The Siemens 5SY8540-8 is a SENTRON miniature circuit breaker (MCB) with a D tripping characteristic, rated 40 A at 230/400 V AC, and a 25 kA breaking capacity per IEC 60947-2. This is a 2-pole (1P+N) unit with neutral switching, so it opens both phase and neutral on a fault. That matters in applications where the neutral must be positively isolated — not just switched — for maintenance or safety.
Deployment context and environmental limits
Vibration resistance per IEC 60068-2-6 (±1 mm at 5–25 Hz, 50 m/s² at 25–150 Hz) confirms it survives on machinery or in mobile equipment. The sealable design allows a lock or tag to prevent unauthorized operation — useful for lockout/tagout programs.
Integration: what fits where
Any mounting position is permitted.
Temperature derating — the number that matters for real loads
At 40 °C the breaker carries its full 40 A. At 50 °C it derates to 38.76 A; at 55 °C to 37.48 A. The humidity limits (95% at 55 °C, 55% at 70 °C, 35% at 75 °C) are typical for indoor industrial environments; condensation is not expected.