Part identity and key ratings
The Siemens 5SL4420-8 is a SENTRON miniature circuit breaker (MCB) — 4-pole, D-curve, rated 20 A at 30 °C, with a 10 kA breaking capacity per both EN 60898 and IEC 60947-2 at 400 V AC. That 10 kA SCCR means it can safely interrupt a fault current up to that level without upstream damage in a residential or light-commercial distribution board. The D-curve (10–20× In magnetic trip) is sized for loads with high inrush — motor starters, small transformers, or lighting ballasts.
Thermal derating and operating envelope
Rated current is temperature-dependent: 20 A at 30 °C, 18.48 A at 40 °C, 17.6 A at 45 °C, and 15.92 A at 55 °C. If the panel ambient runs hot, size up one frame or account for the derated figure — the breaker won't hold its 20 A label above 30 °C. Operating temperature range spans -40 °C to 75 °C, with storage exceeding that — the low end matters for unheated enclosures in northern climates. Pollution degree 2 and overvoltage category III suit fixed-installation distribution boards.
Mounting and integration
Snap-on DIN rail mount, 4 modular width units (72 mm wide), 76 mm depth, 90 mm height. Installation depth is 70 mm — verify enclosure depth clearance before panel layout. Mounting position any, so vertical or horizontal busbars both work. IP20 with connected conductors — protected against finger contact but not washdown. Sealable, halogen-free, silicon-free construction. Touch protection integrated on the line-side terminals.