What this MCB does and where it fits
The Siemens 5SY7120-6 is a 1-pole miniature circuit breaker from the SENTRON series, rated 400 V AC at 50/60 Hz with a B tripping characteristic. It snaps onto a DIN rail in any mounting position, occupying one modular width (18 mm). The B-curve trips between 3 and 5 times rated current — standard for protecting cable runs and general-purpose circuits in commercial and industrial panels where inrush is modest.
Breaking capacity and what it means for your panel
This breaker carries a 15 kA breaking capacity per EN 60898 and 25 kA per IEC 60947-2 at 400 V AC. The higher IEC figure means it can interrupt fault currents up to 25 kA under the industrial standard — useful for panels with high available fault current near a transformer. For DC circuits, it is rated 15 kA per IEC 60947-2. Under UL 1077 (supplementary protector listing) it holds 5 kA at 440 V AC multi-phase.
Environmental and installation details
Rated for ambient temperatures from -40 °C to 75 °C, with humidity derating above 55 °C. Degree of pollution 3 (conductive pollution, typical for industrial enclosures), overvoltage category III. IP20 with connected conductors — protected against finger contact but not water ingress, so it belongs inside a sealed panel. The housing is halogen-free and silicon-free. Top and bottom terminals accept combined wiring; the unit is sealable for tamper-proofing.