What this MCB does on the rail
The Siemens 5SY8516-8 is a 2-pole (1P+N) SENTRON miniature circuit breaker with a D tripping characteristic, rated 16 A at 50/60 Hz. The D-curve means it tolerates high inrush currents — think motor starts, transformer energization, or welding equipment — without nuisance tripping, while still clearing a hard fault. Breaking capacity sits at 30 kA per IEC 60947-2, so it handles substantial fault currents in an industrial panel without needing an upstream current-limiting device. At 36 mm wide (2 modular units), it snaps onto a standard DIN rail in any mounting position. Depth is 76 mm, installation depth 70 mm — factor that into gland-plate clearance if you're packing a shallow enclosure. Rated for overvoltage category III, pollution degree 3, so it's comfortable in a typical control cabinet environment, not just a clean residential load center.
Temperature derating — the real-world numbers
The 16 A rating holds at 45 °C. At 50 °C it drops to 15.5 A, and at 55 °C it's 14.99 A. If your panel runs hot — say, a packed cabinet with drives below — use the 55 °C figure for sizing. Ambient range is -40 °C to 75 °C, so cold-storage lines or outdoor cabinets are fine.
DC and UL ratings — not just an IEC part
DC breaking capacity per IEC 60947-2 is 15 kA, which matters if you're protecting DC bus feeds or battery circuits. Under UL 1077 and CSA C22.2 No. 235 it's rated 5 kA — useful for North American supplementary protection applications. That dual rating saves you from stocking a separate UL-listed breaker for export panels.