide) | | Mounting | Plug-in/DIN rail | Bolt-on/Plug-in | Drawout | | Typical location | Residential panels | Commercial/industrial panels | Main switchgear | | Maintenance | Replace entire unit | Replace or adjust trip unit | Maintainable in place |

How MCCBs Work

An MCCB contains three protection mechanisms:

1. Thermal Element (Overload Protection) A bimetallic strip heats up as current flows through it. When current exceeds the rating for a sustained period, the strip bends and triggers the trip mechanism. This protects against overloads (110-600% of rated current over seconds to minutes).

2. Magnetic Element (Short-Circuit Protection) An electromagnetic coil generates a magnetic field proportional to current. During a short circuit (thousands of amps), the field becomes strong enough to instantly trigger the trip mechanism. Response time: 1-3 milliseconds.

3. Arc Extinguishing System When the contacts open under fault conditions, an arc forms between them. The MCCB uses arc chutes (a series of metal plates) to split, cool, and extinguish the arc. This is what makes high KAIC ratings possible.

MCCB Frame Sizes

MCCBs are manufactured in standard frame sizes:

| Frame Size | Max Continuous Current | Typical Applications | |-----------|----------------------|---------------------| | 100A Frame | 15-100A | Branch circuits, small feeders | | 150A Frame | 70-150A | Sub-panel feeders | | 250A Frame | 70-250A | Large feeders, small mains | | 400A Frame | 200-400A | Panel mains, motor feeders | | 600A Frame | 250-600A | Switchboard mains | | 800A Frame | 400-800A | Large distribution | | 1200A Frame | 600-1200A | Main service entrance | | 1600A Frame | 800-1600A | Large facility mains | | 2000A Frame | 1000-2000A | Industrial mains | | 2500A Frame | 1200-2500A | Heavy industrial |

Trip Unit Types

Thermal-Magnetic (Standard) - Fixed or adjustable thermal overload - Fixed magnetic instantaneous trip - Most common and least expensive - Suitable for most applications

Electronic Trip (LSI/LSIG) - **L** = Long-time (overload) — adjustable pickup and delay - **S** = Short-time — adjustable pickup and delay (allows coordination) - **I** = Instantaneous — adjustable pickup level - **G** = Ground fault — adjustable pickup and delay

Electronic trip units allow precise coordination between upstream and downstream breakers, ensuring only the breaker closest to the fault trips.

Motor Circuit Protector (MCP) - Magnetic-only trip (no thermal element) - Used for motor branch circuits where a separate overload relay provides thermal protection - Allows high inrush current during motor starting

Selecting an MCCB

When specifying an MCCB, determine:

1. **Continuous current** — size for 125% of continuous load (NEC 210.20) 2. **Voltage** — must equal or exceed system voltage 3. **Interrupting capacity** — must equal or exceed available fault current 4. **Number of poles** — 1, 2, or 3 pole 5. **Trip type** — thermal-magnetic for simple applications, electronic for coordination 6. **Mounting** — fixed (bolt-on) or drawout 7. **Accessories** — shunt trip, undervoltage release, auxiliary contacts, alarm switch

Major MCCB Manufacturers

| Manufacturer | Popular MCCB Lines | |-------------|-------------------| | Square D / Schneider | PowerPact (H, J, K, L, M, P frames) | | Eaton / Cutler-Hammer | Series C (FD, HFD, JD, LD, ND, RD) | | Siemens | Sentron (ED, FD, JD, LD, MD, ND, PD) | | GE | Record Plus (TED, TFK, TFJ, TKM) | | ABB | Tmax (T1-T7) |

Bottom Line

MCCBs are the standard overcurrent protection device for commercial and industrial applications above 100A or above 240V. They offer adjustable protection, high interrupting capacity, and long service life. The AllBreakerSales.com catalog includes MCCBs from every major manufacturer in every frame size. Request a written quote to confirm the required catalog number and current availability. Call (951) 903-9804 for written-quote pricing on any MCCB — new, surplus, or reconditioned.

Shop These Breakers

Popular MCCB models available only when confirmed in the written quote:

• Square D HJA36020 (H-frame, 20A)
• Eaton HFD3100 (F-frame, 100A)
• Siemens FXD63B200 (200A)

Call **(951) 903-9804** to request written pricing for a catalog number.

Frequently Asked Questions

What is the difference between MCB and MCCB?

MCB (Miniature Circuit Breaker) is a small, residential-grade breaker typically rated up to 100A with interrupting capacity up to 10-18 KAIC. MCCB (Molded Case Circuit Breaker) is a larger, industrial-grade breaker rated from 15A to 2,500A with interrupting capacity up to 200 KAIC. MCCBs have adjustable trip settings, higher voltage ratings (up to 600V), and are used in commercial/industrial panels. MCBs are the breakers in your home panel; MCCBs are in commercial buildings and factories.

Where are MCCBs used?

MCCBs are used in commercial buildings, industrial facilities, data centers, hospitals, manufacturing plants, and anywhere that requires higher amperage (above 100A), higher voltage (277-600V), or higher interrupting capacity (above 18 KAIC). They're found in main distribution panels, motor control centers, switchboards, and as feeder breakers protecting downstream panels.

Can an MCCB be used in a residential panel?

No. MCCBs are physically too large for residential load centers and use different mounting systems (bolt-on or drawout). Residential panels accept miniature circuit breakers (MCBs) in plug-in or bolt-on configurations. However, the main breaker in a large residential service (200A+) is technically a small MCCB mounted in a dedicated enclosure.