The Siemens 5SL7404-8RC is a 4-pole miniature circuit breaker (MCB) rated for 415 V AC with a 15 kA breaking capacity and a D tripping characteristic for a 4 A rated current.
That is a utility-grade interrupting rating — it belongs in a panel where the transformer and upstream feeder can deliver that kind of fault energy, not in a light commercial board where 6 kA or 10 kA would suffice. The 4-pole construction (all poles switched, neutral switched as well) means it is intended for a three-phase four-wire system where you need to isolate all live conductors. The D 4 characteristic: 4 A continuous rating, with the magnetic trip set to operate between 40 A and 80 A. That is deliberately high, so a motor starting transient of 6–8× FLA will not clear the breaker on start-up provided the fault loop impedance keeps the current below the instantaneous threshold.
This is a DIN-rail-mount MCB, 4-pole wide, occupying four modular units (each 17.5 mm or 18 mm depending on the standard). The D 4 characteristic means the thermal bimetal element is sized for 4 A continuous; if the ambient temperature inside the enclosure exceeds 40 °C, derating applies per the IEC 60898-1 thermal correction table — typically about 0.8–0.9× for a 50 °C enclosure. The 15 kA breaking capacity is unconditional at 415 V; no need for a current-limiting upstream device to achieve that rating, which simplifies coordination in a sub-distribution board.