What it is and what it does
The Siemens 3RV1021-1HA10-ZW95 is a SIRIUS motor protection circuit breaker — a 3-pole device sized for a 3 kW motor at 400 V AC, with a continuous current rating of 8 A and Trip Class 10 thermal overload protection. The 100 kA breaking capacity at 400 V AC means it can safely interrupt a fault current up to that level without upstream fuses needing to clear first — a real advantage in high-fault panels where selectivity matters. Phase failure detection is built in, so a lost phase on the line side trips the breaker rather than letting the motor single-phase and burn.
Mounting and integration
Snap-on mounting onto 35 mm DIN rail per EN 50022, or screw-fasten if the rail isn't an option. Any mounting position works. The 45 mm width and 96 mm depth fit standard panel layouts without surprises. Screw terminals on both main and auxiliary circuits accept 1 to 2.5 mm² solid or stranded (two conductors per clamp), or 2.5 to 6 mm² for a single conductor. AWG 14 to 10 equivalent. Zero clearance needed at the sides or rear — 0 mm backwards and side spacing. IP20 on the front face means finger-safe from the panel front; the body itself is open-frame behind the panel, so enclosure selection needs to account for that.
What the ratings mean for your panel
Trip Class 10 means the thermal bimetal trips within 10 seconds at 7.2× the current setting — standard for standard-duty motor starting where the acceleration time is under 10 seconds. For longer ramp times (high-inertia loads), a Class 20 or 30 would be needed. The 15 operations per hour maximum at AC-3 duty governs how often you can cycle this breaker under motor load — fine for a pump or fan cycling a few times an hour, but not for a rapid-reversing application. Rated insulation voltage 690 V, surge voltage resistance 6 kV. Power dissipation 9.25 W at rated current (3.1 W per pole).