What it is and what it does
The Siemens 5SJ4135-8HG40 is a SENTRON miniature circuit breaker from the 5SJ4 series, designed for branch-circuit protection in industrial control panels. It is a single-pole unit rated 35 A at 30 °C and 40 °C, with a D tripping characteristic that handles inrush currents from motor starters and transformers without nuisance tripping. The breaker also carries a DC rating of 60 V maximum, making it suitable for DC control circuits common in automation panels.
Key ratings and what they mean for fit
The D-curve (tripping characteristic D) means the magnetic trip operates at 10 to 20 times the rated current — 350 to 700 A for this 35 A unit. That suits loads with high starting surges, such as small motors, solenoid valves, or transformer primaries, where a B- or C-curve would trip on inrush. The 35 A rating holds at 30 °C and 40 °C; at 45 °C it derates to 34 A, at 50 °C to 32.9 A, at 55 °C to 31.8 A, and at 60 °C to 30.8 A. If the panel ambient runs above 40 °C, the continuous load must be reduced accordingly. The DC rating of 60 V maximum applies per pole. In a 24 VDC control circuit, this breaker provides overcurrent protection without needing a separate DC-rated fuse. The AC/DC voltage type means it can be used on either supply, but the 60 V DC ceiling is the binding limit for DC applications.
Environmental and compliance
Rated for ambient temperatures from -40 °C to 75 °C, covering most industrial enclosures. Protection class is IP20 with connected conductors, IP40 in the handle area — suitable for dry indoor panels but not washdown zones. Degree of pollution 3 and overvoltage category 3 indicate it is designed for industrial environments with conductive pollution and transient overvoltages. Vibration resistance is 50 m/s² at 25 to 150 Hz and 60 m/s² at 35 Hz (4 seconds). The breaker is halogen-free and silicon-free, which matters for applications sensitive to outgassing, such as clean rooms or sealed enclosures with electronics.