What this breaker is and where it fits
The Siemens 5SY4218-7 is a 2-pole miniature circuit breaker from the SENTRON family, designed for DIN-rail mounting in distribution panels and industrial control enclosures. It's a C-curve device — meaning it trips at 5 to 10 times rated current, which is the standard choice for motor circuits and moderate inrush loads where you need some short-term overload tolerance without losing the short-circuit protection.
Breaking capacity and what it means on your line
This breaker carries a 10 kA interrupting rating per IEC/EN 60898-1, and 20 kA per IEC 60947-2 at 400 V AC. That 20 kA figure is the one that matters for industrial panel coordination — it tells you this MCB can safely clear a fault up to 20 kA without welding its contacts or blowing apart, which gives you headroom for most secondary distribution panels fed by a transformer. For DC circuits, it's rated 15 kA at 60 V (72 V max) per IEC 60947-2, and under UL 1077 it's listed for 5 kA. The dual rating means it's built for IEC-spec panels globally but also carries the UL mark for North American machinery control panels.
Panel fit and environmental tolerance
The 5SY4218-7 occupies 2 modular width units (36 mm) on a DIN rail, with a depth of 76 mm and an installation depth of 70 mm. It mounts in any position, and the terminals accept top and bottom comb busbars for easy distribution. The housing is halogen-free and silicon-free — important if this panel sits near sensitive electronics or in a clean-room boundary. Temperature range runs from -40 °C to 75 °C, with humidity derating above 55 °C (95% at 55 °C, down to 35% at 75 °C). That covers most plant-floor environments, including unheated warehouses and outdoor-rated enclosures. IP20 with conductors connected — standard for inside a closed panel.