What this MCB is and what the ratings mean
The Siemens 5SY4508-8CV is a 1P+N miniature circuit breaker from the SENTRON 5SY series, rated for an ultimate short-circuit breaking capacity (Icu) of 15 kA at 230/400 V AC. The D8 tripping characteristic means it holds through inrush currents 10–20× rated current before opening — sized for motor or transformer branch circuits where the starting surge would nuisance-trip a B- or C-curve breaker. The 1P+N configuration switches the line pole and provides a switched neutral that opens with the line, not a solid neutral bar. 15 kA Icu at 400 V puts this breaker into the high-fault category for a residential or light-commercial panel board. At 230 V the Icu is the same 15 kA, which covers most utility transformer secondary faults in European-style TN systems. The D8 curve is the key selection gate: if the downstream load is resistive or general-purpose, a C-curve sibling would coordinate better; this one is for the branch that sees a motor start or capacitor bank inrush.