The Siemens 5SM1344-6KK03 is a 4-pole SENTRON 5SM1 residual current circuit breaker (RCCB) rated for 40 A at 400 V AC, with a 30 mA residual trip threshold and Type A fault current detection. It is an instantaneous-trip design — no intentional short-time delay — so it responds to earth faults within the natural operating time of the mechanism. Type A detection covers sinusoidal AC residual currents plus pulsating DC residual currents, which covers most modern electronic loads like switched-mode power supplies and single-phase drives.
The 40 A continuous rating holds at ambient temperatures up to 45 °C without derating. Above that, the current must be reduced: 38.4 A at 50 °C, 36.8 A at 55 °C, 35.2 A at 60 °C, 33.6 A at 65 °C, and 32 A at 70 °C. Conductor termination accepts solid or stranded copper from 1.5 mm² up to 25 mm², with a tightening torque of 2.5 to 3 N·m on the screw terminals.
Where it goes in the panel
Snap-on DIN rail (REG) mounting, 4 width units, installation depth 55 mm. Mounting position is unrestricted — horizontal, vertical, or flat. Supply can enter from top or bottom. Finger and back-of-hand safe per the IP20X definition. The silicone-free construction (marked yes) is relevant for applications where outgassing must be avoided, such as in clean rooms or sealed enclosures near sensitive contacts.