The Siemens 5SL6420-7BB is a SENTRON miniature circuit breaker (MCB) in a 4-pole (4P) configuration, C-curve tripping characteristic, rated 20 A at 400 V AC.
Current production — no phase-out notice on record. The 5SL6 series is Siemens' standard residential/infrastructure MCB line, widely specified across Europe and Asia. For a BOM freeze, this part is stable; no PCN or LTB expected in the near term.
The breaker does not switch the neutral (4P without neutral switching), so it's a straight 4-pole overcurrent protection device for three-phase loads where the neutral is solidly connected. Temperature derating is published: 18.94 A at 40 °C, 18.4 A at 45 °C, 17.24 A at 55 °C — factor that into the panel thermal design if the breaker is in a warm cabinet.