Siemens 5SY8550-7 — SENTRON MCB, C-Curve, 1P+N, 25 kA
The Siemens 5SY8550-7 is a SENTRON miniature circuit breaker (MCB) in a 1P+N configuration — one protected pole plus a switched neutral — with a C-curve trip characteristic. It is rated for 25 kA breaking capacity at 230 V AC per IEC 60947-2, and 15 kA at 60 V DC per the same standard. For UL 1077 recognition, the interrupting rating is 5 kA. The 36 mm width (2 modular units) and 76 mm depth fit standard DIN-rail enclosures; the neutral conductor is switched, so this unit serves single-phase circuits where both line and neutral need isolation on fault.
Breaking capacity and selectivity — what the ratings mean
The 25 kA IEC rating at 230 V AC is the maximum prospective fault current this MCB can safely interrupt under standard test conditions. For a panel designer, that figure governs the upstream fuse or breaker coordination — you need a device with equal or higher breaking capacity ahead of it to maintain selectivity. The 15 kA DC rating at 60 V applies to battery-backed or DC bus circuits, common in industrial control panels. The UL 1077 5 kA rating is the supplementary-protector limit for North American installations; if the available fault current at the panel exceeds 5 kA, the 5SY8550-7 must be backed by a branch-circuit rated OCPD.
Mounting, environment, and accessories
Snap-on mounting to DIN rail, any position. The 70 mm installation depth leaves clearance for rear-connected busbars. Operating temperature range spans -40 °C to 75 °C, with humidity derating above 55 °C (max 95% RH at 55 °C, dropping to 35% at 75 °C). Pollution degree 3 and overvoltage category III suit industrial environments. The housing is halogen-free and silicon-free. Supplementary devices (auxiliary switches, shunt trips, undervoltage releases) can be installed on the right side. Vibration resistance per IEC 60068-2-6: ±1 mm at 5–25 Hz, 50 m/s² at 25–150 Hz. Mechanical endurance is 10 000 operating cycles typical.