The Schneider Electric Acti 9 iPRU 4P 20R is a Type 2 (Class II) Surge Protective Device designed for the main distribution board in three-phase electrical systems. The "20R" suffix indicates it is a special version with a built-in thermal disconnector, making it a "plug-and-play" SPD that does not require an external backup fuse or circuit breaker for most applications. It provides protection against transient overvoltages from indirect lightning strikes and switching surges.