The difference between heat-resistant cables and fire-resistant cables

There are great differences between Europe and America in the standard selection of fireproof cables for integrated wiring, and the focus is on whether to use halogen-containing fireproof materials or halogen-free "environmentally friendly" fireproof materials. In order to ensure the integrity of data in a fire scene, what conditions must our current fire-resistant cables meet, and why some fire-resistant cables can be called "fire-resistant cables" instead of so-called "heat-resistant cables", this article explains and introduces the above issues and industry trends one by one.

1 Introduction

The most valuable thing in network transmission is information rather than network equipment. There is such a news that a citizen's house caught fire and she escaped from the fire with only a drawer. People asked her what it was! So precious? She said that it was a photo of me from childhood to adulthood. Other things are valuable, but photos are priceless. If they are burned, they will be gone forever. It can be seen that information is non-renewable. Once lost, it will be gone forever. Therefore, people try every means to back up data through various means, transmit data through a stable network, and place them in a safe place. People gradually turn the integrated wiring system to resist external invasion and avoid external harm. Therefore, cable fire prevention has become its top priority.

People often say that fire and water are merciless. Since humans discovered fire, fire has not only accelerated the development of human civilization, but also brought destruction to human civilization. Many ancient civilizations were destroyed by fire. Similarly, fire can also burn the integrated wiring system and interrupt network transmission. At the same time, if the cable produces a large amount of toxic gas and smoke during the combustion process, it will have a great impact on the escape of personnel and even become a hidden danger to safety. Therefore, engineers from various countries are stepping up research on fireproof cables that are safer for data backup and personnel.

2 Fireproof Cable Types

At present, the widely used fireproof cables are mainly UL series flame-retardant cables and flame-retardant low-smoke halogen-free cables. Among the imported products, they mainly come from America and Europe. Since the fireproof cable standards in America and Europe are incompatible with each other and the fireproof ideas are very different, the client and the design institute are in a passive state when choosing products. They each have their own reasons, and finally they often choose according to the actual situation of funds.

UL flame retardant standards mainly include the following grades: CMP, CMR, CM, CMG, CMX.

1) Pressure boosting level - CMP level (air supply combustion test/Steiner air duct test Plenum Flame Test/Steiner Tunnel Test)

This is the cable with the highest requirements in the UL fireproof standard (Plenum Cable), and the applicable safety standard is UL910. The test stipulates that multiple samples are laid on the horizontal air duct of the device and burned with an 87.9KW gas Bunsen burner (300,000 BTU/Hr) for 20 minutes. The qualified standard is that the flame cannot extend beyond 5 feet from the front of the gas Bunsen burner flame. The maximum peak value of the optical density is 0.5, and the maximum average density value is 0.15.

This CMP cable is usually installed in the air return pressurization system used in ventilation ducts or air handling equipment, and is approved for use in Canada and the U.S. The flame retardant performance of FEP/PLENUM materials that meet the UL910 standard is better than that of low-smoke halogen-free materials that meet the IEC60332-1 and IEC60332-3 standards, and the smoke concentration is low when burning.

2) Mainline Grade - CMR Grade (Riser Flame Test)

This is a commercial-grade cable (Riser Cable) in the UL standard, and the applicable safety standard is UL1666. The experiment stipulates that multiple samples are laid on a simulated vertical axis and a specified 154.5KW gas Bunsen burner (527, 500BTU/Hr) is used for 30 minutes. The qualified standard is that the flame cannot spread to the upper part of the room 12 feet high. There is no smoke density specification for trunk-level cables, which are generally used for vertical and horizontal wiring on floors.

3) Commercial Grade-CM Grade (Vertial Tray Flame Test)

This is the General Purpose Cable in the UL standard, and the applicable safety standard is UL1581. The experiment stipulates that multiple samples are laid on a vertical 8-foot-high bracket and burned with a specified 20KW ribbon blowtorch (70,000 BTU/Hr) for 20 minutes. The qualified standard is that the flame cannot spread to the upper end of the cable and extinguish itself. UL1581 is similar to IEC60332-3C, but the number of cables laid is different. There is no smoke density specification for commercial-grade cables, and they are generally only used for horizontal wiring on the same floor, not for vertical wiring on the floor.

4) General Grade-CMG Grade (Vertial Tray Flame Test)

This is a general-purpose cable in the UL standard, and the applicable safety standard is UL1581. The test conditions of commercial and general-purpose cables are similar, and both are approved for use in Canada and the United States. General-purpose cables do not have smoke concentration specifications and are generally only used for horizontal wiring on the same floor, not for vertical wiring on the floor.

5) Home Grade-CMX Grade (Vertical Wire Flame Test)

This is the home-grade cable (Restricted Cable) in the UL standard, and the applicable safety standards are UL1581, VW-1. The test stipulates that the sample is kept vertical, burned with a test blowtorch (30,000TU/Hr) for 15 seconds, then stopped for 15 seconds, and repeated 5 times. The qualification standard is that the residual flame cannot exceed 60 seconds, the sample cannot be burned by more than 25%, and the surgical cotton pad at the bottom cannot be ignited by falling objects. UL1581-VW-1 is similar to IEC60332-1, but the burning time is different. This grade also has no smoke or toxicity specifications and is only used in home or small office systems where a single cable is laid. This type of cable should not be laid in bundles and must be sheathed.

Low Smoke Halogen Free Cable (LSOH)

As the name implies, low smoke halogen-free cables are cables that emit less smoke and do not contain halogen when exposed to fire. The principle of low smoke halogen-free cables is to prevent the cables from producing a lot of toxic gas and smoke when burning in flames, thereby preventing people from suffering serious casualties during burning and greatly improving the survival rate of people in fires.

The test requirements for low smoke halogen-free cables meet the following three requirements:

Flame retardancy requirements: Low smoke halogen-free cables must be flame retardant. There are two flame retardancy levels, which are required to comply with IEC60332.1 (single cable vertical combustion test) and IEC60332.3C (bundled cable vertical combustion propagation test). The flame retardancy requirements of IEC60332.1 use the flame retardancy requirements of ordinary cables, while IEC60332.3C has higher requirements and belongs to the flame retardancy requirements of the trunk level.

Smoke density requirement: Low smoke halogen-free cables must undergo a smoke density test. This is done by burning the cables in a confined space, and then testing the final indoor smoke density after the flames are extinguished. It is required that the light transmittance should be able to reach 60% in the presence of smoke, so that people can see the road in the smoke.

Toxicity requirements: There are several toxicity test methods, such as mouse test, etc. The halogen acid gas release test (for low halogen test) and gas acidity test (for halogen-free test) are used in low-smoke halogen-free cables. The test principle is to determine the halogen content by analyzing the gas generated by low-smoke halogen-free materials at high temperatures (800℃ and 935℃ respectively).

Some materials describe IEC60332.1 as equivalent to UL's CM level requirements (IEC60332.2 is a test method for thin-diameter cables, which means that the alternative test method used in 60332.1 testing cannot be used), and IEC60332.3C as equivalent to UL's CMR level requirements. In fact, the test methods of these four standards are not the same and cannot be directly compared.

In summary, two series of cables are formed, one is the American CMX high flame retardant cable (the American standard explicitly requires that CMX cable contain halogen to increase the temperature at which the cable decomposes); the other is the European FR/LSOH flame retardant/low smoke halogen-free cable.

3 Fire-resistant cable

In order to ensure the security of data, people hope that after a fire occurs, there will be enough time to retrieve all data before the entire network is paralyzed, and transfer them to a safe place to minimize the possibility of data loss. Therefore, in the cable standards, there is also a type of fire protection standard, called the "line integrity" standard. Its goal is to keep the cable line unobstructed in the fire scene, so that power and information can still be transmitted normally. Therefore, cables that meet the series integrity requirements are also called fireproof cables.

There are two common levels of fireproof cables:

Chinese standard: At 750℃, it can still continue to work for 90 minutes (E90).

German standard: At 800-850℃, it can still continue to work for 180 minutes (FE180).

Although the latest Chinese data center standard requires that all cables use CMP-grade integrated wiring cables, that is, they can still transmit data normally without being damaged at a temperature of 500°C, leaving a certain amount of time for emergency information backup, but they cannot meet the requirements of the national standard for fire-resistant cables and cannot be called fire-resistant cables.

Some wiring manufacturers claim that they are able to provide optical cables that meet the German fire-resistant cable standards, that is, they can transmit information normally for 180 minutes in a fire scene of 800℃-850℃. They can become backup optical cables for large data centers, and once a fire occurs, there will be enough time to complete data backup. Of course, it should be noted that the related power cables should also be fire-resistant power cables, otherwise if the power is burned out, the entire data backup will be impossible.

4Flame retardant, fire resistant, low smoke, halogen-free cable

The purpose of using flame-retardant cables is to help people escape smoothly in a fire, and the purpose of fire resistance is to ensure that data can be transferred to a safe place in enough time in a fire scene. Therefore, the most ideal cable is one that has both flame-retardant/low-smoke halogen-free properties and fire-resistant properties. Selecting low-smoke, non-toxic, halogen-free copper cables and flame-retardant, fire-resistant/low-smoke halogen-free cables that meet CMP grades can prevent the spread of fire in a fire scene and transmit data safely, with less smoke and no halogen.

5 Conclusion

With the continuous development of the integrated wiring industry, especially the rise of data centers, people pay more and more attention to data security. As the highway of information transmission, the ability of cables to resist sudden disasters during the transmission process has naturally become a hot research field for engineers from all over the world. Fire prevention, as the first of the "three protections" of integrated wiring, has become a top priority. If anyone wants to make a difference in the field of safe cables, then it is inevitable that he or she will become a leader in the research of cable fire prevention.