What this RCCB does on the line
The Siemens 5SM3344-0LB01 is a 2-pole residual current operated circuit breaker (RCCB) from the SENTRON 5SM3 series, rated 40 A at 230 V AC with a 30 mA trip threshold.
Fit and integration for the panel
Mounts on DIN rail (REG) in any position — no orientation restrictions. Occupies 4 width units (roughly 72 mm on a standard DIN rail). Terminals accept solid or stranded conductors from 1.5 to 25 mm²; tighten to 2.5–3 N·m with a screwdriver.
Why short-time delayed matters
This is a short-time delayed RCCB (Type AC, short-time delayed per,). The delay means it tolerates brief inrush currents — like those from capacitor banks, motor starting, or downstream surge protectors — without nuisance tripping. The 3 kA surge current resistance backs that up. For a line-side RCCB feeding multiple circuits, the short-time delay gives selectivity: a hard fault on a downstream branch trips the branch breaker first, while the RCCB holds. If you need instantaneous trip for a dedicated circuit, you'd look at a non-delayed unit; for a main or feeder RCCB this delay is the right call.