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HomeTips & GuidesDefine Plenum Cable: Everything You Need To Know

Define Plenum Cable: Everything You Need To Know

Whether you’re a DIY homeowner or a professional cable installer, it’s important to know when to use non-plenum or plenum-rated cables. The right cable will ensure your residential or commercial is safe and up to code. The article below will define plenum cable and where you can use them.

How to Define Plenum Cable?

When we refer to plenum cables, we are not referring to a type of cable (HDMI, ethernet, coaxial, etc) but the fire retardance of a cable jacket.

In the US, the NFPA outlines the electrical wiring standards for buildings in the NEC (National Electric Code).

Since the NFPA’s main purpose is preventing fires, most local bodies and state governments adhere to NEC guidelines as part of the building code.

Coaxial Cable

Coaxial Cable

There are more than 15 cable rating levels according to NEC guidelines. However, the 3 most popular cable ratings include;

Plenum Rated Cable (CMP)

  • Most expensive
  • Made from low-smoke FEP or PVC components
  • High fire retardness rating
  • Suitable for air ducts and plenum spaces

Riser Rated Cable (CMR)

  • Often referred to as PVC cable since the jacket is commonly made of inexpensive PVC components.
  • You can use it in risers.
  • Lower fire retardness rating compared to plenum-rated cable, but higher than standard cables

General Purpose (CM) Cable

  • You can use it near floors and on walls
  • Often used for jumpers and patch cords
  • Useful when fire codes don’t have any restrictions regarding cable types

When Should One Use a Plenum Cable?

The majority of building codes dictate that CMP (plenum-rated) cables can only be used in air ducts and plenum spaces.

For massive public spaces such as airports, hospitals, and schools, building codes in a number of towns and cities allow you to use plenum-rated cables for non-plenum-rated spaces.

The most popular plenum-rated spaces are often below floors and above drop ceilings. In most commercial buildings that have an HVAC system, the air duct supplies air from the outside HVAC system into the building’s interior. However, the return air moves through an open space on top of the drop ceiling instead of turning it into a plenum space.

These spaces are vital for air circulation. However, due to the high airflow rate, they are a fire hazard. If you use a non-plenum-rated plastic cable in such a space, the fire will spread faster and release harmful toxins throughout the entire building. 

The primary agenda is to prevent fires from moving through cables and spreading throughout the entire building.

Why Use a Plenum Cable?

CMP (plenum-rated) cables feature an outer cable jacket made of a fire-retardant material, such as Teflon, to prevent fires from spreading.

In case of a fire, plenum-rated cables are designed to;

  • Self extinguish
  • Limit the level of harmful toxins released
  • Restrict flame propagation to under 5 feet 

If you use a non-plenum-rated cable in a plenum space, inspectors will not grant you a building permit or occupancy, and you might have to pay fines.

Although many residential buildings don’t undergo inspection, it’s still essential that you follow local codes. If there’s a fire and you did not use the correct cable, you could be held accountable for negligence, and you might not be able to claim your insurance.

When Could You Use a Non-Plenum (CMR, CM) Cable?

You can use non-plenum cables everywhere except in air ducts and plenum spaces. In both residential and commercial buildings, you can use non-plenum cables to run cables across open ceilings and through walls. However, when running cables through vertical shafts or risers, you must use riser-rated (CMR) cables.

Some buildings have HVAC systems with return air ducts that move air back outdoors. If the space on top of a drop ceiling isn’t circulating any air and there are no leakages, you can use non-plenum-rated cables. However, keep in mind that this is only if the cable isn’t running inside the air ducts.

RSRF RS600, RSRF RS400, Times Microwave LMR600, and Times Microwave LMR400 are common non-plenum-rated coax cables, all of which can be obtained at Cloom.

Using CM or CMR cables is significantly cost-saving as they normally cost a third or half the price of CMP (plenum-rated) cables.

However, before you make a decision, confirm with your insurance and local area building code. Some building codes and insurances require plenum-rated cables, even in non-plenum-rated spaces, depending on factors such as building occupancy, height, and purpose.

Do You Require a Plenum Rated Cable If it is in a Conduit?

If you are using a conduit that is plenum-rated, then you don’t have to use a plenum-rated cable. This is valid even if your conduit is in a plenum space. The popular types of plenum conduit are metal and inner ducts (commonly used in fiber runs). 

However, buying plenum-rated cables is easier and cheaper to install compared to installing plenum-rated conduit.

How Do You Know If a Cable is Plenum Rated?

In the United States, the UL (Underwriter’s Laboratory) certifies cables. If your plenum-rated cable has a UL trademark and several approvals, you can check the UL website to verify that it’s legitimate.

However, some cables meet the plenum rating standards but don’t have UL certification. Depending on your jurisdiction, you might need to illustrate that your cable is plenum-rated. However, in some jurisdictions, you might need to prove UL certification in addition to illustrating that your cable is plenum-rated. 

Below is a list of coax cables that are UL-certified plenum-rated.

  • Commscope Heliax AL4RPV
  • Ventev TWS-400-P
  • Wilson 400 Plenum Cable
  • Times Microwave LMR-600-LLPL
  • Times Microwave LMR-400-LLPL

Also, here’s a list of cables that meet the plenum rating but aren’t UL-certified.

  • RSRF RS400-PL Plenum Cable

Normally, UL-certified cables should have a UL trademark label and approval number, which you can find on the UL official website.


There you have it—all you need to know about plenum cables, from where to best use them to the other types of cables for different scenarios. Knowing this, you can make a more informed decision when installing your cables. For all your plenum cable needs, feel free to contact Cloom Tech.

I am Lillian Yang, having been a sales manager for over 10 years.

I have received many positive reviews from customers. They have praised our excellent service, on-time delivery, and high-quality cable assemblies.

For your projects, please provide cable assembly files/images/smples, etc., so that I can send you a quotation within 24 hours.

Contact me now and let’s get started on building your wire harnesses!

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