CM, CMR, and CMP are three different fire-retardant cable and network cables defined by the National Electrical Standards (NEC), which belong to the UL standard flame-retardant cable and network cables, which can effectively prevent fires and ensure data center and personal safety. So what is the difference between these three fire-rated cables? This article will elaborate for you.
What is CM?
CM is currently the most commonly used flame-retardant grade of cable and network cable. It is flame-retardant based on halogenated chemicals. Its test standard is UL 1581. According to the definition, a small bundle of CM-level cable and network cables will burn within less than 5 meters. It will go out automatically.
At present, the outer sheath of CM-class cable and network cable is mostly made of PVC material, and the insulating layer is made of high-density PE material, which emits toxic halogens, smoke and a lot of heat when burned. CM-level cable network cables are generally used for horizontal wiring on the same floor, and are commonly found in areas such as the United Kingdom, Asia and Australia.
What is CMR?
The safety of the CMR fire rating ranks second. It is mainly achieved by increasing the ignition point of the cable (about 300°C) to achieve the purpose of non-flammability. Its test standard is UL 1666. In the definition, under the forced combustion condition of the fan, one The bundled CMR cable and network cable must be extinguished by itself within less than 5 meters of combustion.
At present, the outer sheath of the CMR cable network cable is made of high flame-retardant PVC material, and the insulation layer is made of high-density PE material. After being burned with flame, it will emit toxic halogenated gas (chlorine) and lead vapor, and the halogenated gas will quickly Consume the oxygen in the air to extinguish the flame. CMR-class cable network cables are widely used in trunk line applications where the ventilation system is physically separated from the wiring system, that is, in the indoor vertical trunk line subsystem, which is common in Asia and Australia.
What is CMP?
CMP has the highest level of fire safety. It has perfect flame retardancy and will not emit a large amount of toxic smoke when burned. The CMP test standard is UL 910. According to the UL definition, a bundle of CMP cable and network cable must be extinguished within less than 5 meters of the combustion under the condition of forced intensive combustion of the fan.
The outer sheath of the CMP cable network cable is made of fluorine material (such as PTFE polytetrafluoroethylene, FEP fluorinated ethylene propylene), which has high decomposition temperature and high ignition point. Since the CMP cable network cable uses Teflo-based chemicals, it can prevent the spread of combustion and minimize the smoke and toxins emitted. Even in the event of a fire, the building will not be filled with a large amount of smoke or hazardous toxins emitted by the burning of the cable network cable. Therefore, CMP-class cable and network cables are used in air return pressurization systems used in ventilation ducts or air handling equipment, commonly found in Canada and the United States.
CM VS CMR VS CMP: What is the difference?
After the above introduction, you must have discovered the difference in fire rating, burning situation and outer sheath material between CM/CMR/CMP. In addition, they have differences in price, application area, and substitution.
1. The price difference
Since the outer sheaths of the CM cable network cable and the CMR cable network cable are made of PVC material, and the CMP cable network cable is made of fluorine material, the price of the CM cable network cable and the CMR cable network cable is cheaper than the price of the CMP cable network cable.
2. Different application areas
Under normal circumstances, CM cable is used for medium and horizontal wiring in other environments other than building elevators and air-filled rooms. CMR can be used for vertical wiring of building elevators and vertical channels. CMP is used for air ducts, air-filled rooms or other air. In the horizontal wiring in the circulation environment.
Under normal circumstances, CM cable network cable cannot replace CMR cable network cable and CMP cable network cable, but CMR cable network cable and CMP cable network cable can replace CM cable network cable.
How to choose CM/CMR/CMP cable network cable?
It can be seen from the above that the fire rating CMP>CMR>CM. So is it the most appropriate to choose CMP cable in practical applications?
Relatively speaking, CMP cable network cable is a good choice. Because CMP cable has the highest fire rating and safety, and is suitable for any type of cable and network cable requirements, if the building accidentally breaks into fire, the risk of inhaling toxic smoke is relatively low. However, considering the cost issue, it is not necessary to choose CMP cable network cable when wiring data center, such as vertical trunk system. At present, most data centers can be wired without air ducts. Therefore, CMR cable network cable It is also a good choice.
Related knowledge answers (what are PVC, LSZH, OPNR and ONFP?)
The above is the introduction of the fire rating of the cable and the outer sheath material. The fiber optic cable also has a specific fire rating (OFNP/OFCP/OFNR/OFCR). Compared with the CMR/CMP copper cable fire rating, the flame retardancy is more. More to visit "The importance of fiber optic cable sheath material and fire rating and how to choose".
Outer sheath material advantages
PVC (polyvinyl chloride) has good mechanical properties, high electrical insulation, strong flexibility, sturdiness and good flame retardancy, but has poor stability to light and heat, so it is more suitable for indoor optical fiber cables. Outer sheath material.
LSZH (low smoke and halogen free) has the characteristics of low smoke, low toxicity, low corrosion and high flame retardancy. As a safe and environmentally friendly material, LSZH is an ideal choice for indoor/outdoor installation; but the price is more expensive
Plenum is one of the main components of OFNR grade optical fiber cables. It has high flame retardancy and will not generate toxic or corrosive gas at extremely high temperatures. Fiber optic cables made of Plenum are the first choice for wiring in ventilation ducts or air recirculation booster systems used in air handling equipment.
Riser is one of the main components forming OFNR grade optical fiber cable, and its flame retardant performance is relatively
Plenum has a weak material and is non-toxic and corrosive gas specifications. Therefore, OFNR-grade optical fiber cables with Riser materials are usually used in building trunk lines and horizontal cable network cables.
OFNP/OFCP NEC standard flame retardant grade (pressurized grade), the highest grade. Assuming that a fan is used to force the flame to blow onto a bundle of flame-retardant (supercharged) fiber optic cables, the flame on the fiber optic cables will extinguish by itself within 5m, and non-toxic and non-corrosive gases will be generated.
The vertical level (trunk level) in the OFNR/OFCR NEC standard ranks second. Similarly, a fan is used to force the flame to be blown to the bundles of trunk-grade optical fiber cables. Although the flame will extinguish itself if it spreads within 5m, it has no smoke or toxicity specifications.