The Siemens 5SY8604-8 is a 4-pole (3P+N) miniature circuit breaker from the SENTRON series, with a D tripping characteristic rated at 4 A and a 50 kA breaking capacity at 400 V AC per IEC 60947-2. That D curve means it handles high inrush currents — think motor starts, transformer energization, or industrial lighting banks — without nuisance tripping on the magnetizing spike, while still clearing a hard fault at 50 kA.
Ratings that matter for the panel
Under UL 1077 and CSA C22.2 No. 235, the interrupting rating is 5 kA, so if the panel is built to North American supplementary-protector rules, that's the figure to use for coordination. At DC per IEC 60947-2, it's rated 15 kA. The D characteristic means the magnetic trip fires at 10 to 20 times In (40 to 80 A for this 4 A unit). That's the right choice for loads with a high starting surge — a small motor, a solenoid bank, or a control transformer. The thermal element handles overloads on a slower curve, so a momentary inrush won't drop the load. Temperature derating is published: 4 A at 45 °C, 3.9 A at 50 °C, 3.8 A at 55 °C. If the panel runs hot, factor that in.
Integration notes
The combined terminal at top and bottom accepts both busbar and conductor, which speeds up daisy-chaining in a multi-pole distribution block. Touch protection is provided with connected conductors, and the unit is sealable for tamper-proofing after commissioning.