#12 stranded wire gauge 3/8" four conductor black, white and green Chicago plenum wire assemblies For 1/2" knockouts are installed in “air plenum” ceilings to distribute power to lighting fixtures. The 6 ft. long corrugated steel tubing provides a sealed flexible raceway to prevent the penetration of air, vapor, and dust. Garvin Industries’ Chicago Plenum wiring assemblies create an “air tight” sealed wire raceway to prevent smoke from exiting box enclosures or conduits. The preassembled components cut labor hours significantly and enhances safety.