Is there a legal way that complies with the USA-NFPA fire code, to put regular non-plenum network devices above a drop ceiling in a plenum airspace?
In many places in the United States, a licensed electrician is not required to install low-voltage cabling such as network and phone cables into residential or commercial buildings, nor is wiring inspection required. However, it is still important for unlicensed installers to follow electrical and fire safety rules outlined in the National Fire Protection code book.
For example it is not acceptable to install general purpose network electrical devices directly in a "plenum airspace", which is where the open air above a drop/suspended ceiling is used as an air return for the building ventilation. There is risk of a smoldering plastic fire in the hidden space, which is both fueled by the moving forced air fanning the flames, and the burning fumes are sucked into the building air circulation and can potentially unknowingly poison, injure, or kill building occupants.
Plenum rated network devices and plenum rated cables are specifically designed for plenum airspace use, with special expensive low smoke and self-extinguishing plastics.
EDIT: Further discussion for the inexperienced:
Wikipedia: Plenum space
(Yeah, um, I created this article back in 2012. The illustrations are my own work.)
Article: What Lurks in the Ceiling, Mar 24, 2011
Electrical Construction and Maintenance Magazine
- If a non-plenum device is partially or completely sealed off, such as putting the device in a covered metal enclosure with an electrical outlet inside, and the enclosure is itself installed by a licensed electrician for the device, is this sufficient to comply with the code? If a device failure and electrical fire were to break out, the metal enclosure would likely contain the fire, limit burning, and limit spread.
- Alternately, if that is not sufficient, would a gasketed metal enclosure with cable clamps or rubber bushings to limit air exchange through the punched cable openings be acceptable? This would further choke off the air circulation for any potential device overheating and fire so that it rapidly uses up its air supply in the enclosure, and go out.
- If an approved enclosure for a non-plenum device is available and workable, is it possible to cool the non-plenum device in some approved manner that limits air exchange and potential fire spread, such as a sealed air-to-air heat exchanger? (Also known as a fan blowing air in a circle inside, and a second fan blowing air on the enclosure shell on the outside.)