Unlisted nonconductive outside plant optical fiber cables are not permitted in which type of raceways?

Unlisted nonconductive outside plant optical fiber cables cannot be used in flexible metal conduit due to safety and performance standards established in the National Electrical Code (NEC). Flexible metal conduit is designed for an environment where grounding and bonding are essential, and it is typically used to provide mechanical protection for conductors in potentially hazardous areas.

Using nonconductive optical fiber cables in flexible metal conduit poses risks, as these cables are not designed to utilize the grounding features of the conduit, which can lead to issues with electromagnetic interference and signal degradation. Furthermore, the flexibility of the conduit may also not provide adequate protection against physical damage to nonconductive cables.

In contrast, rigid conduit, plastic conduit, and underground raceways have specific allowances under the NEC that can accommodate or protect different types of cables, including those that are unlisted as long as they meet certain installation standards and conditions. Therefore, the restrictions around using nonconductive outside plant optical fiber cables are particularly focused on flexible metal conduits due to their nature and application in electrical systems.