Plenum vs Riser Cable: Which One to Choose

FACTS CHECKED BY  Jose George​

The NEC (National Electrical Code) gives different ratings to cables based on their usage. And businesses must consider these ratings when installing new lines or hiring a cabling contractor. Examples of these ratings are:

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  • CMP cables for communications plenum.
  • CMR cables for communications riser. 

These ratings only indicate the cable jacket’s fire-resisting properties, and it has no relation to a cable’s data transmission capacity. Most commercial buildings use either a riser or plenum-rated cable to meet fire safety standards, but what’s the difference? Let’s dig into plenum vs. riser cable.

Plenum (CMP) Vs. Riser (CMR): Cable Types for Cat 5 and Cat 6 

Some cables like HDMI, DVI, twisted pair, and coaxial cables are available in riser and plenum versions.

Plenum Cable (CMP):

A space provides easy airflow to the heated/conditioned air from the heating and AC systems. This space is referred to as the plenum. For example, the distance between the raised and structural ceiling or under a raised floor. Electricians install communication cables for telephone and computer networks in this plenum space. 

However, plenum spaces may risk significant fire accidents as the fire gets oxygen to burn more in plenum spaces. The ASHRAE or the American Society of Heating, Refrigerating, and Air-Conditioning Engineers says that accumulated cable bundles can limit the flame, but they can damage other structural components. You should not use a plenum space for storing abandoned cable or a piece of high-voltage equipment as it can catch fire.

The NFPA90, a standard of the National Fire Protection Association in the US, regulates the plastics used in plenum cables. The plenum cable jacket comprises low-smoke PVC (polyvinyl chloride) or FEP (fluorinated ethylene polymer). The NFPA 90A mentions the fire safety standards by NFPA 262, and all cables and wires used in plenum spaces must meet these safety code standards.

Note: 

Sometimes ductwork disconnection occurs due to earthquakes, adverse environmental conditions, and aging. As a result, some non-plenum space converts into the plenum. Finding such unwanted plenum space can be challenging due to its minor hidden nature. Thus, to correctly identify a plenum space, you should only consider drop ceilings as plenums. 

In addition, there are concerns about using fluorinated chemicals in the plenum cables as they are human carcinogens. Thus, the NFPA Technical Committee on Air Conditioning has started developing non-halogen plenum cable compounds.

Image: electrical cables and pipes on the house concrete ceiling

Riser Cable (CMR)

A riser refers to the vertical shaft where you can vertically distribute electrical conduits, water supply lines, and communication cables. A riser can be a separate room on every floor for communication cables. In such a situation, the room is self-contained, and there is no circulating air for the HVAC system. A cable that runs in these riser areas is a riser cable. There are no strict fire regulations for a riser cable, and it means that you can replace a riser cable with a plenum cable but not vice-versa. 

Cat5e Riser Cable VS Cat5e Plenum Cable: Fire rating

Cat 5 cable/category five cables are twisted pair cables that you use for computer networks. These network cables provide performance up to 100 MHz bandwidth with a speed of 1GB speed at a distance up to 328ft. Since 2001, the cat 5e variant has been most commonly used in this category. The TIA standard 568.2-D rating applies to these cat5e cables.

For both cat 5e plenums and risers, some solid conductors or wires provide strength and excellent performance for long distances. They differ in:

Fire rating

A cat 5e riser cable has polyolefin insulation that covers its copper wire. Further, these cables’ jacket material comprises Flame-Retardant Polyvinyl Chloride (FRPVC). This material prevents the flame from spreading. On the other hand, cat 5e plenum cables have the highest fire-resistive rating on ethernet cables. It has FEP (Fluorinated Ethylene Propylene) insulation and jacket material composed of Low Smoke Flame Retardant Polyvinyl Chloride (LSFRPVC), which is different from that of the riser. These compounds prevent the spread of smoke down the jacket.

Application

You can use a cat 5e riser cable at home, businesses, risers, beneath the floor, attics, and in the wall. You cannot use this cable type in plenum spaces but vice versa. On the contrary, you can use a plenum cat 5e cable in plenum spaces, air ducts, and drop ceilings.

Cost

While plenum cat 5e cables are costly, cat5e riser cable offers an affordable and cost-effective solution.

Image: Modern conduits with wires in the room

Cat 6 Riser Cable VS Cat 6 Plenum Cable

As the communication industry adopted gigabit ethernet (1000BASE-T), there was a need for a new cable that could meet industry standards. The new line must transmit at a higher frequency of 250MHz, where Cat 6 came into existence. Cat6 meets strict specifications for cross-talk, and it has a thick wire gauge and better shielding. Also, the wire has more twists per inch which reduces signal loss. The cat six cables can reach up to a 10-gigabit ethernet speed when cable length reduces to less than 50m.

Also, cat six plenums and risers share the same conductors. They differ in:

Fire rating

Cat 6 plenum cable jacket comprises low-smoke polyvinyl chloride (PVC) or a fluorinated ethylene polymer (FEP). These compounds offer higher chemical resistance and better electrical properties. It prevents floor to floor spread of flames. It helps restrict flame propagation by supporting a temperature ranging from -25to 125 degrees Celsius. In contrast, Cat 6 Riser cable has a jacket of inexpensive Polyvinyl chloride and can operate at a temp. Range of 0-70 degrees Celsius. 

Application

Cat 6 plenum cables are fit to use in plenum spaces. On the other hand, you can use Cat 6 riser in vertical installations. 

The Cat 6 plenum cables meet the strictest UL910 standards. On the contrary, Cat 6 riser cables meet UL1666 standards, which is not as challenging as the former. As a result, these cables are in high demand. As the riser cable requirements are low and you cannot replace a plenum cable with a riser cable, keeping only plenum cables for storage and inventory is good.

Cost

Because of these high-quality fire-retardant compounds, plenum cables are costlier than riser cables.

Conclusion

Plenum cables ensure the safety of the building and its residents. Plenum cables have to meet strict fire safety standards, and the materials to meet these standards are costly. As a result, the cost of plenum cables is higher than non-plenum cables. Further, you cannot use a riser-rated line at plenum spaces. 

If you are looking for plenum cables,  feel free to call us. We deal in several coaxial and twisted pair cables, ensuring that our lines meet all safety standards. 

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