2N and N+x Redundant Configurations With the addition of an external redundancy module SDN™ Series, power supplies can be used in applications that require true redundant operation, including 2N and N+x configurations. All SDN units include built-in current sharing for parallel and redundant operation. All models ending in P also include a DC OK status relay contact. The external SDN 2.5-20RED and SDN 30/40RED modules increase reliability by isolating the supplies and adding more signal options. Paralleling for increased power does not require the use of these modules.