What it is and what it does
The Siemens 3RV6021-4AA10 is a SIRIUS motor protection circuit breaker in the S0 frame size — a three-pole thermal-magnetic device rated 16 A operational current at 690 V, 50/60 Hz. The thermal overload release handles the Class 10 trip curve (trips within 10 seconds at 7.2× rated current), and the magnetic short-circuit trip catches hard faults. That 16 A at AC-3 duty (400 V) means it directly protects a motor drawing that full-load current; the 7 W typical power loss tells you it's not a power hog in a crowded panel.
Mounting and integration
Snaps onto 35 mm DIN rail (DIN EN 60715) or screws directly to a backplate — mounting position any. The S0 frame footprint is 45 mm wide by 97 mm tall by 96 mm deep. Clearance: 50 mm above and below, 30 mm to the sides, zero forwards or backwards. That 0 mm forward clearance means it can sit flush against a panel door or busbar cover without extra breathing. Screw-type terminals on top and bottom accept 2×(1…2.5 mm²) solid/stranded or 2×(2.5…10 mm²) — torque to 2…2.5 N·m.
What the ratings mean for your panel
Rated 16 A at AC-3 (400 V) — that's the motor-switching current, not a resistive load. The Class 10 trip curve means it clears overloads fast enough to protect standard IEC motors without nuisance tripping on startup inrush. The 690 V rated value covers 400 V and 480 V systems with headroom. Shock-rated to 25 g / 11 ms per IEC 60068-2-27, so it holds up in mobile or high-vibration installations. Operating temperature -20 to +60 °C, 10-95% RH non-condensing.