Which single conductor in an AC system is permitted to be installed by itself in a metallic raceway?

In an AC system, the grounding electrode conductor is specifically permitted to be installed by itself in a metallic raceway. This is largely due to the function and importance of the grounding electrode conductor, which is responsible for connecting the electrical system to the ground to ensure safety and protect against shock hazards.

The grounding electrode conductor serves as a crucial safety feature, helping to dissipate electrical faults safely into the ground. Its installation within a metallic raceway can help to provide additional physical protection and enhance its effectiveness. Additionally, this arrangement minimizes the risk of interference and ensures that this conductor can perform its role without being affected by other electrical components.

Other conductors, such as hot, neutral, and service entrance conductors, generally require different installation practices due to the specific electrical characteristics and the potential safety issues associated with carrying current. Regulations typically dictate their installation together with others of their kind or within particular configurations in the raceway to prevent hazards like electromagnetic interference or overloading. Thus, the grounding electrode conductor having the unique allowance underlines its fundamental role in electrical safety protocols.