What the ratings mean for fit
The 5SL4120-0RC: The 20 A rating sets the continuous load limit — don't push past 20 A sustained on a single pole. The 10 kA breaking capacity means this breaker can safely interrupt a fault current up to 10,000 A at the rated voltage; that's standard for most commercial and light industrial panelboards fed by a typical distribution transformer. The Z characteristic is the key differentiator here: it's designed for circuits where the load current is steady but short-duration inrush is minimal — think control transformers, relay coils, PLC power supplies, and electronic ballasts. If you're protecting motor circuits or general-purpose socket outlets, a B or C curve is usually the better call.