Installing access points in the Plenum Space

By Oberon posted Nov 14, 2011 06:21 PM


This article describes code compliance when installing access points and cabling in suspended ceilings.


Facilities operators of commercial properties, particularly hospitals, public buildings, and federal buildings are strict adherents to National Fire Protection Association’s National Electric Code (NEC). Data network installers are keenly aware of the NEC due to the requirements for type and rating of cabling, fire-stopping, grounding, wire trays, etc. Of particular concern is installation of cabling in the air-handling (plenum) space. Due to the critical role of the air-handling space in fire suppression and containment, installers are diligent in observing NEC rules, and Authorities Having Jurisdiction (AHJs) are aggressive in enforcement of these rules.


Although wireless networks promise to reduce the total number of home run cables, the wireless infrastructure still requires cabling to be run to the wireless access point, and by virtue of the fact that the ideal location for wireless access points is in the ceiling, the cabling is often run through the air-handling space. Additionally, the access point itself may be installed in, or above, the suspended ceiling, requiring consideration of NEC requirements related to equipment installation in the ceiling.


The NFPA updates the NEC every two years. In prior years, there has been confusion related to the definition of “plenum” space, and what was permitted, and prohibited, in the “plenum” space.  The 2011 National Electric Code reconciles the terms “plenum” and “air-handling space” as follows.


-           NEC Article 300.22(C) “Other Spaces Used for Environmental Air (Plenums). This section shall apply to spaces not specifically fabricated for environmental air-handling purposes but used for air handling purposes as a plenum.


-          Article 300.22(C) Informational note 1 “The space over a hung ceiling used for environmental air-handling purposes is an example of the type of other space to which this section applies


In essence, the NEC is saying that (in most cases) “plenum” space and “air-handling” space is the same thing: the space above the suspended ceiling where cabling is run and wireless access points are often installed.





Furthermore, the NEC states in Article 300.22(C)(3)


Article 300.22(C)(3) “Electrical equipment with a metal enclosure, or electrical equipment with a nonmetallic enclosure listed for use within an air-handling space……. shall be permitted to be installed in such other space unless prohibited elsewhere in this Code


Article 300.23 “cables, race-ways and equipment installed behind panels, including suspended ceiling tiles, shall be arranged and secured so as to allow removal of panels and access to the equipment.”


AC line powered components should be in an approved enclosure in the plenum space. Access points that are listed or compliant to UL 2043 (Plenum rated components), and which are powered by Power over Ethernet (PoE), may be placed in the plenum space without an enclosure. UL listed, metal ceiling enclosures can provide the confidence that the installation is compliant with NEC 2011 requirements and will satisfy even the strictest local and regional code enforcement authorities, regardless of whether AC line power, or PoE, is used to power the electronics.


Also, when installing cabling and access points in, or above, a suspended ceiling, make sure there are not voids and holes left in the ceiling. Many ceiling systems have a burn rating which specifies how long the ceiling is expected to tolerate exposure to flame. Holes and gaps left in a suspended ceiling from access point installation can void a ceiling system’s burn rating.  Steel enclosures with solid (non-ventilated) back boxes can help to preserve the ceiling systems burn rating (consult ceiling manufacturer’s specifications for burn rating and installed components). Additional information on wireless network infrastructure is available at