The Siemens 3RV2421-0HA10 is a SIRIUS circuit breaker specifically designed for transformer protection — not a general-purpose motor-protective breaker. Trip Class 10 means it will trip within 10 seconds at 7.2× the thermal setting — fast enough to protect a transformer winding from through-fault heating, but slower than a motor-protective Class 10A or 5.
Clearance requirements: 50 mm above and below, 30 mm to the side, zero forward or backward. Any mounting position is allowed. The screw-type terminals on the main circuit accept 2×(1–2.5 mm²) solid/stranded or 2×(2.5–10 mm²), M4 screw size, requiring a 5–6 mm diameter screwdriver shaft.
