The Siemens 5SM3344-0KL is a 4-pole SENTRON residual current operated circuit breaker (RCCB), type AC, rated 40 A with a 30 mA trip threshold at 400 V AC — the standard residential and light commercial ground-fault protection package for three-phase networks where neutral is brought in on the left side of the device. The 30 mA sensitivity is the common touch-safe threshold per IEC 60364, meaning it clears leakage currents that would be hazardous to a person making contact with an energized enclosure. It is an instantaneous (non-time-delayed) design — no intentional delay before tripping on a ground fault — so it responds immediately to sinusoidal AC residual currents at the mains frequency of 50 Hz.
The 30 mA trip threshold is the standard for personal protection against electric shock; it will not coordinate with a 30 mA upstream RCCB — if selectivity is needed between two RCCBs, the downstream unit must be a time-delayed (S-type) or a lower-threshold device. Ambient temperature range of -5 to +45 °C covers most indoor panel environments, but at sustained temperatures above 40 °C the continuous current rating should be derated per the manufacturer's thermal curve — the 40 A rating is at a reference ambient, typically 30 or 35 °C.
Snaps onto standard DIN rail (REG profile), occupies 4 width units (roughly 72 mm), and installs in any orientation — top or bottom feed, horizontal or vertical rail, no restriction. Installation depth is 70 mm from the rail — fits flush in a standard 125 mm deep distribution board; check the gland plate clearance if you're running conductors behind the device. Terminals accept solid or stranded conductors from 1.5 to 25 mm² — covers everything from a 2.5 mm² lighting circuit tail up to a 16 mm² feeder; tighten to 2.5 to 3 N·m with a screwdriver, no special torque tool needed. The N-left variant means the neutral pole is on the left side of the device when viewed from the front — if you're replacing an existing RCCB that has neutral on the right, you'll need to swap the incoming and outgoing conductors or use a different variant.