What the ratings mean for fit
The 3RB1066-1LG0: The 300-630A range covers large motor loads — think 150-315 kW at 400V. Class 10 trip means it clears a stalled rotor within 10 seconds at 7.2x FLA, which is standard for standard-duty induction motors driving pumps, fans, and compressors. The MOD.S10/S12 designation indicates adjustable trip class settings, so you can dial it down to class 10 for faster protection on sensitive loads or up to class 30 for high-inertia starts. The mounting rails let you snap it onto a 3TF68 or 3TF69 contactor without extra brackets, keeping the panel footprint tight. If you're retrofitting into an existing cabinet, it also mounts standalone on a DIN rail or base plate.