MCCB

Molded Case Circuit Breaker (MCCB) is a type of electrical protection device that provides overcurrent protection for circuits in low- and medium-voltage distribution systems. MCCBs combine protection for overloads and short circuits and can be reset after tripping. They are larger and offer higher current ratings than miniature circuit breakers (MCBs).

Construction and operation: The device is housed in a rigid insulating molded case. It contains a thermal element (bimetal) for overload protection and a magnetic element for short-circuit protection. The trip unit can be fixed or adjustable, allowing setting of the rated current and, in many models, the long-time and instantaneous trip characteristics. The case includes terminals for line and load connections and is designed to interrupt fault currents with a specified breaking capacity (Icu).

Ratings and performance: MCCBs cover current ratings roughly from several tens of amperes up to several thousand amperes in common industrial frames; many designs go higher in specialized equipment. They provide breaking capacities ranging from several to tens of kiloamperes at the rated voltage. Trip curves (for example, B, C, D) describe the time-current relationship for overloads and short circuits. Some MCCBs use electronic trip units offering advanced protection features such as selective protection, adjustable instantaneous trips, or communications capabilities.

Applications and comparison: Used in distribution boards, motor control centers, and feeders within commercial, industrial, and some utility installations. They offer adjustable current settings and modularity for feeders and busbar arrangements and are suitable where higher fault currents or greater protection coordination are required than standard MCBs. MCCBs differ from MCBs in having higher current ratings, adjustable trip settings, and broader protective functions.

Standards: Global MCCBs are designed to comply with international standards such as IEC 60947-2, and in North America with UL 489 for molded case circuit breakers. Product families may also meet regional standards such as CSA. Proper selection depends on voltage, fault current, coordination, and environmental conditions.