What it is and what the ratings mean
The Siemens SENTRON 5SY7402-8 is a 4-pole miniature circuit breaker with a D tripping characteristic, rated 2 A at 35 °C. The D curve means it tolerates inrush currents 10–20 times the rated current — designed for motor and transformer branch circuits where the starting surge would nuisance-trip a B or C curve. Breaking capacity is 15 kA per EN 60898 and 50 kA per IEC 60947-2, so it clears faults up to that level without cascading upstream. The 4-pole (4P) configuration switches all three phases plus neutral, common in three-phase panelboards where neutral isolation is required.
Deployment context and integration
Mounts in any position on a DIN rail via the quick-assembly system. At 4 modular width units (72 mm wide), it occupies standard panel space. Combined terminals top and bottom accept conductors; IP20 with connected conductors means it's protected against finger contact once wired. Pollution degree 3 and overvoltage category III suit it for industrial control panels and distribution boards where conductive dust and transient overvoltages are present. Rated for 50/60 Hz supply.
Thermal derating and ambient limits
The 2 A rating holds at 35 °C. Above that, derate linearly: 1.9 A at 40 °C, 1.85 A at 45 °C, 1.8 A at 50 °C, 1.75 A at 55 °C, and 1.7 A at 60 °C. Operating ambient range is -40 °C to 75 °C. Humidity derating applies: max 95% RH up to 55 °C, then 55% RH up to 70 °C, then 35% RH up to 75 °C. If the panel runs hot, size the load accordingly.