Motor protection circuit breaker for 35 mm DIN rail
The Siemens SIRIUS 3RV2021-4NA20-0BA0 is a motor protection circuit breaker in size S0, designed for screw and snap-on mounting onto 35 mm DIN rail per DIN EN 60715. It provides Class 10 trip protection, meaning it will trip within 10 seconds at 7.2× the thermal setting — the standard for standard-duty induction motor starting. Phase failure detection is built in, so a lost phase on the line side will cause the breaker to open, preventing single-phasing damage to the motor. Rated operational voltage spans 20 to 690 V AC, with a maximum AC-3 switching frequency of 15 operations per hour. The spring-loaded terminals accept 2× (1 to 10 mm²) solid or stranded copper. Ambient operating temperature range is -50 to +60 °C; storage and transport tolerance extends to -50 to +80 °C.
Breaking capacity and selectivity
The 3RV2021-4NA20-0BA0 carries a rated ultimate short-circuit breaking capacity (Icu) of 10 kA at 400 V AC, 5 kA at 500 V AC, and 2 kA at 690 V AC. For coordination with an upstream MCCB or fuse, the conditional short-circuit current (Ics) is higher: 25 kA at 400 V AC, 10 kA at 500 V AC, and 4 kA at 690 V AC — these are the values used when the breaker is backed by a gG 63 A fuse (the evidence lists gG 63 A at 400 V, 500 V, and 690 V). This means the breaker can be installed downstream of a 63 A gG fuse and still clear a fault up to 25 kA at 400 V without the fuse needing to open.
Mounting and panel integration
Mounts on standard 35 mm DIN rail per DIN EN 60715 via screw and snap-on fastening. The mounting position is any orientation. Clearance requirements: 50 mm upwards, 50 mm downwards, 30 mm to the side, and 0 mm forwards/backwards — so it can be panel-mounted flush against the backplane. The S0 frame size (45 mm width, 97 mm depth, 119 mm height) is the standard footprint for this class of Siemens motor-protective device.