For underground service conductors, what type of conduit is not permitted as a raceway?

The correct choice is based on the requirements set by the National Electrical Code (NEC) regarding the installation of underground service conductors. Schedule 40 PVC conduit is not permitted as a raceway for underground service conductors under conditions that necessitate the protection that other types of conduit can provide.

Schedule 40 PVC conduit is generally used for above-ground applications where the environment is less hazardous. When it comes to underground applications, there are specific requirements for durability and resistance to environmental factors, including moisture and potential physical damage. Other types of conduit, such as rigid non-metallic or rigid metallic conduit, are designed to offer enhanced protection that is required for underground installations. This is crucial for maintaining safety standards and ensuring the longevity of the electrical system.

In summary, the prohibition of Schedule 40 PVC conduit in the context of underground service conductors stems from the need for robust protection against environmental challenges that underground installations face, aligning with the NEC regulations aimed at ensuring safe electrical practices.