The Siemens 3RB1066-2KG0 is a solid-state overload relay from the 3RB10 series, rated 200-540 A with a class 20 trip curve. It is designed for motor protection in industrial control panels, providing thermal overload protection for three-phase induction motors. The relay includes mounting rails for direct attachment to 3RT106 contactors or for separate DIN-rail mounting, giving flexibility in panel layout.
What the ratings mean for fit
The 200-540 A current range covers medium-to-large motor loads — think 90 kW to 250 kW at 400 VAC, depending on motor full-load current. The class 20 trip curve means the relay allows 20 seconds of locked-rotor current before tripping, matching NEMA design B and C motor starting characteristics. This is the standard protection class for general-purpose industrial motors driving pumps, fans, and compressors. The solid-state design means no bimetal aging drift, consistent trip accuracy over the relay's service life, and no ambient-temperature compensation issues within the rated range. It also provides a wider adjustment bandwidth than a thermal bimetallic relay of the same frame size.
Mounting and integration
The relay ships with mounting rails for direct attachment to 3RT106 contactors — this is the intended use for a compact motor starter assembly. For panel layouts where the overload relay sits remote from the contactor, the same rails support separate DIN-rail mounting. The MOD.S10/S12 designation indicates the mechanical interface and terminal arrangement; verify the contactor frame size matches before committing the BOM line.