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What is Flexible Metal Tubing - Article 360

Plen-Flex® is a smoketight, liquidtight Flexible Metal Tubing and is listed for use in plenums and other air handling spaces. Often referred to as FMT.

Plen-Flex® is constructed from a steel strip which contains an extra coating of zinc galvanizing for added protection against corrosion. This strip is formed into a corrugated profile and is tightly interlocked to form a smoketight, airtight, and liquidtight pliable tube, which weighs about 40% less than FMC (Greenfield).

This tubing is used to wire drop-in lighting fixtures and other equipment found in plenum ceilings and other air handling areas. Because it is smoke-tight when installed with sealing fittings and gasketed junction boxes, it would prevent smoke and other products of combustion from escaping out off the raceway and into air handling areas in the event of an electrical fire.

There is also no plastic jacketing material, which might give off toxic gases or burn. The fact that the system is liquidtight means that it will not allow the entrance of moisture from sprinkler systems into its interior. It is intended to be installed in accordance with Article 360 of the NEC® (ANSI/NFPA-70).

  • Listed for containment of 1000 volts and lower potential circuits.
  • For use in dry locations.
  • In accessible locations when protected from physical damage or concealed, such as above suspended ceilings. See Article 300.22(c).
  • In branch circuits.
  • Listed for grounding per Article 250.118(8)
  • Limited to six-foot lengths. Article 360.12(6)

Listed - File #E80694, Approved for use by the city of Chicago.

® Electri-Flex Company 1-800-323-6174,


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