The Siemens 3RU7126-1GB0 is a SIRIUS S0 thermal overload relay rated for a main circuit operational current of 6.3 A at 690 V, 50/60 Hz, with Trip Class 10 protection. It mounts directly onto a contactor of the same S0 frame size, making it a matched thermal protection element for motor starters in control panels.
The 6.3 A rated current sets the full-load motor current it protects — size the relay to the motor nameplate FLA, not the breaker. Trip Class 10 means it will trip within 10 seconds at 7.2× the current setting, which is the standard for standard-duty induction motors; a faster trip (Class 5) or slower (Class 20) would be needed for submersible or high-inertia loads respectively. Rated insulation voltage is 690 V AC with pollution degree 3, and surge voltage resistance is 6 kV — this covers 400 V and 480 V line-to-line systems with margin for transient spikes on industrial networks.
Fastens directly onto an S0 contactor (e.g. 3RT1016 or 3RT1015) — no DIN rail required, though the contactor itself may be rail-mounted. Side spacing to grounded parts must be at least 6 mm. 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) with ferrules. Auxiliary/control circuit terminals are also screw-type, torque 0.8…1.2 N·m. The front and terminal areas are IP20 rated — suitable for enclosed panels, not open washdown zones.