Size S0 motor protection breaker — 25 kA at 400 V, Class 10
The Siemens 3RV2021-4AA10-0RT0 is a Size S0 motor protection circuit breaker from the SIRUS 3RV2 family, designed for screw and snap-on mounting onto 35 mm DIN rail per DIN EN 60715. Rated breaking capacity hits 25 kA at 400 V AC (55 kA at 400 V AC for the main circuit) and 100 kA at 240 V AC, giving solid SCCR headroom for most industrial motor branch circuits without cascading upstream. The Class 10 trip characteristic matches standard IEC motor starting profiles — it holds through the inrush and clears on a locked-rotor fault without nuisance tripping. Motor power rating is 4 kW at 230 V, with a maximum AC-3 operating voltage of 690 V. The gG fuse backup ratings are 63 A at 400 V, 50 A at 500 V, and 40 A at 690 V — coordination data for selective coordination studies. Mechanical endurance is listed at 100 000 typical cycles for the main contacts.
The 25 kA at 400 V rated breaking capacity and 55 kA at 400 V for the main current circuit mean this breaker can safely interrupt high fault currents in a 400 V distribution panel — typical for European 400 V three-phase motor branch circuits. These figures are the SCCR the breaker contributes to the panel assembly; coordination with upstream fuses or breakers uses the gG backup ratings provided. Trip Class 10 means the breaker's thermal overload element allows a motor to draw locked-rotor current for up to 10 seconds before tripping — enough for most standard induction motor starts, but not for high-inertia loads that need Class 20 or Class 30. The 15 1/h maximum switching rate at AC-3 duty matches typical process cycling, not high-speed jogging. No ground fault or phase failure detection built in — this is a basic motor protection breaker for overload and short-circuit only. If phase loss or ground fault protection is required, add an external relay or specify a variant with those functions.
For panel builders or MRO planners, the screw-type main circuit terminals accept 2x (1 to 2.5 mm²) or 2x (2.5 to 10 mm²) solid or stranded copper — covers most motor feeder sizes up to 4 kW at 230 V. The M4 main contact screws and Pozidriv size 2 screwdriver tip are standard panel tools.
Integration notes
The 45 mm width occupies one standard 45 mm module slot. Clearance requirements: 50 mm upwards, 50 mm downwards, 30 mm at the sides, zero forwards and backwards. The breaker is designed for any mounting position, so it can be installed horizontally or vertically in tight enclosures without derating the thermal trip.