The Siemens SENTRON 5SY7405-8 is a 4-pole miniature circuit breaker (MCB) with a D tripping characteristic, rated at 0.5 A at AC 50/60 Hz.
The D-curve characteristic (10–20× In magnetic trip) lets the 0.5 A rating pass the magnetizing inrush of a small control transformer or the locked-rotor spike of a fractional-horsepower motor without nuisance tripping. But the thermal element is sensitive to enclosure temperature: at 40 °C ambient the continuous rating derates to 0.48 A, at 50 °C to 0.45 A, and at 60 °C to 0.42 A.
At 4 modular width units (72 mm wide, 90 mm tall, 76 mm deep, 70 mm installation depth), it snaps onto a DIN rail via the quick-assembly system and accepts wiring from top and bottom combined terminals.