Siemens Overload relay thermal for motor protection, 9 - 12.5AProduct Overview The Siemens 3RU2126 1KB0 is a thermal overload relay from the SIRIUS 3RU2 series, designed to protect three phase motors against overload, phase failure or phase asymmetry. It mounts onto compatible SIRIUS size S0 contactors, providing adjustable current protection and an integrated auxiliary contact block for signalling or control feedback. With adjustable current range and robust trip response, it helps safeguard motors and ensure