It sits between the contactor and the supply in a motor starter assembly, combining the overload relay and short-circuit protection in one device.
Interrupting capacity — the real-world breaker
Phase failure detection — why it matters
If one supply phase drops out, the breaker trips — preventing single-phasing, which draws high current in the remaining windings and burns a motor fast. This is a standard feature on SIRIUS motor-protective breakers, not an option card.
The 45 mm width (three module spaces) and 75 mm depth leave room for adjacent contactors and terminals. Any mounting position is allowed. The screw-type terminals for the main circuit accept 2×(0.5…1.5 mm²) or 2×(0.75…2.5 mm²) solid or stranded — common for motor feeds up to the rated current. Clearance: 20 mm above and below, 9 mm to the side, zero forward and backward.