The Siemens 5SY3240-7 is a 2-pole SENTRON miniature circuit breaker rated 40 A at 400 V AC, with a C tripping characteristic — meaning it handles moderate inrush from motor or lighting loads without nuisance tripping, while still clearing short circuits fast. Breaking capacity is 4.5 kA per EN 60898 and 6 kA per IEC 60947-2, with a DC rating of 15 kA at 72 V (IEC 60947-2) and 5 kA under UL 1077 / CSA C22.2 No.235. That UL/CSA figure matters if the panel needs a recognized branch-circuit protector for North American acceptance. At 36 mm wide (2 width units), 90 mm tall, and 76 mm deep, it snaps onto a standard DIN rail via the quick-assembly system. Terminals accept 0.75 to 35 mm² solid or stranded copper — sized for the full 40 A load without needing to pigtail down to a smaller lug.
The breaker is halogen-free and silicon-free, rated for ambient temperatures from -25 °C to +55 °C, and can be stored from -40 °C to +75 °C. IP20 protection applies with conductors connected. Overvoltage category III and energy limiting class 3. It carries touch protection on the terminals.