Plenum cable ([email protected]) is an electrical cable that is installed in building plenum areas. Plenum cable is jacketed with a fire-retardant plastic jacket made of either low-smoke PVC or fluorinated ethylene polymer (FEP). The metal conductors are stranded for ease of handling and to increase the cable's bending strength.
The word "plenum" comes from the term "public lighting environment". It refers to large areas inside buildings where smoke from burning material can spread.
Smoke alarms and fire extinguishers should be placed in all public areas, including office spaces, storage rooms, and hallways.
Electrical power cables that run through these areas must be able to carry current without damage due to heat. This requires special insulation materials that will not break down when exposed to high temperatures. Typical residential power cables can be used for this purpose but they do not provide enough resistance to cooling air currents found in larger buildings. Cables designed for use in plenum areas can be made from polyethylene or other high-heat-resistant plastics instead of normal wire.
Cable manufacturers label certain types of cable as "plenum" because they're suitable for use in public areas. These cables are usually thicker and have more protective layers than regular household wiring. They also tend to be black or white with red or green wires rather than orange or gray.
Plenum-rated cable is named after an HVAC term: plenum spaces. Plenum spaces are those that exist between a drop and a regular ceiling (or a comparable version on the floor space), and it is via this segment that air flows in a structure, assisting in heating and cooling functions. HVAC professionals call these passages pipe runs.
Pipe runs can be quite large, often 16 or 24 inches in diameter, and they are necessary to allow for proper ventilation within a building while also providing a way for heat to escape in the winter and air to move in during the summer. For this reason, cable manufacturers specify which sizes of pipe run will accept their cable products. Cable suitable for use in plenums must be labeled as such. The phrase "for plenum application" should appear on the label or packaging.
Cable designated for use in plenums is usually black or dark blue in color. It is covered with protective material called shielding, which prevents electricity from leaking out through the cable and reduces interference from other electrical devices. When installing cable in a structure, care should be taken not to cut any of the shielding off of the cores.
There are two types of plenum cables: continuous core and discrete core.
With continuous core cable, each individual conductor within the cable is protected by wrapping it in foil or another type of shielding.
Plenum-rated cable has a particular insulation that is low in smoke and flame. Plenum cable must be placed in all "air handling" spaces. This makes this ceiling a plenum ceiling, and any wires that go through it must be plenum rated.
The main advantage of using plenum-rated cable is that you can run other types of wiring next to it without worrying about electrical interference from vibrations or other movement caused by the live power cables. The only requirement for non-plenum cable is that it must be covered with an electrical tape to prevent contact with live power.
Besides being plenum rated, what else does cable have to do to be considered "non-metallic"? Non-metallic cable (NMC) is used in interior permanent lighting fixtures and some other applications where it is important that electricity not conduct into the lamp holder or terminal block. NMC also cannot be magnetized like metal, so it can't be used as wire for a magnetic switch such as a doorbell magnet.
NMC is made up of four components: internal conductor, protective covering/bulkhead, filler material (usually plastic), and insulation. Internal conductors are defined by solid sheets of metal sandwiched between two layers of protective materials. These metals can be aluminum, steel, or copper. Each type of metal has its advantages and disadvantages when used in NMC.
Exposure to these gases might therefore impede the proper evacuation of persons in the area, leading to an increase in mortality. Plenum-rated cable has an unique coating on the wire that allows it to burn at a greater temperature and generate less fumes than standard PVC. This rating indicates that the cable can with stand being in contact with fire for longer periods of time without damaging the insulation or core of the wire.
The term "plenum" comes from the word "plenum chamber," which is the name given to a portion of an electrical distribution system where high-voltage power is distributed through conduits of varnished fiberboard or steel. These areas are accessible only through special plenums, or ducts, which run along the ceiling and wall surfaces of buildings. The term "plenum cable" refers to any type of cable suitable for use in a plenum environment.
In addition to being resistant to flame, plenum-rated cable can also with stand temperatures up to 120 degrees Celsius (248 degrees Fahrenheit). This makes it suitable for use in hot water heaters and other appliances where there is risk of overheating.
Plenum-rated cable is required by law in some states where it's installed. It must be used in place of standard cable if the room it's being placed in contacts with flame or intense heat regularly.