Each circuit in the distribution box is equipped with a residual current device RCD

Fixed RCDs and RCBOs are the most commonly used residual current devices in distribution boxes, providing protection against electric shock and earth leakage.Fixed RCDsFixed RCDs, also known as RCCBs (Residual Current Circuit Breakers), are installed in the distribution board to provide continuous protection for an entire circuit. They monitor the current flowing through the live and neutral conductors and trip the circuit if an imbalance is detected, indicating leakage to earth. Typical residential RCDs have a tripping current of 30 mA, which is sufficient to protect humans from electric shock, while industrial RCDs may have higher ratings, such as 100–500 mA, for fire protection purposes .RCBOsAn RCBO (Residual Current Breaker with Overcurrent protection) combines the functionality of an RCD and a miniature circuit breaker (MCB). This device protects individual circuits against both earth leakage and overcurrent (overload or short circuit). RCBOs are commonly used in modern homes to protect specific circuits, such as kitchen or bathroom circuits, where both shock and overcurrent protection are required .RCD Types by Residual Current DetectionRCDs are classified based on the type of residual current they can detect:Type AC: Detects standard sinusoidal AC residual currents; suitable for general use .Type A: Detects AC and pulsating DC residual currents; used for circuits with electronic devices like single-phase class 1 loads .Type F: Detects AC, pulsating DC, and high-frequency residual currents; suitable for circuits with variable speed drives or appliances with frequency converters .Type B: Detects AC, pulsating DC, smooth DC, and multi-frequency residual currents; used for three-phase rectifiers, PV systems, EV chargers, and medical equipment . For most residential distribution boxes, Type AC or Type A RCDs are sufficient, while Type F or B may be required for circuits with electronic or variable-speed equipment.Installation ConsiderationsRCDs are wired like MCBs, with line and neutral incoming wires connected to the input terminals and outgoing wires connected to the load circuit .They do not provide overcurrent protection unless integrated as an RCBO, so MCBs are often used in conjunction with RCDs for full protection.Fixed RCDs provide protection for multiple circuits, whereas RCBOs protect individual circuits, allowing selective tripping and easier fault isolation . In summary, distribution boxes typically use fixed RCDs (RCCBs) for general protection and RCBOs for individual circuit protection, with the choice of Type AC, A, F, or B depending on the type of load and residual current characteristics.