Plenum Cable

Installation of cable must be compliant with local building regulations and fire codes. This means that specific cable types must be used in some installation scenarios.

A plenum space is a void in a building designed to carry heating, ventilation, and air conditioning (HVAC) systems. Plenum space is typically a false ceiling, though it could also be constructed as a raised floor. As it makes installation simpler, this space has also been used for communications wiring in some building designs. Plenum space is an effective conduit for fire, as there is plenty of airflow and no fire breaks. If the plenum space is used for heating, there may also be higher temperatures. Therefore, building regulations require the use of fire-retardant plenum cable in such spaces. Plenum cable must not emit large amounts of smoke when burned, be self-extinguishing, and meet other strict fire safety standards.

General purpose (non-plenum) cabling uses PVC jackets and insulation. Plenum-rated cable uses treated PVC or fluorinated ethylene polymer (FEP). This can make the cable less flexible, but the different materials used have no effect on bandwidth. Data cable rated for plenum use under the US National Electrical Code (NEC) is marked as CMP on the jacket. General-purpose cables are marked as CMG or MMG for PVC jackets, and CM or MP for plenum-rated cables.

Direct Burial

Outside plant (OSP) is cable run on the external walls of a building or between two buildings. This makes the cable vulnerable to different types of weathering:

• Aerial cable is typically strung between two poles or anchors. The ultraviolet (UV) rays in sunlight plus exposure to more extreme and changing temperatures and damp conditions will degrade regular PVC.
• Conduit can provide more protection for buried cable runs. Such cable can still be exposed to extreme temperatures and damp conditions, however, so regular PVC cable should not be used.
• Direct burial cable is laid and then covered in earth or cement/concrete.

OSP cable types use special coatings to protect against UV and abrasion and are often gel filled to protect against temperature extremes and damp conditions. Direct burial cable may also need to be armored to protect against chewing by rodents.