RCBOs

RCBOs, or Residual Current Circuit Breakers with Overcurrent protection, are protective devices used in electrical installations to provide both earth-fault protection and overcurrent protection in a single unit. They integrate a residual-current device (RCD) that senses imbalance between live and neutral currents and an overcurrent device (MCB) that trips on overload or short-circuit conditions. If a fault causes leakage to earth, or if current exceeds the device’s rated limit, the RCBO rapidly disconnects the affected circuit.

Operation and features: An RCBO continuously monitors the current flowing in the circuit conductors. A residual current above its sensitivity value (commonly around 30 mA for human protection, with other values available) triggers the RCD function, opening the circuit. Separate overcurrent protection trips when the current exceeds the device’s rated carrying capacity or during a short circuit. Many RCBOs are available in single-pole + neutral (1P+N) or double-pole + neutral (2P+N) configurations, and in various trip curves and current ratings to suit different circuits. They also include a test button to verify both leakage and overcurrent protection.

Applications and advantages: RCBOs are commonly used in residential and small commercial consumer units to provide selective, space-saving protection for individual circuits. By combining RCD and MCB functions, they simplify installation and reduce the number of devices required, while offering rapid disconnection for both leakage and overcurrent faults. They also help minimize nuisance tripping on adjacent circuits since each circuit can be individually protected.

Installation and maintenance: RCBOs should be installed by qualified personnel in accordance with local electrical codes. Regular testing is advised; the built-in test button should be used to verify operation. If an RCBO trips, the underlying fault must be identified and remedied before resetting.