What Is A Plenum And Would You Run Cables Through One?

People in those parts of the world that turn to The Oxford Dictionary whenever they do not understand a word will argue that a plenum is:-

  1.     When a group or committee calls a full assembly of all its members (much the same as a plenary session).
  2.     To a physicist it would mean a space that is totally full of something (i.e. matter).

Both meanings have a Latin origin meaning “full space”.

However, supporters of Webster’s might put a slightly different slant on “plenum’s” second meaning above and think in terms of a space filled with air. They are not wrong; air is, after all, comprised of matter. This somewhat American definition is particularly applied to spaces within a building’s structure that can be used to receive air from a blower for heating, cooling and ventilation purposes within the building.

Typically, these plenum spaces are between a structural floor and the lowered ceiling beneath it. Alternatively the space below a raised floor could be utilized as a plenum space. NOTE – for either to be plenum spaces, the air must be able to be circulated. Also, the riser spaces in a building’s walls are not generally considered to be plenum spaces.

Safety In The Event Of A Building Fire

Architects and civil electrical engineers love to maximize space utilization and the thought of these empty (air filled) cavities all over the building led to the obvious conclusion that the plenum spaces would be great for hiding all the wires and cable systems required to power everything electrical within the building.

However, many electrical wires and cables are covered with insulation that is polymer based – plastics and/or rubber compounds. This was standard practice for years even though it was relatively common knowledge that, when ignited, many of these polymers would not only add to the spread of a fire; they would also give off toxic or poisonous fumes. These fumes would endanger the lives of firemen and survivors alike. (Don’t forget that there is airflow in these plenum spaces which will supply fresh oxygen and assist the combustion of any in there). The wiring placed within a plenum space is called Plenum Cable. For more visit http://www.customwireandcable.com/plenum-cable

In the United States, all Plenum Cable is subject to the rules of the National Fire Protection Association (NFPA) most of which are covered in their standard NFPA 90A. All the materials used in the construction of Plenum Cable have to pass the stringent fire safety test program set down in the NFPA 262 standard.

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