D-curve 15 A — what the ratings mean for the panel
The 5SJ4318-8HG42 is a 3-pole miniature circuit breaker from the Siemens SENTRON 5SJ4 family, with a D tripping characteristic and a 15 A continuous rating. The D-curve (10–20× In magnetic trip) is designed for loads with high inrush current — motor starters, small drives, transformers, or welding equipment — where a B or C curve would nuisance-trip on startup. It carries dual interrupting ratings: 10 kA per UL 489 at 480Y/277 V, and 15 kA per IEC 60947-2 at 400 V AC. For a panel built to UL 508A, the 10 kA SCCR at 277/480 V is the number that governs the branch-circuit protection — make sure the upstream fault current doesn't exceed that ceiling.
Mounting and fit — DIN rail, 3-module width
Snaps onto standard 35 mm DIN rail (EN 60715). Width is 54 mm (3 modular units at 18 mm each), depth 70 mm, height 121 mm. The 70 mm installation depth leaves room in a shallow enclosure — typical 80 mm deep panels clear it with 10 mm to spare.
Environmental range and approvals
Ambient operating range is -40 °C to +75 °C with up to 95 % humidity — wide enough for unheated warehouses, outdoor enclosures, or plant floors near ovens. Protection is IP20 with conductors connected, IP40 in the handle area; not rated for washdown or wet locations. Overvoltage category III, pollution degree 3 — suited for fixed installations in industrial environments where transient overvoltages and conductive dust are present. Vibration resistance tested at 50 m/s² (25–150 Hz) and 60 m/s² at 35 Hz.