Primary distribution box: three-phase power supply, ground wire and zero wire are introduced from the transformer. Electrical equipment is installed under the switch box, forming a three-level distribution. "Two level protection" mainly refers to the use of leakage protection measures. Certification at each CMMC level occurs. The purpose of a PDS is to protect unencrypted national security information (NSI) that is transmitted via wire line or optical fiber. The Committee on National Security Systems (CNSS) issues this Instruction pursuant to its authority under National Security Directive 42, National Policy for the Security of National Security Telecommunications and Information Systems. This Instruction provides guidance and requirements for the. Further distribution only as directed by [controlling DoD office] [date of determination] or higher DoD authority. Information has been predetermined by the DoD controlling agency, in accordance with established foreign disclosure policies, to be releasable through established foreign.