The Siemens 5SY6604-8 is a SENTRON 5SY6 miniature circuit breaker rated 4 A with a D tripping characteristic, 4-pole (3P+N), for 400 V AC systems. The 4 A rating and D curve together suit it for small motor branch circuits or inductive loads where the starting surge exceeds the C-curve threshold. The 4-pole configuration with neutral switching (3P+N) means it disconnects all three phases and the neutral, which is required in some regional distribution schemes or for isolating a four-wire load. Rated 440 V AC for multi-phase operation, it covers standard 400/415 V three-phase networks. The 72 V DC maximum rating and 15 kA DC breaking capacity (IEC 60947-2) extend its use to DC control circuits or battery-backed supplies, though the primary application is AC branch protection.
The 72 mm width (4 width units) occupies four 18 mm module spaces; the 76 mm depth and 70 mm installation depth leave clearance for wiring behind the panel door. Any mounting position is permitted, so orientation within the enclosure is flexible.
Halogen-free and silicon-free construction reduces corrosive outgassing in sealed enclosures. Rated for ambient temperatures from -40 °C to 75 °C, with derating above 55 °C per the humidity curve (max 95% RH at 55 °C, tapering to 35% at 75 °C). Sealable to prevent tamper access. Touch protection is built in. Approvals include EN 60898 (6 kA), IEC 60947-2 (30 kA AC, 15 kA DC), and UL 1077 / CSA C22.2 No. 235 (5 kA AC) — covering European and North American installations.