Siemens SITOP Redundancy Module 6EP1961-3BA20 combines the outputs of two 24 V DC power supplies into a single redundant feed. It's the standard decoupling device for a 24 V DC bus that needs to stay up if one supply fails. Listed under PLC expansion modules, but its job is power rail reliability, not logic expansion. You mount it between the power supplies and the load, same as a diode OR-ing module.
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Combines the outputs of two 24 V DC power supplies into a redundant bus. For full electrical ratings, consult the Siemens datasheet.