Code Change Summary: A new exception for flexible cords and flexible cables was added to note 5 under 400.12 (uses not permitted).

Section 400.10 now specifies the uses permitted for flexible cords and flexible cables while 400.12 provides the uses NOT permitted. These requirements were previously found in 400.7 and 400.8 of the 2014 NEC^®. More importantly, in the 2017 NEC^®, a new exception was added to note 5 under 400.12 (uses not permitted).

Note 5 states that flexible cables, flexible cord sets, and power supply cords shall not be used where “concealed by walls, floors, or ceilings or located above suspended or dropped ceilings”. The new exception now allows it, if contained within an enclosure for use in “Other Spaces Used for Environmental Air” as permitted by 300.22(C)(3).

When Section 300.22(C) speaks of “Other Spaces Used for Environmental Air” it means spaces not specifically fabricated for environmental air-handling purposes but used for air-handling purposes as a plenum.

Plenums sometimes exist in the space above a suspended ceiling where an air conditioner may be present.

Here are two rules to determine if the space above a grid ceiling is a plenum:

• If the above grid AC unit pulls return air from the office space below, through a dummy grill, instead of return air ductwork, then the return air circulates above ceiling where wiring methods also exist. This is a plenum.
• If the above grid AC unit pulls return air from the office space below, through a ducted return air grill, then the return air does not circulate among the wiring methods above ceiling. This is NOT a plenum.

Wiring methods permitted from 300.22(C) in a plenum are generally limited to metal cables, metal boxes, metal raceways and certain nonmetallic jacketed plenum rated cables with low smoke and heat release properties. The idea is to make sure that if an above ceiling cable melts, the smoke released back into the return air, and recirculated back into the building supply air system is not dense enough to block emergency lights and exit signs from being seen by building occupants during egress.

The new exception to 400.12(5) basically allows a flexible cord to be installed above a suspended ceiling as long as it is contained within an enclosure that is either made of metal or it can be nonmetallic as long as it is listed for use within plenum and has low smoke and heat release properties.

Below is a preview of Article 400. See the actual NEC^® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the 2017 NEC^® edition of NFPA 70.