What size conductors must be stranded when installed in raceways?

When considering the installation of conductors in raceways, it's important to note that stranded conductors are generally required for larger gauge sizes. In this case, the correct choice is 14 AWG, as it is permissible for copper conductors of 12 AWG and smaller to be solid or stranded, while 14 AWG usually adheres to the stranded requirement due to ease of installation in confined spaces with bends or when pulling through conduits.

Larger sizes such as 10 AWG, 8 AWG, and 6 AWG typically need to be stranded to provide flexibility, which is crucial when navigating bends in raceways or dealing with movement, preventing the risk of breakage that may occur with solid conductors.

The characteristics of the smaller size make stranded conductors more advantageous in certain scenarios, making 14 AWG a suitable answer in this context.