Residual current circuit breakers (RCCBs) possess high sensitivity and rapid operation in detecting electric shock and protecting against residual current, unmatched by other protective electrical devices such as fuses and automatic switches. Automatic switches and fuses normally carry load current, and their protection settings must exceed the normal load current; therefore, their primary function is to interrupt phase-to-phase short-circuit faults (some automatic switches also have overload protection). RCCBs, on the other hand, utilize the residual current of the system for reaction and operation. During normal operation, the residual current in the system is almost zero, so its operating setting can be set very small (generally in the mA range). When a person experiences electric shock or the equipment casing becomes energized, a larger residual current appears. The RCCB detects and processes this residual current and reliably operates to cut off the power supply.
When electrical equipment leaks current, it will present an abnormal current or voltage signal. The RCCB detects and processes this abnormal current or voltage signal, causing its actuator to operate. We call a residual current device (RCD) that operates based on fault current a current-type RCD, and an RCD that operates based on fault voltage a voltage-type RCD.
