The Siemens 5SM3621-4 is a 2-pole SENTRON residual current operated circuit breaker (RCCB) rated for 16 A at 230 V AC, with a 300 mA Type B trip characteristic and short-time delayed switching. Type B detection covers smooth DC fault currents up to the rated residual, plus AC and pulsed DC — so it handles variable-speed drives, UPS systems, and PV inverters where pure AC-sensing RCCBs would miss a DC fault. The 10 kA short-circuit current rating (SCCR) means it can safely interrupt a fault at that level without upstream devices needing to clear it first.
What the ratings mean for fit
The 300 mA trip threshold is sized for equipment protection and fire prevention, not personnel shock — 30 mA units cover that. The short-time delay (S) characteristic prevents nuisance tripping when downstream equipment generates brief inrush or leakage spikes, like motor starting or capacitor banks. At 16 A continuous, it's sized for lighting subcircuits, small motor groups, or general socket outlets on a 230 V single-phase supply. The 2-pole (1-phase + neutral) form factor occupies 4 width units (72 mm) on DIN rail, so it needs that space in the distribution board.
Integration notes
Mounts on DIN rail (REG) in any position. The 70 mm installation depth fits standard 80 mm deep enclosures. Terminals accept solid or stranded conductors from 1.5 to 25 mm²; tighten to 2.5–3 N·m. Ambient range is -25 to +45 °C operating, -40 to +75 °C storage. IP20 with connected conductors in an installed distribution board — so it's panel-internal, not washdown-rated. The top or bottom supply position works for most layouts, and the SIGRES function remains active in the off state when fed from the bottom.