The Siemens 3RU5156-2WB2 is a SIRIUS thermal overload relay for motor protection in the 63-90 A range, Size S6, Trip Class 10. It protects a three-phase motor by monitoring current through the main circuit and tripping when an overload condition persists beyond the Class 10 curve. The 3-pole design matches three-phase motor circuits. The 8 kV surge voltage resistance means the relay's insulation withstands transient overvoltages common in industrial power distribution — a useful margin when the relay sits downstream of a contactor in a motor control center. Operating frequency is rated 50-60 Hz, covering standard line frequencies worldwide.
The auxiliary circuit uses screw terminals for the trip/alarm signal wiring. Manual or automatic reset is selectable on the device, which is typical for thermal overload relays: manual reset forces an operator check after a trip, automatic reset suits remote or unattended installations. The relay is designed for the SIRIUS system, so it mechanically interlocks with the matching S6 contactor (3RT5 series) for a combined motor starter assembly.