In building construction, a plenum is a separate space provided for air circulation for heating, ventilation, and air-conditioning. It is commonly found in the space between the structural ceiling and a drop-down ceiling or under a raised floor. In commercial settings such as schools or office buildings, the plenum space is often used to house connecting communication cables. Because ordinary cabling introduces a toxic hazard in the event of fire, special plenum cabling is required in plenum areas. Plenum-rated cable has special insulation that has low smoke and low flame characteristics.
Temperature-tolerant products, like plenum-rated cable, reduce the need for costly metallic conduit. The ability to utilize air-handling spaces for cable and equipment installation without conduit lowers costs. Yet, products installed in those air-handling spaces must conform to a higher safety standard. Experience gained from the grim aftermath of building fires led to standards directing the minimum quality and type of products that may reside within air-handling spaces. Only products specifically tested for compliance with NFPA 262 (formerly UL 910) and UL 2043 are legal for installation within air-handling spaces while requiring little or no additional fire barrier, such as conduit or other baffles.
Local building codes govern the type, approval, and placement of cables and devices mounted within the environmental air handling spaces of building structures. The local code authority, which is typically the city where construction occurs, adopts various fire safety codes generated by the National Fire Protection Association, or NFPA. The most well-known code is NFPA 70, the National Electrical Code (NEC).
Plenum and non-plenum cables can be any type of cable – Coaxial, Ethernet, HDMI, fiber optic, etc. The term “Plenum” and “Non-Plenum” simply refers to the outer jacket/cover that protects the cable.
Plenum-rated cables, also known as CMP (Communications Multipurpose Plenum), have the highest flame rating and the highest cost. They’re covered with a low-smoke polyvinyl chloride (PVC) or fluorinated ethylene polymer (FEP) fire-retardant jacket. The jacket is designed to restrict flame propagation within 5 ft, reduce the amount of smoke and toxic fumes released, and self-extinguish in the event of a fire. Thus, fire and building safety codes mandate plenum-rated cables be used in plenum spaces and air ducts. They can also be used in non-plenum areas.
Non-Plenum cables, on the other hand, are much cheaper and not as fire-resistant. When burned, they release toxic fumes such as hydrochloric acid and dioxin. Therefore, they may not be used in the plenum areas. Otherwise, deadly gases will rapidly circulate through the building. The two most common non-plenum cables are riser-rated cable or CMR (Communications Multipurpose Riser) and CM (Communications Multipurpose).
CMR cables are mainly used in risers and vertical shafts to run cable through multiple floors. They are designed to prevent fires from spreading between floors. CM cable is the least fire-resistant and the cheapest. It’s suited for general installations, like connecting a computer to a wall, and can also be used in areas without fire code restrictions on cable types.
“Communication Multipurpose Plenum”
“Communication Multipurpose Riser”
|Most fire resistant||Less fire resistant||Least fire resistant|
|Made for plenum airspaces, but can be installed anywhere||Mostly used for risers and vertical applications, but can also be used in non-riser spaces||For general use, or areas without fire code restrictions on cable types|
|Low-Smoke PVC or FEP Jacket||PVC Jacket||PVC Jacket|
|Releases a lower level of toxic fumes when burned||Releases a higher level of toxic fumes when burned||Releases a higher level of toxic fumes when burned|
|Most expensive||Less expensive than CMP||Cheapest|
In the United States, the National Fire Protection Association (NFPA) is in charge of setting fire and building safety standards regarding which cable jacket ratings can be installed in plenum or non-plenum areas and under what circumstances. Those standards are outlined in the NFPA’S National Electrical Code (NEC).
Before the cables can be sold and rated as CMP, CMR, or CM, they must undergo rigorous testing by one of the Nationally Recognized Testing Laboratories (NRTL) and meet or exceed the NFPA’s standards.
In partnership with top USA cable providers, NIA IT Solutions ensures that our cables meet NFPA safety standards for maximum safety.
Article 800 of the National Electrical Code (NEC) states that plenum cable should ALWAYS be used in plenum airspaces and air ducts to slow down the spread of flames and reduce smoke and toxic fumes from circulating throughout the building. Due to their higher safety standards, they can be freely installed inside plenum areas – no need to use a conduit. In addition, they can also be installed in non-plenum spaces.
Installing plenum cable in non-plenum spaces comes down to your budget, insurance, and building codes. For example, many commercial buildings, like schools, hospitals, and government facilities, are required to use plenum-rated cables in non-plenum areas to meet certain code requirements. Other businesses, on the other hand, choose to spend extra money on installing plenum cables in non-plenum areas to increase building safety and decrease insurance premiums.
While it’s definitely acceptable to use plenum-rated cable in your home to install a residential IP Camera, a WiFi network, or something else, more often than not, it’s not necessary. Most residential buildings don’t have plenum airspaces. Plenum areas are more common in commercial buildings. However, if your house does happen to have a plenum airspace or you need to run cables through an air duct, then plenum-rated cable is required.
Even though the NEC is not U.S law, it’s commonly enforced by state or local law. The NEC’S goal is to safeguard persons and property from electrical shocks, fires, toxic smoke, and other hazardous situations.
If building inspectors determine that CMP, CMR, or CM rated cables are not being used in the correct areas, your commercial building will not qualify for an occupancy permit, or you may be fined and expected to correct the issue (which can be expensive). Residential buildings must also adhere to NEC cable requirements. If property or life is lost due to a hazardous situation, you can be held liable for negligence due to code violations.
It’s best to comply with the code and spend a little bit of money upfront for the right cable rather than incurring a large expense when the consequences of violating the code hit you.
If you have additional questions about cable ratings, want to know which cable is the best for your system, or anything else, call us at 1-800-700-1262 or email us at (email@example.com) today.