Which conductor size must be stranded when installed in raceways?

The requirement for stranded conductors is rooted in the need for flexibility in installations, especially in raceways where conductors may need to bend or maneuver to navigate around obstacles. While larger conductor sizes can remain rigid, smaller conductors benefit from being stranded as it allows them more versatility without risking damage to the wire insulation or conductor itself during installation.

For 8 AWG and larger sizes, the National Electrical Code (NEC) specifies that stranded conductors are often utilized to ensure they can be easily routed within raceways and still maintain their electrical and physical integrity. This practice also helps in reducing the risk of breakage, especially in tight spaces where rigid conductors would not easily accommodate bends and turns.

Using stranded conductors for this range provides the necessary flexibility while ensuring compliance with NEC guidelines for raceway installations.