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.

 

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.

 

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.

 

International Cable Fire Resistance Standards: Fire test results provide a critical reference for selecting safe cabling in buildings.

Category	Certification	Fire (Btu/hr)	Length (ft)	Test Time	Test Method		Application	Insulation	Jacket
LSOH	IEC60332-1		1KW 3414btu, 60CM, 50MM↓	Based on OD, burn for 60~480 sec	Vertical	Equivalent to CM rating	Single Cable	HDPE	LSOH
	IEC60332-3-22 A	7 l/m	70,000btu, 3.5M, 2.5M↓	40 min	Vertical	Equivalent to CMR rating	Bundled Cables	HDPE	LSOH
	IEC60332-3-23 B	3.5 l/m		40 min
	IEC60332-3-24 C	1.5 l/m		20 min
	IEC60332-3-25 D	0.5 l/m		20 min

 

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.

 

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.