What the Z characteristic means for your circuit
The Siemens 5SL4240-0RC is a 40 A, 2-pole miniature circuit breaker from the Betagard family, carrying a Z tripping characteristic. That Z curve is the key spec here — it trips between 2 and 3 times rated current, which is tighter than a B curve (3–5× In) and much tighter than C or D. For a sourcing decision, the Z characteristic means this breaker is designed to protect sensitive electronic loads — PLC power supplies, control transformers, instrumentation loops — where a standard breaker might let through enough fault energy to damage downstream semiconductors. The 10 kA breaking capacity holds per both IEC 60898 and IEC 60947-2, so it's rated for the full fault duty in a typical 415 V AC panel without cascading upstream.
Temperature derating and environment
The 40 A rating holds at 50 °C ambient. Above that, derate: 39.1 A at 55 °C, 38.1 A at 60 °C. At 30 °C the breaker can carry 43.6 A continuous. Operating range spans -40 °C to 75 °C, with pollution degree 3 and overvoltage category III — standard for fixed industrial panels. Vibration resistance tested to 50 m/s² at 25 to 150 Hz per IEC 60068-2-6. IP20 with connected conductors, so it's panel-mount only, not for wet locations.
Physical fit and panel integration
Mounts on standard DIN rail in any position. Depth is 76 mm, height 90 mm, width 36 mm (2 modular units). Installation depth is 70 mm. Sealable, halogen-free, silicon-free construction. The 36 mm width matches standard 2-pole MCB footprint — drops into any panel designed for that form factor without rewiring.