The Siemens 3RV1421-4BA10 is a SIRIUS-brand circuit breaker specifically designed for transformer protection. The trip class is CLASS 10, which means it will clear a fault within 10 seconds at a given multiple of the rated current — a standard for motor and transformer branch circuits.
The main circuit terminals accept solid or stranded wire: two conductors from 1 to 2.5 mm², or two from 2.5 to 6 mm². For AWG, that's 2x (14 to 10) on the main contacts. Auxiliary and control circuits use screw-type terminals with the same wire ranges. The housing is 45 mm wide, 97 mm tall, and 96 mm deep, with zero clearance needed at the back or sides. Front-side IP20 finger-safe protection means you can work near it without worrying about accidental contact.
Breaking capacity and environment
Breaking capacity varies with voltage: 100 kA at 240 V, 50 kA at 400 V, 10 kA at 500 V, and 4 kA at 690 V AC. Surge voltage resistance is rated at 6,000 V, and shock resistance is 25g for 11 ms — tough enough for most industrial panels. Power dissipation in hot operating state is 10.5 W total, or 3.5 W per pole. The maximum switching frequency at AC-3 duty is 15 operations per hour.