CM/CMR/CMP/CMX: Ethernet cable fire rating and applications

In industrial environments, where heavy machinery, high electrical loads, and flammable materials are frequently present, fire safety is always a top priority. Industrial ethernet cables, which serve as the backbone of modern automation networks, must operate reliably under harsh conditions such as high temperatures, intense vibration, mechanical impact, and potential explosion hazards.

There are three key reasons why fire-resistant performance is a mandatory requirement in industrial network systems:

1. High-risk operating environments: Factories, industrial zones, oil and gas facilities, and food processing plants all contain heat sources, chemicals, and complex wiring systems that can easily lead to fire or explosion incidents.
2. Minimizing fire propagation risks: Flames can quickly spread along cable trays or bundles, potentially paralyzing entire production lines, damaging critical equipment, and endangering human lives.
3. Compliance with standards and regulations: Modern building, fire safety, and insurance regulations require the use of certified fire-resistant cables - or even higher-rated types in industrial systems.

Most industrial ethernet cables are designed with fire-resistant properties. However, the level of fire resistance varies depending on the materials used, cable construction, and the specific certification standards they meet.

Overview of industrial Ethernet cables and HELUKABEL Ethernet cable types

To assess the fire-resistant performance of industrial ethernet cables, international organizations have developed a variety of test methods that determine a cable’s fire endurance and ability to limit flame propagation under real-world conditions. Below are the most widely recognized and applied standards in the industry:

2.1 UL VW-1 (UL 1581) – Vertical Wire Flame Test

This is one of the most common flame tests, developed by Underwriters Laboratories (UL).
The VW-1 test simulates a scenario where a cable burns in a vertical position to evaluate its ability to self-extinguish and limit vertical flame spread. A cable meeting UL 1581 VW-1 demonstrates strong flame-retardant capability, making it suitable for automation systems, industrial facilities, and data centers, where high levels of fire safety are required.

2.3 UL 1685 – Vertical Tray Flame Test

The UL 1685 standard evaluates how flames spread when multiple cables are installed vertically in a cable tray - a common setup in factories and industrial plants. This test replicates real-world conditions where hundreds of ethernet cables may run side by side in the same cable path. Cables that pass UL 1685 demonstrate excellent ability to prevent flame propagation across bundled installations, ensuring enhanced overall fire safety in industrial network infrastructures

2.4 CPR standard (Europe)

Within the European Union (EU), the Construction Products Regulation (CPR) classifies cables based on their reaction to fire, from Aca (non-combustible) to Fca (highly flammable).
Among these, ratings such as B1ca, B2ca, and Cca represent increasingly higher safety levels suitable for use in buildings and structured cabling systems.

Learn about the CPR fire classification system in Europe

2.5 NFPA 70 / NEC – National Electrical Code

The NFPA 70, also known as the National Electrical Code (NEC), is the U.S. national standard for electrical safety, covering fire prevention, electrical protection, and cable installation practices. It defines specific fire-resistance classifications for communication and Ethernet cables, helping users select the correct type for each installation environment.

Compliance with NFPA 70 / NEC ensures that industrial ethernet systems meet fire safety, insurance, and legal requirements in the United States and internationally.

Ethernet cable jacket ratings define the safety level and performance characteristics of network cables, as specified by the National Electrical Code (NEC). These classifications ensure that ethernet cables are installed and used safely across various environments.

Abbreviations such as CM, CMR, CMP, and CMX indicate different types of cable jackets - each offering distinct levels of flame resistance and safety, suitable for specific applications.

3.1 CM-rated ethernet cables

CM (Communications Multipurpose) cables are designed for general-purpose use, ideal for standard areas that are not part of air-handling spaces (non-plenum areas).

The jacket of a CM ethernet cable is typically made of PVC and must pass a standard vertical flame test to receive CM certification. These cables are tested in accordance with UL 1581 and CSA FT1 standards, which represent the basic level of flame resistance required for communication cables.

While CM-rated cables offer limited fire protection, they still meet the minimum safety requirements for indoor applications. Their main advantages include affordability, flexibility, and ease of installation, making them a popular choice for short-distance networking in homes and office environments.

Most Cat6 and Cat6A cables available on the market today meet CM rating standards, meaning they are safe and compliant for typical residential and office network systems.

Some of HELUKABEL's CM cable products include HELUKAT® 500IND CAT.6A S/FTP FRNC STATIC (11007777), HELUKAT® 500S CAT.6A SF/FTP PVC CHAIN (805704), HELUKAT® PROFInet A CAT.5e SF/UTP FRNC STATIC(805653), HELUKAT® PROFInet B CAT.5e SF/UTP FRNC FLEX(805654), HELUKAT® PROFInet B CAT.5e SF/UTP FRNC SHIPLINE(802185).

Learn about the characteristics of Cat5, Cat6, and Cat7 network cables

3.2 CMR-rated ethernet cables – Riser cables

CMR (Communications Riser) cables are specifically designed for vertical installations, where cables run between floors in multi-story buildings. They are subject to stricter fire safety requirements than CM cables and are tested according to UL 1666 and CSA FT4 standards.

Constructed from flame-retardant materials such as low-smoke PVC or, CMR cables are engineered to prevent flames from spreading between floors, providing a safer solution for vertical riser shafts and building cores.

Due to their enhanced fire resistance and durable construction, CMR-rated ethernet cables are ideal for riser applications in multi-story commercial or residential buildings. They can also serve as a safer alternative to CM cables when higher fire safety performance is required. However, CMR cables are not suitable for plenum spaces - areas with air circulation for heating or cooling systems, where stricter fire and smoke requirements apply.

3.3 CMP-rated ethernet cables – Plenum cables

CMP (Communications Multipurpose Plenum) cables represent the highest level of fire safety among ethernet cable types, as defined by UL and CSA standards. The term “plenum” refers to air-handling spaces within buildings such as drop ceilings, raised floors, or HVAC air ducts - where air circulation for heating and cooling occurs. These spaces require cables that emit minimal smoke and toxic gases in the event of a fire. CMP cables are tested according to UL 910 or CSA FT6, which assess both flame spread and smoke generation under rigorous conditions.

Manufactured primarily from FEP or other low-smoke, flame-retardant materials, CMP cables are designed to resist ignition, prevent flame propagation, and produce very low smoke and toxicity levels - far superior to standard halogen-free cables. However, due to their higher cost, CMP cables are often used only in specific high-risk zones rather than throughout an entire cabling system.

Because of their exceptional safety performance, CMP cables are mandatory in plenum spaces and areas that demand high fire protection standards, such as office buildings, hospitals, schools, and public facilities.

3.4 CMX-rated ethernet cables

CMX (Communications Limited Purpose) ethernet cable meets the lowest level of fire resistance requirements. It is standardized according to the UL 1581 VW-1 flame test, which evaluates a cable’s ability to resist fire under practical installation conditions.

CMX cables typically feature a Linear Low-Density Polyethylene (LLDPE) outer sheath, which is PVC-free. This material provides excellent protection against UV radiation, moisture, and extreme temperatures, ensuring long-term durability and stable performance in harsh outdoor environments. A CMX-rated cable is therefore an ideal choice for outdoor applications where environmental protection is critical.

Thanks to its robust and weather-resistant construction, CMX cable is suitable for installation along building exteriors or in areas frequently exposed to outdoor conditions. It offers a reliable and safe network connection for outdoor environments, maintaining consistent performance and long service life.

Some CMX cable products from HELUKABEL include: HELUKAT® PROFInet C CAT.5e SF/UTP PUR CHAIN (800655), HELUKAT® 250S CAT.6 CMX SF/UTP PUR CHAIN (803387), HELUKAT® 500IND CAT.6A S/FTP PUR STATIC (11007778), HELUKAT® 600T CAT.7 SF/FTP PUR TORSION (805828).

4.2 Practical applications of each ethernet cable type

• CMP cables are highly recommended for most commercial or industrial wiring needs that demand the highest fire safety standards. These cables are specifically designed for plenum spaces - areas with circulating air, such as HVAC systems, drop ceilings, or raised floors.
• In residential and standard building projects, CMR cables are a popular choice thanks to their superior flame-retardant capability compared to CM cables. They are particularly suitable for multi-story buildings, offering enhanced safety while maintaining flexibility for various installation types.
• CM cables are sufficient for basic indoor networking applications, such as upgrading wired connections for TVs, gaming PCs, or home entertainment systems. For these purposes, CM Ethernet cables are a safe and cost-effective solution.
• CMX cables are the optimal choice for outdoor installations, as they feature UV resistance, moisture protection, and temperature tolerance. These properties ensure long-term performance and stability even under harsh weather conditions.

5.2 Is UV resistance an additional requirement for CMX ethernet cables?

CMX cables are designed for outdoor environments and have a basic level of UV resistance, but they are not equivalent to “Sunlight Resistant” (SUN RES) cables.

• According to UL 444, CMX cables undergo a 300-hour sunlight exposure test, which ensures reliable performance in standard outdoor conditions.
• In contrast, “SUN RES” cables have passed a 720-hour test, making them more suitable for direct sunlight exposure over long periods, such as on rooftops or unshaded outdoor installations.

In other words, CMX cables meet basic outdoor standards, while SUN RES cables provide enhanced UV protection for harsher sunlight conditions.

Some of HELUKABEL's Ethernet cable products feature high UV resistance (SUN RES), such as HELUKAT® 500IND CAT.6A S/FTP PVC STATIC (11007776), HELUKAT® 500IND CAT.6A SK S/FTP PVC STATIC (803693), HELUKAT® 500IND CAT.6A S/FTP PVC FLEX (11023769), HELUKAT® 250IND CAT.6 SF/FTP PVC STATIC (11017904), HELUKAT® 100T CAT.5e S/UTP PUR TORSION (802186), HELUKAT® PROFInet B CAT.5e PLTC-ER SF/UTP PVC FLEX (11018959), HELUKAT® PROFInet B CAT.5e SF/UTP FRNC FLEX Cca (11027770).

In addition to ethernet cables, some HELUKABEL bus cable products also achieve CMX and CMG ratings, such as:

• Profibus L2 (80384), Profibus SK (81903)
• CAN-BUS 0.50mm² ( 803722)
• SafetyBUS (800652)
• FOUNDATION™ (803354)
• A-BUS TPE, UL CMG (805693)
• DeviceNet™ (800683)
• Other bus cables