The Siemens SIRIUS 3RU5156-3JB2 is a thermal overload relay sized for motor protection in the 110-135 A range, Class 10 trip curve. It sits between the contactor and the motor in a standard three-phase motor starter assembly, monitoring current draw and tripping on sustained overload before the motor windings overheat.
The adjustable current response value of 1.1 A is the threshold at which the bimetallic strip begins to deflect — set it to match the motor nameplate full-load current. The 8 kV surge voltage resistance ensures the relay withstands switching transients common in industrial power distribution without nuisance tripping or insulation breakdown.
Size S6 means this relay mounts to a Siemens S6 contactor or directly to a DIN rail via the screw-and-snap-on method. Manual or automatic reset is selectable, which matters for unattended installations where you want automatic restart after a trip, versus a manual reset for safety-critical lines. The auxiliary circuit terminals carry the trip and alarm signals back to the PLC or control relay.