Ethernet Cable Jacket Rating: CMR vs CMP vs CM vs CMX Cable

Updated: December 2, 2024

Nowadays, people are becoming increasingly aware of fire prevention. But it’s easy to overlook one such fire risk—ethernet cables. A cable with a low fire rating can cause a house to burn down. In the United States, Canada, and other North American countries, the common fire ratings of ethernet cables are CM vs CMR vs CMP. The UL standard specifies the fire rating of these cables in detail.

So, what is the difference between a CMX, CM, CMR, or CMP cable?The following describes the Ethernet cable sheathing level. I hope that your understanding and selection of fire-resistant cables will help.

Flame Retardant vs Fire Resistant Cables – What’s the Difference?

Fire-resistant cables can continue to operate for a specific period in the event of a fire. 2-hour fire-resistant cables can maintain circuit integrity and continue to operate under certain conditions, which is why they are also called circuit integrity (CL) cables. Fire-rated cables are made from materials that can withstand high temperatures, such as mica, glass, and ceramics. They are used in emergency and critical systems such as evacuation communication systems, emergency lighting, etc.

Fire-retardant cables prevent fire from spreading to new areas. They are not as strong as fire-resistant cables. They are usually made of flame-retardant chemical materials such as PVC, LSZH, FRPP, etc. Flame-retardant cables are used in residential or office buildings.

What is CMP (Communications Multipurpose, Plenum)?

This is a more demanding cable (Plenum Cable) in the UL fire protection standard.  the CMP cables are also referred to as “plenum-rated cable”. The applicable safety standard is UL910 or CSA FT6.

The insulation of the CMP cable is made of PTFE (Polytetrafluoroethylene), FEP (Fluorinated Ethylene Propylene), or low smoke PVC(Polyvinyl Chloride ), and the outer sheath is made of PVC. FEP is highly fire-resistant and can withstand temperatures as high as 800°C or more before it burns and disintegrates with smoke. This is several times higher than the usual halogen-free cable, which can withstand temperatures of up to 150°C. At the same time, FEP is also a highly efficient insulator.

This CMP cable is typically installed in ventilation ducts or air return pressurization systems used in air handling equipment. It is often used in buildings that require high safety standards, such as office buildings, hospitals, schools, etc.

What is CMR (Communications Multipurpose, Riser)?

This is the UL standard for Riser Cable. The applicable safety standards are UL1666 or CSA FT4.

Currently, the CMR network cable cable’s outer sheath is made of high flame retardant PVC outer network cable material. The insulation layer is high-density PE(Polyethylene ) material; after encountering flame combustion, it will emit poisonous halogenated gases (chlorine) and lead vapors; the halogenated gases will quickly consume the oxygen in the air to extinguish the flame.

CMR cables are generally used for vertical trunking indoors.CMX cables most often come in category option of Cat5e or Cat6

What is CM (Communications Multipurpose)?

This is the UL standard for general-purpose grade cables with applicable safety standards UL 1685 or CSA FT1.

The outer jacket of the CM network cable is mainly made of PVC, and the insulation layer is made of high-density PE. When burned, it emits toxic halogens, smoke, and much heat. It has specific flame retardant properties, but they are lower than CMP and CMR. CM network cable is suitable for general buildings with horizontal cable wiring. Generally, it is only used for horizontal cabling on the same floor, not vertical cabling on the floor.

What is CMX (Communications, Outdoor/Residential)?

This is the UL standard for Residential Cable (Restricted Cable), and the applicable safety standards are UL1581 VW-1 or CSA FT1. CMX Ethernet cables are primarily designed for outdoor use.

CMX cables are typically sheathed in LLDPE(Linear Low-Density Polyethylene), which is rain and UV-resistant or PE. compared with CMR, CM, or CMP cables, they are not fire-rated.,but CMX cables have more durability and impact protection.

This type cable has the lowest flame retardancy of almost no and is designed for single or small amounts of wiring. It has much lower flame retardant requirements than CM and CMR cables.CMX cables have the lowest flame retardant properties under fire conditions and can only prevent flame propagation from a single or small number of wires. Therefore, relevant fire codes should be followed when cabling to avoid cables passing through firewalls or fire breaks.

CMX vs CM vs CMR vs CMP Cable: What is the Difference?

Specifications	CMX	CM	CMR	CMP
Jacket Material	LLDEP	PVC; PE	PVC; PE	low smoke PVC; FEP
Compliance	UL1581 VW-1;CSA FT1	UL 1685; CSA FT1	UL 1666; CSA FT4	UL 910; CSA FT6
Fire Rating	CMX<CM<CMR<CMP	CM＜CMR＜CMP	CM＜CMR＜CMP	CM＜CMR＜CMP
Other ratings that will satisfy the requirement	CMP, CMR, CM, CMG	CMP, CMR	CMP	None
Application Scenarios	Outdoor, Residential	In-wall rated; permitted in 1-2 family residential riser applications, or in riser with raceway/fireproof shaft; not permitted in plenums.	All in-wall and riser applications are not permitted in plenums.	All in-wall, plenum, and riser applications.
Cable Price	The cost of a CMP cable is much higher than that of the others.
Priority	CM cables cannot replace CMR and CMP cables. CMR can be used in any non-plenum indoor space, while CMP can alternate all.

Some Related Terms: PVC and LSZH

When talking about Ethernet cables, PVC and LSZH are often mentioned. What do they refer to? These two terms refer to the chemical components used in producing Ethernet cables.

• PVC: PVC stands for Polyvinyl Chloride and is a commonly used sheathing material. Its advantage is that it is low-cost and flexible. Still, its disadvantage is that it releases smoke and toxic gases when it burns, making it unsuitable for ventilation systems.
• LSZH: LSZH, also known as Low Smoke and Halogen Free, as the name suggests, releases very little smoke and toxic halogen gases.LSZH cables are much more flame-retardant but are more expensive than PVC materials.

How to Choose the Suitable Ethernet Cable?

Ethernet cables with fire-retardant jackets, such as CM, CMR, and CMP cables, are typically used indoors. CMX is the least fire-retardant and is normally designed for outdoor use. CM cables can be used for general applications in residential buildings; CMR cables are recommended for vertical wiring within walls or between floors. CMP cables are preferred when it is necessary to route cables through ventilated room areas for commercial use.

	CMX	CM	CMR	CMP
General purpose	√	√	√	√
Risers	×	×	√	√
Use within the walls	×	×	√	√
plenum space	×	×	×	√
Outdoor applications/direct burial	√	×	×	×
Fire rating	CMP>CMR>CM>CMX

The safety of densely populated areas such as schools, hospitals, airports, and skyscrapers is essential and requires foolproof security, which CMP-rated cables can fulfill. In the event of a fire, the fire will not spread along the CMP cable to other spaces to ensure the safety of the entire venue personnel.

Ordinary home decoration and general business wiring can meet fire requirements with CM-grade cable. Environmental protection and safety have become increasingly popular in recent years, and many important places are also slowly using a higher level of CMR cable.

Another factor to consider is the cost of installation. Although CMP cables can be installed in any area, the high cost limits their use; CMP cables are the most expensive of these cables, while CM cables are the most cost-effective type. Choosing the right cable jacket is critical to obtaining optimal cable performance.

Conclusion

This article introduces the materials and usage scenarios of three kinds of flame retardant cables: CM vs CMP vs CMR, and CMX, a non-flame retardant cable limited to outdoor use or buried underground. It also makes a comparison table of them. We hope it will help you choose the right fireproof cable.

Optcore offers several types of Ethernet cables, such as Cat5e, Cat6, Cat6a, Cat7, and Cat8. These cables are available in CM/CMR/CMP cable jacket ratings. They are perfect for a wide range of network applications, such as offices, homes, data centers, and many other scenarios.

Read more

• OFNP, OFNR, OFNG, OFCG, and OFCP: How to Choose?
• What Is Plenum Cable? OFNP Cable Explained