Siemens 5SY8114-8 — D-Curve MCB for High-Inrush Loads
The Siemens 5SY8114-8 is a 1-pole SENTRON miniature circuit breaker with a D tripping characteristic, rated for 400 V AC at 50/60 Hz. It delivers a 70 kA breaking capacity per IEC 60947-2 — the figure that governs fault clearance in industrial panels — and 15 kA DC for DC-side protection. Under UL 1077 it's listed at 5 kA, so it's accepted in North American supplementary protection roles as well.
What the Ratings Mean for Your Panel
The D curve means this breaker is built for loads with high inrush — motor starters, transformers, welding equipment, and DC power supplies. It tolerates a short-duration surge well above its rated current without nuisance tripping, then clears a hard fault at the full 70 kA. That 70 kA interrupting rating per IEC 60947-2 is the key number for panel coordination: it tells you this MCB can safely interrupt a fault up to that level without upstream devices needing to clear it first. Pollution degree 3 (conductive pollution or dry non-conductive with condensation) and overvoltage category III (fixed installation) confirm it's meant for the industrial distribution board, not a residential load center. Rated for ambient operation from -40 °C to 75 °C, with a derating curve above 55 °C (95 % RH at 55 °C, 55 % at 70 °C, 35 % at 75 °C). That matters if you're mounting it near a heat source or in a warm enclosure — the breaker's thermal trip element responds to ambient temperature, so you'll need to account for the reduced continuous current at the higher end of the range.
Panel Fit and Mounting
Occupies 1 modular width unit (18 mm) on a DIN rail. Installation depth is 70 mm; overall depth 76 mm, which includes the terminal projection. Mounting position any, fastening via the quick-assembly system — snaps onto the rail, no tools needed. Combined terminals top and bottom accept the supply from either side, so you can feed the busbar from the top or bottom without extra hardware. Sealable with a lead seal or adhesive label for tamper-proofing in metering or critical circuits.
Compliance and Documentation
Certified to IEC / EN 60947-2 and UL 1077 / CSA C22.2 No. 235. Halogen-free and silicon-free construction — relevant for clean-room or semiconductor-adjacent installations where outgassing must be controlled. Vibration tested per IEC 60068-2-6: ±1 mm at 5–25 Hz, 50 m/s² at 25–150 Hz. Mechanical service life 10 000 operating cycles typical. Supplementary devices (auxiliary switches, shunt trips, alarm contacts) can be installed on the side.