What the ratings mean for fit
The Siemens 5SY4135-7 is a SENTRON 1-pole miniature circuit breaker with a C tripping characteristic and a 35 A rated current at 35 °C ambient. The C-curve means it trips between 5 and 10 times rated current — designed for inductive loads like motor starters and small transformers where inrush is higher than a resistive load. The 10 kA breaking capacity per EN 60898 covers standard domestic/commercial fault levels; the 15 kA per IEC 60947-2 extends its use to industrial panels where higher prospective short-circuit currents are expected. The DC rating of 15 kA per IEC 60947-2 also applies, so it handles DC side protection in rectified supplies or battery circuits.
Derating and ambient conditions
At 40 °C the 35 A rating derates to 33.32 A; at 50 °C it drops to 31.57 A; at 60 °C to 29.68 A. If the panel runs warm — say inside a non-ventilated enclosure near other heat sources — use the 40 °C or 50 °C column for sizing. The breaker is rated for pollution degree 3 (conductive pollution or dry non-conductive that becomes conductive through condensation) and overvoltage category III, which is the standard for fixed installations downstream of the main distribution board. Operating temperature range is -40 °C to 75 °C, so it works in unheated warehouses or outdoor cabinets as well as warm machine enclosures.
Mechanical fit and panel integration
At 18 mm width (one modular unit), the 5SY4135-7 snaps onto a standard DIN rail via the quick assembly system. Mounting position is any — horizontal, vertical, upside-down — no derating needed for orientation. Depth is 76 mm, installation depth 70 mm, so it clears most standard enclosures. The combined top and bottom terminals accept wiring from either direction, and the breaker is sealable for applications requiring tamper-evident locking. Touch protection is built in (IP20 with connected conductors). Halogen-free and silicon-free construction matters for environments sensitive to outgassing — clean rooms, semiconductor fabs, or food processing lines.