The Siemens 3RU2126-4CB0-Z W97 is a thermal overload relay rated 17-22 A, Class 10, in frame size S0. It mounts directly onto Siemens contactors and provides motor protection against overload conditions. The relay supports manual or automatic reset, selectable on the unit, which is useful for remotely monitored lines where you want automatic restart after a fault clears.
Frame size S0 is the standard Siemens footprint for contactors and overloads up to about 32 A. The 3RU2126-4CB0-Z W97 clips directly onto the matching S0 contactor — no wiring between contactor and overload beyond the power connections. This keeps the DIN-rail assembly compact and the wiring clean. The unit ships in multi-unit packaging of 16 pieces, which is worth noting if you're stocking spares for a line — order in that quantity to keep packaging consistent.
RoHS compliance is confirmed since October 2009. REACH candidate list information is available per Article 33. Export control is straightforward: AL N / ECCN N, so no special licensing for cross-border shipments.