Siemens 5SY4440-8FA – 40 A D-curve MCB for industrial panel protection
The Siemens 5SY4440-8FA is a 4-pole miniature circuit breaker from the SENTRON series, rated 40 A with a D tripping characteristic and a 10 kA breaking capacity at 400 V AC. Mounting snaps onto a DIN rail (quick assembly system per) in any orientation. The 4-pole (4P) form factor occupies 4 width units (72 mm) on the rail, with a depth of 76 mm and an installation depth of 70 mm behind the panel surface. Terminals accept 0.75–35 mm² solid or stranded copper, tightened to 3.5 N·m — suitable for incoming supply cables up to 35 mm² and outgoing branch circuits.
Voltage ratings and application boundaries
Maximum DC voltage is 72 V — this is not a DC-rated breaker for solar or battery strings at higher voltages. Overvoltage category III suits fixed-installation distribution boards. The breaker is sealable and touch-protected per IP20 with connected conductors, meaning it is safe for use in enclosed panels but not in wet or dusty environments without an outer enclosure.
Halogen-free and silicon-free construction.