What it is and what the ratings mean
The Siemens 5SV3344-3 is a 4-pole residual current operated circuit breaker (RCCB) from the SENTRON series, type F, short-time delayed, rated 40 A with a 30 mA residual operating current on a 400 V AC supply. The 30 mA sensitivity means it detects earth leakage down to that threshold — standard for personal protection against direct contact in IEC 60364 installations. The short-time delayed design (type F) handles pulsed DC and mixed-frequency residual currents common in modern loads with VFDs or power electronics, so it won't nuisance-trip on inverter-fed equipment like pumps or conveyors. Rated short-circuit capacity is 10 kA per IEC 61008-1, which means it can safely interrupt a fault current up to that level without welding contacts or cascading failure upstream. The 4-pole construction switches all three phases plus neutral, making it suitable for three-phase four-wire systems (TN-S, TT) where the neutral must be disconnected with the phases.
Where it goes and how it mounts
Snaps onto a standard 35 mm DIN rail (REG) and occupies 4 modular width units (72 mm wide, 60 mm grid spacing). Mounting position is any orientation, which simplifies panel layout. The 70 mm installation depth matches standard distribution board cutouts. Supply can enter from top or bottom, so you don't need to flip the busbar arrangement when retrofitting into an existing panel. IP20 rating applies when installed in a distribution board with connected conductors — standard for enclosed panels. Overvoltage category III means it's rated for fixed installation downstream of the main distribution board, not for point-of-use equipment. Silicon-free construction avoids outgassing issues in sensitive environments like coating or electronics assembly lines.