What is the maximum size conductor that is generally permitted to be a solid conductor where installed in a raceway?

10 AWG

Explanation:

AWG is American Wire Gauge Standard. This is a standardized wire gauge system for the diameters of round, solid, nonferrous, electrically conducting wire.

Due to the high resistivity, small area (0.9989 ohms/1000ft and high frequency about 2600 Hz, 100% skin depth), and flexibility of 10 AWG, it is used in raceway. Raceway is is an enclosed conduit that forms a physical pathway for electrical wiring. Raceways protect wires and cables from heat, water intrusion and general physical threats.