In situations where true redundant operations are mandatory, as with 2N and N+x configurations, this external redundancy model, the Sola HD from the SDN™ Series, is ideal. All the SDN units have a built-in current sharing technology allowing parallel and redundant operation. And in models ending in P, there is DC OK status relay contact too. The external SDN 2.5-20RED and SDN 30/40RED can isolate supply and add more signal options for improved reliability. These models are not needed to parallel for more power is needed.