The Siemens 3RU6126-4NB0 is a SIRIUS-brand thermal overload relay for motor protection. It mounts onto a size S0 contactor and provides adjustable overcurrent protection from 23 A to 28 A, with CLASS 10 trip characteristic.
Rated operational current is 28 A, adjustable range 23...28 A. The 3-pole design handles three-phase circuits up to 690 V at 50...60 Hz. CLASS 10 trip class is for standard motor starts. Power dissipation is 3.2 W per pole, totaling 7.1 W typical, and 9.6 W at rated current in hot operating state. That matters for thermal budgeting inside a closed panel — especially if multiple relays are ganged.
Fastens directly onto a size S0 contactor via the contactor mounting method. Mounting position is any orientation. Main circuit terminals are screw-type, top and bottom, accepting 2× (0.5...1.5 mm²) solid/stranded or 2× (0.75...2.5 mm²) — AWG equivalents 2× (16...12) and 2× (14...8). Auxiliary circuit terminals are also screw-type, accepting 2× (20...16) and 2× (18...14) AWG. Tightening torque for main contacts is 2...2.5 N·m. Side spacing to grounded parts must be at least 6 mm.