It's the RCD half of an RCBO combination — mates with the 5SY series MCB (2-module width) to build a combined unit. Type A means it catches pulsating DC fault currents from rectified loads (SMPS, LED drivers, VFDs) that a plain AC type would miss.
Occupies 2 modular width units (71 mm) on DIN rail, 70 mm deep — standard for a 2-pole RCD in a distribution board. IP20 with conductors connected; mount in any position. Supply feeds top or bottom. Fastens via standard REG clip. The 70 mm depth clears most domestic enclosures but check shallow consumer units — some budget boards only take 65 mm.