What this relay does in the panel
The Siemens 3RU5156-2HB2 is a SIRIUS thermal overload relay sized for motor protection in the 55-80 A range, Class 10 trip curve. The 55-80 A window means it catches the full-load current of a motor in that band; the Class 10 trip gives you a 10-second maximum lock-rotor time before the bimetals open the auxiliary contact. That matters when you're coordinating with a contactor that can handle a 7x inrush for a few seconds but not a sustained stall.
Size S6 — what the frame means for integration
Size S6 is the physical frame — this is a larger relay, not a compact S00 or S0. It mounts standalone (single mounting) with screw terminals. The 55-80 A range and S6 body pair naturally with a contactor in the same frame class, typically the Siemens 3RT106 or similar S6 contactor. Panel space is the constraint: the S6 footprint is wider and deeper than the smaller sizes, so verify the DIN rail or backplate layout before committing the BOM. The manual/automatic reset selector on the front gives the commissioning engineer a choice — manual for troubleshooting, auto for unattended restart.
Electrical environment — surge and frequency
Rated surge voltage resistance is 8 kV, which puts it in the typical industrial panel category for 400/480 V systems — it handles switching transients from contactor coils and nearby VFDs without flashover. Operating frequency is 50-60 Hz, so it's agnostic between 50 Hz European and 60 Hz North American line frequencies.