300.22 (B)

[warmfuzzy]

NEC 70 2005 states:
(B) Ducts or Plenums used for Environmental Air. Only wiring methods consisting of Type MI cable, Type MC Cable employing a smooth or corrugated impervious metal sheath without an overall nonmetallic covering, electrical tubing, flexible metallic tubing, intermediate metal conduit, or rigid metal conduit without an overall nonmetallic covering shall be installed in ducts or plenums specifically fabricated to transport environmental air. Flexible metal conduit and liquidtight flexible metal conduit shall be permitted, in lengths not to exceed 1.2 m (4 ft), to connect physically adjustable equipment and devices permitted to be in these ducts and plenum chambers.The conductors .....

I have a need to extend single phase branch power (120 or 208) from a NEMA box located under a raised floor, that is designed as a plenum to deliver environmental air, to a NEMA junction box located above the raised floor. I would like to use a flexible metal conduit to provide a wire pathway between the two NEMA boxes (one in the plenum, the other above the floor). My interpretation of Article 300.22 (B) is this is permitted as long as the flexible metal conduit or liquidtight does not exceed the 1.2 m (4 ft) limitation addressed above. Can anyone comment on my interpretation of the code in this situation.

[ron]

If this is a computer room type raised floor, and the room is not utilizing the leniencies in 645, then the area below the raised floor would be "other space used of environmental air" 300.22(C). The flex would be fine.

[ December 20, 2005, 01:29 PM: Message edited by: ron ]

[warmfuzzy]

Thanks Ron. Yes, this is a computer room that does not meet the 645 exemptions. So we follow the more restrictive NEC requirements in Article 300.

Regards