When it comes to communication cabling in buildings, safety is more than just performance — it’s about preventing fire spread and protecting lives. CMP Cable, the highest fire-rated category, plays a critical role in ensuring compliance and safety in plenum spaces such as HVAC ducts and ceiling voids. Understanding the difference between CM, CMR, and CMP helps professionals make the right choice for both safety and cost-efficiency.

What is CMP Cable? Definition and Standards?

CMP (Communications Plenum) refers to the highest flame-resistance rating for communication cables, defined by the National Electrical Code (NEC, Article 800). CMP cables are designed for plenum spaces—areas that circulate air, such as air-handling ducts or spaces above drop ceilings.

To achieve CMP certification, cables must pass the NFPA 262 / UL 910 Steiner Tunnel test, which measures flame spread and smoke generation. This ensures that CMP cables produce very little smoke and resist flame propagation, significantly reducing toxic hazards in fire scenarios.

What Are CM, CMR, and CMP Fire Ratings?

In North America, building codes require different fire-resistance levels for communication cables based on their installation environments. These levels — CM（Communications Cable）、CMR（Riser Cable）、CMP（Plenum Cable）。 — are defined by the National Electrical Code (NEC) and certified by Underwriters Laboratories (UL). Each type is subject to specific flame tests and is intended for use in different building zones with varying fire safety requirements.

Comparison of CMP and Other Cable Ratings

Type	Fire Rating	Application	Cost
CM	Basic	Residential or general-purpose wiring	Low
CMR	Riser-rated	Vertical shafts in multi-story buildings	Medium
CMP	Plenum-rated	Air ducts, ventilation spaces, above ceilings	High

 

Fire rating hierarchy from lowest to highest: CM < CMR < CMP

 

CMP（Plenum Cable）｜The Highest Fire Rating

Application

CMP cables are designed for plenum spaces—areas with high air circulation such as air handling ducts, spaces above drop ceilings, and below raised floors. Due to the increased risk of fire spread in these areas, CMP cables offer the most stringent fire protection.

Standard Compliance

CMP cables must meet NFPA 262 standards, which assess flame spread and smoke generation in horizontal flame tests. The flame spread must not exceed 1.5 meters, with maximum smoke density under 0.5 and an average below 0.15. Typically built with fluoropolymer insulation, CMP cables limit toxic smoke and reduce the risk of secondary fires, enhancing occupant safety during evacuation.

 

CMR（Riser Cable）｜Vertical Flame-Retardant for Between Floors

Application

CMR cables are intended for vertical runs, such as inside riser shafts, stairwells, or elevator conduits. These areas act as fire pathways, so CMR cables are designed to prevent flames from spreading rapidly between floors.

Standard Compliance

CMR cables must pass the UL 1666 flame test, which simulates vertical cable burn scenarios. Their outer jackets are typically made from flame-retardant PVC, providing an extra layer of protection to prevent fire from traveling along the cable and affecting multiple floors.

 

CM（Communications Cable）｜Basic Flame Rating for General Use

Application

CM cables are suitable for general in-room wiring such as network, telephone, and audio/video connections inside walls or server rooms. While they don’t offer the same fire resistance as CMR or CMP, they are adequate for low-risk areas.

Standard Compliance

CM cables must comply with UL 1685 and pass vertical tray flame tests. These cables are generally used in homes or standard office environments where fire risks are lower and premium-rated cables are not required.

 

CM, CMR, and CMP cables are used in different spaces based on required fire protection levels.

Why Use CMP Cable and How to Choose

• When CMP is required: If cables are installed in plenum spaces, NEC requires CMP due to the high fire risk.
• When CMR is sufficient: For most vertical shaft applications, CMR is adequate and cost-effective.
• How to decide: Evaluate the building’s airflow design and consult local building codes to ensure compliance while avoiding unnecessary overspending.

 

Common Application Scenarios

CMP cables are typically deployed in:

• Data centers and server rooms requiring extensive cabling.
• HVAC air ducts or ceiling spaces in high-rise or commercial buildings.
• Large-scale surveillance systems that must meet strict safety codes.

 

European Fire Safety Standards for Cables

 

Fire safety regulations for cables in Europe differ from those in North America and are governed by the Construction Product Regulation (CPR). Under CPR, electrical and communication cables are considered construction products and must meet strict fire performance requirements before being placed on the market.

Cable fire resistance is classified according to EN 50575:2014+A1:2016, which evaluates factors such as heat release rate, flame spread, and smoke production. The fire classes include:

• B2ca: Highest fire performance, suitable for high-risk environments like tunnels, airports, and hospitals.
• Cca、Dca: : Medium performance, commonly used in commercial buildings and shopping centers.
• Eca: Basic fire protection, for low-risk settings such as residences and factories.
• Fca: Non-fire-resistant, for outdoor use.

 

Testing methods used to determine fire classification include:

• EN ISO 1716: Measures total heat of combustion.
• EN 60332-1-2: Assesses flame propagation in a single cable.
• EN 50399: Evaluates heat release and smoke production in bundled cables.
• EN 61034-2: Measures smoke density during combustion.
• EN 60754-2: Determines acidity and corrosiveness of combustion gases.

 

Additionally, IEC 60332 standards are used internationally:

• IEC 60332-1-2: Tests flame propagation in a single insulated cable.
• IEC 60332-3-A~D: Tests flame spread in bundled cables, with Class A to D representing increasing levels of stringency based on the installation's fire risk.

 

Cable Fire-Resistance Ratings

Euroclass (ca)	Classification Criteria	Smoke production EN 50399 / EN 61034-2	Flaming droplets EN 50399	Acidity EN 50267-2-3	Risk of Fire	Installation Place / Environment example
B2	EN 50399 Heat release Flame spread	s1a / s1b	d0	a1	Very High	hospital, tunnels, underground railways, high rise building with large of occupants
C	EN 50399 Heat release Flame spread	s1	d1	a2	High	airports, shopping centers, public buildings, escape routes
D	EN 60332-1-2 Flame propagation	s2 / s3	d2	a3	Medium	commercial premises, large office, large storehouses
E	EN 60332-1-2 Flame propagation	–	–	–	Low	single residential, industrial premises, small store building with few occupants
F	Fails to meet E ca, Not advisable for public places	–	–	–	–	Outdoor installation and use only

 

 

In summary, European fire safety standards for cables cover a comprehensive range of tests—from single cable flame propagation to bundled cable fire performance. Based on these test results, cables are classified into distinct fire-resistance categories. These regulations ensure that, in the event of a fire, the cables used within buildings significantly reduce flame spread and smoke generation, ultimately enhancing occupant safety.

Technical Details

CMP cables must comply with stringent testing

• NEC Article 800 governs communication cable standards.
• NFPA 262 / UL 910 Steiner Tunnel test ensures low flame spread and smoke emission in horizontal installations.

By combining these requirements, CMP cables offer superior fire safety for critical infrastructure, balancing durability, compliance, and performance.

How to Choose the Right Fire-Rated Cable?

 

Choosing the right fire-rated cable is essential to minimizing fire-related losses. Depending on the installation environment—whether in general office spaces, air handling systems, or vertical shafts—cables must comply with relevant standards such as NFPA 262 or UL 1666.

With the rise of smart buildings and the Internet of Things (IoT), safety considerations are evolving. PoE (Power over Ethernet) and PoH (Power over HDBaseT) systems increase the demand for cables that not only resist fire but can also safely handle power transmission without overheating.

Fire safety is no longer the only concern—today’s cables must also meet the electrical safety demands of tomorrow’s intelligent infrastructure.

 

The Future of Fire-Rated Cabling in the IoT Era

 

As IoT continues to expand, PoE technology—which delivers power and data through a single Ethernet cable—has become a standard solution in modern infrastructure. However, it also introduces heat buildup inside the cable. Emerging PoH (Power over HDBaseT) technologies place even greater thermal demands on cabling systems.

Currently, UL Solutions is the only global body providing safety certification specifically for cable power transmission. As an industry leader, Wonderful Hi-Tech works closely with UL to ensure our flame-retardant cable products meet the latest performance and safety requirements.

 

PoE devices deliver both power and data through a single twisted-pair cable.

 

At Wonderful Hi-Tech, we are committed to delivering top-quality cable solutions with leading-edge safety and fire protection technologies.

To learn more about our fire-rated cable offerings, contact us at: sales@wontex.com.tw

Let us safeguard your cable infrastructure — today and into the future.

FAQ

1. What is the difference between CMP and CMR?
CMP is plenum-rated for air-handling spaces with higher fire safety, while CMR is riser-rated for vertical shafts.

2. Do residential buildings need CMP cables?
Most homes don’t require CMP unless plenum spaces are part of the HVAC system.

3. Why is CMP more expensive?
It uses flame-resistant fluoropolymer materials and undergoes stricter testing.

4. What happens if CMR is used instead of CMP in plenum areas?
It violates code compliance, increases fire hazards, and can fail inspections.

5. How long does CMP last compared to other cables?
It has a similar lifespan to other Ethernet cables but offers greater durability in high-temperature environments.