What it is and what it does
The Siemens SENTRON 5SJ4135-7HG42 is a 1-pole miniature circuit breaker (MCB) from the 5SJ4 series, designed for branch-circuit protection in industrial control panels and distribution boards. Its C-curve tripping characteristic (5–10× In) makes it a standard choice for moderate inrush loads like motor starters and small transformers — it holds through the start surge but trips fast on a hard short. Rated 35 A at both 30 °C and 40 °C ambient, it derates to 30.8 A at 60 °C — a 12% drop that matters if the breaker lands in a hot cabinet next to drives or transformers. The 10 kA breaking capacity per EN 60898 is enough for most secondary distribution panels fed by a 100 kVA or smaller transformer; for higher fault current panels (e.g., near a 630 kVA unit), you'd step up to a 15 or 25 kA rated MCB. The part is sealable, halogen-free, and silicon-free — useful in food, pharma, or semiconductor fabs where outgassing or contamination risk is a concern. It mounts on standard DIN rail in any position and occupies a single modular width (18 mm), so it fits a standard 18 mm pitch panel without crowding.
Physical fit and installation
Dimensions: 18 mm wide, 121 mm tall, 70 mm deep. The 70 mm depth includes the body and the terminal area — it sits flush in a standard 70 mm deep distribution board. Combined terminals top and bottom accept Cu conductors; tighten to 3.5 Nm. Protection class is IP20 with conductors connected, IP40 in the handle area — fine for enclosed panels, not for washdown zones without an enclosure. Vibration resistance is rated at 50 m/s² over 25–150 Hz and 60 m/s² at 35 Hz (4 sec) — sufficient for machine-mounted panels on pumps, conveyors, or compressors. Overvoltage category 3 and pollution degree 3 mean it's rated for fixed installations in industrial environments where transient overvoltages and conductive dust are expected.