Circuit breaker

A resettable electrical switch that interrupts current when a circuit experiences specified fault or overload conditions. It protects wiring and equipment by opening the circuit before excessive current causes damage.

Thermal-magnetic circuit breaker: A circuit breaker that combines a heat-sensitive element for overloads with an electromagnetic trip for short circuits. Its paired mechanisms illustrate how one breaker can respond to both sustained overloads and sudden faults.
Electric current: The rate at which electric charge flows through a conductor or circuit. A breaker’s ratings and trip behavior are defined in relation to current.
Fuse: A one-time overcurrent protection device whose element melts to open a circuit. A fuse performs a similar protective role but must be replaced after it operates.
Miniature circuit breaker: A compact low-voltage circuit breaker commonly used to protect individual building circuits. It is the familiar modular breaker used in many residential and commercial distribution boards.
Selective coordination: The arrangement of protective devices so that the device nearest a fault operates before upstream devices. Coordination keeps a local breaker trip from unnecessarily cutting power to a larger part of the system.
Bimetallic strip: A bonded strip of two metals that bends when temperature changes because the metals expand at different rates. Overload current heats this strip until its bending releases the breaker latch.
Overcurrent: Current greater than the amount a circuit or device is designed to carry safely. Breakers are selected to interrupt overcurrent before wiring overheats or equipment is damaged.
Residual-current device: A device that disconnects a circuit when it detects an imbalance between outgoing and returning current. It detects leakage to earth rather than relying on excess load current alone.
Molded-case circuit breaker: A low-voltage circuit breaker enclosed in an insulating molded case, available across a broad range of current ratings. It serves larger branch and feeder circuits than typical miniature breakers.
Electrical protection coordination: The design of protective devices and settings to detect faults and isolate affected parts of an electrical system. Circuit breakers are coordinated with other protective devices to limit outages and equipment damage.

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