Transformer-protection circuit breaker, SIRIUS size S0
The breaker is rated for a 5.5 kW transformer at 230 V and carries a 25 kA interrupting capacity at 400 V (55 kA AC at 400 V), with a maximum 100 kA at 240 V. It mounts on a 35 mm DIN rail per DIN EN 60715, using either screw or snap-on fastening, and accepts spring-loaded terminals for the main circuit — 2× (1 to 10 mm²) solid or stranded.
The breaker occupies the S0 frame size: 45 mm wide, 119 mm tall, 97 mm deep. Clearance requirements: 50 mm upward, 50 mm downward, 30 mm to the side, zero forward or backward. These are the minimum free-air gaps for arc quenching and thermal dissipation — a panel builder must respect them, not just the DIN-rail footprint.
Interrupting capacity and back-up fuse coordination
The interrupting capacity varies by voltage: 100 kA at 240 V (AC), 55 kA at 400 V (AC), 10 kA at 500 V (AC), 4 kA at 690 V (AC). For installations where the prospective fault current exceeds these values, the breaker must be backed by upstream gG fuses: 63 A at 400 V, 50 A at 500 V, 50 A at 690 V. The maximum switching frequency is 15 operations per hour for AC-3 and AC-3e duty — this is a protection device, not a switching contactor; repeated cycling above that rate will degrade the thermal bimetal calibration.