An RCBO is a combination device that functions as a Residual Current Device (RCD) and a Miniature Circuit Breaker (MCB) with overcurrent protection. Here is detailed information on how RCBOs work according to BS 7671:
Functionality:
RCBOs provide combined protection against both earth faults (residual current) and overcurrents. They automatically disconnect the circuit in the event of a fault preventing electric shock and fire hazards.
Residual Current Protection:
Similar to standalone RCDs RCBOs monitor the current flowing in the live and neutral conductors. If there is an imbalance indicating a leakage to the ground the RCBO quickly disconnects the circuit to prevent electric shock.
Overcurrent Protection:
RCBOs incorporate the features of an MCB to protect against overcurrents. If the current exceeds the rated capacity of the circuit the overcurrent protection mechanism within the RCBO trips disconnecting the circuit to prevent damage to wiring and appliances.
Types:
RCBOs are available in various types based on their tripping characteristics for both residual current and overcurrent. Common types include Type B Type C and Type D RCBOs each suitable for different applications and environments.
Installation:
BS 7671 provides guidelines on the installation of RCBOs specifying their use in protecting specific circuits. RCBOs are commonly installed in consumer units (fuse boxes) and distribution boards.
Testing:
RCBOs like other protective devices need regular testing to ensure proper functionality. This includes testing both the residual current and overcurrent protection features to verify their correct operation.
Coordination:
Coordination with other protective devices such as upstream circuit breakers is important to ensure the proper operation of the electrical protection system. Discrimination between devices helps localize faults.
Advancements:
BS 7671 is regularly updated to incorporate technological advancements and safety standards. Compliance with the latest edition of the regulations is essential to ensure the use of RCBOs that meet current safety requirements.
RCBOs offer a comprehensive solution for electrical protection by combining residual current and overcurrent protection in a single device. Their correct selection installation and maintenance are crucial for ensuring the safety of electrical installations.