Editing Protective distribution system (section)

===Hardened carrier===
In a hardened carrier PDS, the data cables are installed in a carrier constructed of electrical metallic tubing ([[Electrical conduit|EMT]]), ferrous conduit or pipe, or rigid sheet steel ducting. All of the connections in a Hardened Carrier System are permanently sealed completely around all surfaces with welds, epoxy or other such sealants. If the hardened carrier is buried under ground, to secure cables running between buildings for example, the carrier containing the cables is encased in concrete.

With a hardened [[carrier system]], detection is accomplished via human inspections that are required to be performed periodically. Therefore, hardened carriers are installed below ceilings or above flooring so they can be visually inspected to ensure that no intrusions have occurred. These periodic [[visual inspection]]s (PVIs) occur at a frequency dependent upon the level of threat to the environment, the security classification of the data, and the access control to the area.