Selectivity of Residual Current Devices (RCDs)
From Electrical Installation Guide
When circuit breakers are equipped with RCD function, selectivity principles described in previous paragraphs are valid for short-circuit and earth fault with high amplitude current.
Residual Current Devices are by design very sensitive to fault and shall be coordinated properly to achieve total selectivity in case of earth fault, in addition to overcurrent protection selectivity.
For more details on RCDs selectivity, see chapter F - Coordination of residual current protective devices
