The Siemens 3RV1421-1CA10-0BA0 is a SIRIUS circuit breaker specifically designed for transformer protection.
The 45 mm width means it takes a single modular slot — factor that into your enclosure fill count. Screw-type terminals on both main and auxiliary circuits accept solid or stranded wire: 2x (1 to 2.5 mm²) or 2x (2.5 to 6 mm²), plus 2x (14 to 10 AWG). Strip length and torque aren't listed here, but the terminal design is standard for the SIRIUS family. Mounting position is any, so no derating for side or inverted orientation.
Breaking capacity and fault clearing
The interrupting rating is voltage-dependent: 100 kA at 240 V, 400 V, and 500 V AC, dropping to 8 kA at 690 V AC. The 8 kA at 690 V still covers the majority of 690 V distribution systems, but if your fault current exceeds that, you'll need to coordinate with a higher-rated upstream device.
Environmental and protection specs
Operates from -50 to +60 °C, stores and ships from -50 to +80 °C — fine for unheated warehouses or outdoor cabinets in temperate climates.
Power dissipation and switching frequency
At rated load in hot operating state, the breaker dissipates 7.25 W total, or 2.4 W per pole. That's low enough to ignore in most enclosures, but if you're packing dozens of these in a sealed box, sum the dissipation and check the temperature rise. Maximum switching frequency is 15 operations per hour at AC-3 duty — fine for infrequent transformer switching, not for a cycling load like a welding gun.