What this 2-pole B-curve 20 A MCB is for
The Siemens 5SJ6220-6 is a SENTRON 5SJ6 miniature circuit breaker rated 20 A at 400 V AC with a B tripping characteristic and 6 kA breaking capacity per both EN 60898 and IEC 60947-2. It's a 2-pole unit that snaps onto a DIN rail — standard panel-mount for branch-circuit protection in distribution boards. At 20 A and 400 V line-to-line, it handles a single-phase or two-pole load in a 230/400 V system.
On a 230/400 V three-phase panel, a 2-pole breaker like this feeds a 400 V single-phase load or a 230 V load with both poles switched. The B-curve (3-5x In) is the right choice for resistive loads, lighting, and general wiring — it clears a short circuit fast but won't nuisance-trip on a brief motor start like a C-curve would. The DC rating maxes out at 60 V, so it's usable on low-voltage DC control circuits but not for 110 V DC battery banks.
Installation depth is 70 mm, and it occupies 2 width units (roughly 36 mm) in the panel. The breaker is sealable, which matters for panel builders who need to lock settings after commissioning. Ambient temperature range is -20 to +45 °C, with periodic excursions to +55 °C and up to 95% humidity. Vibration resistance is rated at 50 m/s² from 25 to 150 Hz and 60 m/s² from 10 to 150 Hz per IEC 60068-2-6 — it'll hold up on a machine skid or in a panel near rotating equipment.