What Is a Riser Cable?

Once a cable has been installed, it can easily be “out of sight, out of mind”, especially if it was installed behind walls, under floors, or above ceilings. However, the location of a cable within a building can trigger a code-mandated requirement to install a properly fire-rated cable within that space. Read on for information on riser cables, the correct areas to install a fire-rated riser or plenum cable, and more.

What is a riser cable?  

A riser cable’s name can also be shortened to CMR, standing for “Communications Riser”. To understand what a riser cable is, it is helpful to understand what a riser is. The vertical shaft, region, or multitude of rooms between two floors within a building is a riser, and the cables used in these areas are distributed vertically.

Per an article by Belden, “Both riser and plenum cables have fire ratings they must meet and are utilized to prevent the spread of fires. However, the fire rating for plenum cables is stricter than that of riser cables.”

UL Solutions not only notes the importance of plenum and riser cable materials, but also the “selection and installation practices” that need to be followed to mitigate any damage or harm in these potentially serious fire risk areas.

Riser cables have to be made so that flames do not move from one floor to another. Riser rated cables must be assessed to adhere to UL 1666, the Standard for Test for Flame Propagation Height of Electrical and Optical-Fiber Cables Installed Vertically in Shafts.

UL Solutions specifies these requirements, “For cables used in risers, the pass/fail criteria for UL 1666 are that the flame propagation height of each set of cable shall not equal or exceed 12 feet, 0 inches (3 m, 66 cm) and that the temperature of any thermocouple in the second floor slot shall not exceed 850 degrees F (454.4 degrees C).”

Plenum cable

A plenum cable must be used in a plenum area, which is a building’s air-handling space. Communications plenum (CMP) cable has more stringent requirements to be met because plenum areas can quickly move flames and smoke within a building. Due to this potentially serious fire risk, telecommunications cables designed to be used in plenum spaces need to meet meticulous requirements for limited smoke production and fire resistance. The National Fire Protection Association (NFPA) has the “Standard Method of Test for Flame Travel and Smoke of Wires and Cables for Use in Air-Handling Spaces”, test standard NFPA 262, to prevent and inform on these hazards.

UL Solutions describes NFPA 262’s standard, “For cables used in plenums, the pass/fail requirements for NFPA 262 are a maximum peak optical density (POD) of 0.50 or less, an average optical density (AOD) of 0.15 or less and a maximum flame spread distance of five feet or less.”

The importance of national safety requirements

If either plenum or riser cables do not meet the national safety requirements shown in ANSI/UL 444, the cable’s reaction in the case of a fire may lead to loss of life and/or damage to property. This safety threat particularly applies to cables manufactured utilizing deficient manufacturing processes and below-standard materials. UL Solutions confirms that, “Without third-party certification, which includes such activities as evaluation of the materials and construction, as well as testing and surveillance, non-compliant cables running through a structure can accelerate the spread of smoke and flame.”

Ensuring a riser or plenum cable is suitable for a building comes from being able to identify a properly labeled and certified cable. Not only should one be able to comprehend the information surface-printed on the cable, but they also must know what needs to be included on a label, carton, reel box, or smallest unit container. When it comes to the UL Mark the company states, “The UL Solutions symbol on the product and the Certification Mark of UL Solutions, on the attached tag, reel or the smallest unit container in which the product is packaged, is the only method provided by UL Solutions to identify products manufactured under its Certification and Follow-Up Services.”

When the UL Mark is on a product, the manufacturer is confirming that the product has met UL Solutions requirements when it was produced. UL Solutions says to be suspicious of a product where one or both are missing. In an effort to further help with identifying if a product is counterfeit, all products in telecommunication cable categories certified by UL Solutions must bear a unique UL Solutions holographic label.

To find more information on counterfeit cables and UL Solutions’ market survey data showing the compliance of self-declared (unlisted) cables, click here.

Which cable should be used?

The main factor to be considered when deciding on a cable for installation in a building is the area where the cable needs to be installed. Communications general purpose (CM) cable can only be installed in a space that is not a riser or a plenum. To ensure compliance with the law, one must install the correct fire-rated cable into a building space (i.e., CMP in plenum space, CMR or CMP cable in riser space, and CM in neither riser nor plenum spaces). The building code is the law that must be adhered to, and a violation of plenum or riser requirements is a violation of that law.

Although it may be more budget-friendly to use riser cables, it should not come at the expense of safety. As mentioned previously, both riser and plenum cables can be used in installations in non-plenum areas. However, riser cables should not be used in place of plenum rated cables in plenum areas. This is simply because if there is a fire, with plenum cables the damage is reduced, and their slower burn time gives anyone in the building more time to get to safety. Using the right cable in the correct area is not only a good practice and abiding by the law, it also reduces possible losses in the future in the case of a fire.