What is considered a plenum?

In building construction Plenum is a separate space provided for air circulation for heating, ventilation, and air-conditioning. It is commonly found in the space between the structural ceiling and a drop-down ceiling or under a raised floor.

Which of the following are permitted to be used in a plenum?

Wiring methods 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.

What is considered environmental air?

Environmental air is air that is supplied, returned, re-circulated, or exhausted from spaces for the purpose of modifying the existing atmosphere within the building.

Is EMT conduit plenum rated?

Electrical metallic tubing (EMT), rigid metal conduit (RMC), intermediate metal conduit (IMC), armored cable, metal-clad (MC) cable without a nonmetallic cover, and flexible metal conduit (FMC) can be installed in a cavity plenum space.

Where can I find NFPA 300.22 ( C )?

Once there, click on the “free access” tab and select the applicable year of NFPA 70 (National Electrical code). 300.22 (C) (1) Wiring Methods.

What are the requirements of section 300-22 ( B )?

Section 300-22 (b) provides requirements for ducts or plenums used for environmental air. These ducts or plenums, such as metal or fiberglass ducts, are those specifically fabricated to transport environmental air. These ducts can be either fabricated at the site or brought in pre-fabricated and assembled at the site.

What is an exception to NEC 300.22 ( B )?

Code Change Summary: A new exception was added to address wiring methods allowed in ducts specifically fabricated for environmental air-handling purposes. In NEC 300.22 (B), wiring methods are only permitted within ductwork (containing environmental air) if necessary for the direct action upon, or sensing of, the air contained inside the duct.

What does NFPA 90A say about air ducts?

NFPA 90A defines “duct” or “air duct” as “a conduit or passageway for conveying air to or from heating, cooling, air conditioning, or ventilating equipment but not including a plenum.” Easy? Not exactly. Determining the wiring methods permitted in these areas would be difficult at best, if not for the NEC.