Siemens Overload relay for motor protection, size S2, 28-40AProduct Overview The 3RU2136 4FB0 thermal overload relay is designed for current dependent protection of three phase motors and electrical loads against overload, phase asymmetry, and phase failure. This Size S2, Class 10 relay features an adjustable current range of 28 to 40 A and is optimized for direct mounting on Siemens 3RT203 size S2 contactors (3RT2035, 3RT2036, 3RT2037, and 3RT2038) to provide reliable motor protection for high power