When sourcing RCCB relays, you must prioritize Rated Current (In), typically ranging from 16A to 125A, and Rated Residual Operating Current (IΔn), where 30mA is standard for personnel protection and 100mA-500mA for fire protection. Ensure the device features a high short-circuit breaking capacity (Icn) of at least 6kA or 10kA to withstand fault currents. Additionally, verify the Type (AC, A, or B); Type B is increasingly essential for modern installations as it detects smooth DC residual currents common in EV chargers and solar inverters.