What it is and what it does
The Siemens 5SL6640-7 is a 3P+N SENTRON miniature circuit breaker (MCB) rated 40 A at 400 V AC with a C-curve trip characteristic and 6 kA breaking capacity per IEC 60898 (also rated 6 kA per IEC 60947-2). The C-curve means it trips between 5 and 10 times rated current — standard for general-purpose loads like lighting, socket outlets, and small motor circuits where moderate inrush is expected. This is a 4-module-width unit (72 mm wide) that snaps onto DIN rail in any mounting position.
Thermal derating and ambient limits
Rated 40 A at 30 °C ambient, the 5SL6640-7 derates to 38.07 A at 40 °C and 34.97 A at 55 °C. If your panel runs hot — say a packed enclosure near a process line — size the upstream load so continuous current stays under the derated figure at the actual ambient. The operating range spans -40 °C to 75 °C, which covers outdoor cabinets in cold climates and warm electrical rooms.
Panel fit and integration
Snaps onto DIN rail; 72 mm wide (4 modular width units), 90 mm tall, 76 mm deep with 70 mm installation depth. The housing is halogen-free and silicon-free, which matters for clean-room or sensitive electronics environments. Sealable terminals (IP20 with connected conductors) allow lockout/tagout. Overvoltage category III and pollution degree 2 suit fixed-installation distribution boards.