Transformer-protection circuit breaker, 20 A, CLASS 10
The Siemens SIRIUS 3RV1421-4BA10-ZX95 is a motor-protective circuit breaker specifically designed for transformer protection, carrying a 20 A rated continuous current and CLASS 10 trip characteristic. Screw-type terminals on the main circuit accept 2x (1 to 2.5 mm²) solid or stranded, or 2x (2.5 to 6 mm²) — the larger range handles the 20 A feed without pigtails. The auxiliary switch slot is present but unpopulated (0 auxiliary contacts factory-fitted), so plan an add-on block if remote status or fault signaling is needed.
Breaking capacity and trip coordination
Rated breaking capacity drops with system voltage: 100 kA at 240 V AC, 50 kA at 400 V AC, 10 kA at 500 V AC, and 4 kA at 690 V AC. The 6 kV surge voltage resistance (rated impulse withstand) covers standard industrial transient environments. No ground-fault detection on this variant — that requires the 3RV19xx accessory module or an external relay.
Zero mm clearance needed at the sides or rear — stackable against adjacent devices. Shock rated at 25 g for 11 ms, which is typical for panel-mounted breakers in machinery with vibration. Front face carries IP20 finger protection — safe for open-panel installation but not for washdown zones. The 96 mm depth fits standard 100 mm deep enclosures without forcing a taller gland plate.