What it is and what it does
The Siemens 5SJ4135-7HG40 is a SENTRON 5SJ4 series miniature circuit breaker, 1-pole, with a C tripping characteristic. It's rated 35 A at 400 V AC and carries a DC rating up to 60 V. The C-curve means it trips between 5 and 10 times rated current — standard for protecting inductive loads like motor starters and contactor coils in control panels.
Key ratings and what they mean for fit
The 35 A rating holds at 30 °C and 40 °C, then derates: 34 A at 45 °C, 32.9 A at 50 °C, 31.8 A at 55 °C, and 30.8 A at 60 °C (–). If your panel ambient runs above 40 °C, you need to account for that drop — especially in a sealed enclosure. The 18 mm width takes one modular unit on a standard DIN rail, so it fits tight layouts. Pollution degree 3 and overvoltage category 3 mean it's rated for industrial environments with conductive pollution and transient overvoltages up to 4 kV.
Where it's used
This MCB is designed for mechanical engineering and industrial applications. It's a standard branch-circuit protector for control transformers, solenoid valves, and small motor loads in panels where the C-curve prevents nuisance tripping on inrush. The IP20 rating is fine inside a closed panel; the handle area is IP40.