Conductors installed in nonmetallic raceways run underground are permitted to be arranged as _______, installations.

For conductors installed in nonmetallic raceways running underground, the option stating "all of these" is supported by the fact that various arrangements for conductors can be utilized depending on the installation requirements and safety codes.

When conductors are arranged as neutral, they facilitate the return path for current in the electrical system. This is particularly important in balancing loads and ensuring proper system functioning.

Arranging conductors as grounded conductors is essential for safety; it provides a pathway for fault currents to safely dissipate, protecting both equipment and personnel from electrical hazards.

Lastly, positioning conductors in an isolated phase arrangement can be beneficial for certain applications, such as reducing inductive interference between circuits or enhancing system reliability.

Overall, the versatility of conductor arrangements in nonmetallic raceways allows for a variety of configurations that align with regulatory standards and electrical safety practices, justifying the inclusion of all these options as permissible for underground installations.