The Siemens 5SM3344-6LB01 is a SENTRON residual current operated circuit breaker (RCCB) — 4-pole, type A, short-time delayed, rated 40 A at 400 V AC with a 30 mA trip threshold. Type A means it detects pulsating DC residual currents on top of sinusoidal AC, so it covers rectifier-fed loads like VFDs, switching power supplies, and modern lighting ballasts that a plain AC-type RCCB would miss. The 30 mA trip provides personal protection against direct contact; the 40 A continuous rating matches a typical submain or feeder feeding a mixed load panel. Short-time delayed (selective) design means it withstands brief inrush without tripping, coordinating with downstream MCBs so only the faulted branch opens — not the whole panel. Rated short-circuit withstand is 10 kA, surge current resistance 3 kA, so it holds under fault conditions that would weld contacts on a standard RCCB.
Panel integration
Snaps onto DIN rail (REG mounting), occupies 4 width units (about 72 mm at 18 mm/module). Mounting position any; supply feed top or bottom, no orientation restriction. Terminal torque spec is 2.5 to 3 N·m, accepting solid or stranded copper from 1.5 up to 25 mm² — enough for the 40 A feed without pigtailing down. Finger and back-of-hand safe terminals reduce arc-flash exposure during live troubleshooting.