Polarity matters on DC — the supply cord position must consider polarity, so mark the line and load sides during installation.
The SENTRON 5SY5 series is the DC-optimized railway variant of Siemens' standard 5SY miniature breaker family. If your panel was originally specified around a 5SY4116-6CC (16 A AC-rated unit), the 5SY5101-6CC11 will not drop in without rewiring — the current rating and DC arc rating are different. The 5SY5101-6CC11 is its own animal, sized for 1 A DC auxiliary circuits, not a general-purpose AC replacement.
Ambient temperature range is -40 °C to +75 °C, with humidity limits of 95% RH up to 55 °C, derating to 35% RH at 75 °C. That -40 °C low end is important for cold-climate rail depots or outdoor wayside cabinets that see frost. This is the right characteristic for protecting semiconductor-fed DC loads — a C-curve would let a fault ride through too long and damage downstream rectifiers or IGBT gate drives.