Technical requirements for selection of flame retardant cables

 

Cable talk about flame retardant cable selection requirements

Flame-retardant cable characteristics: delay the spread of flame along the cable so that the fire does not expand. Due to its low cost, it is a large variety of cables used in fireproof cables. Whether the cable is laid or bundled, the spread of the flame can be controlled within a certain range when the cable is burned, so that the major disaster caused by the ignition of the cable can be avoided, thereby improving the fire level of the cable line. .

 

Dense cable

 

The flame retardancy of cables in a dense installation should meet the appropriate category requirements in accordance with the ‘Bundle wire and cable burning test method', as well as the cable configuration, the need to prevent catastrophic accidents and economic rationality.

 

1 In the same channel, it is not appropriate to arrange the non-flame-retardant cable and the flame-retardant cable in parallel.

 

2 In the following places or circuits that need to maintain power supply for a certain period of time outside the external fire, the cable to be applied should be fire-resistant or use a fire-resistant cable. (such as fire, alarm, emergency lighting, DC power supply for interrupter operation and safety circuit for emergency shutdown of generator set)

 

3 computer monitoring, dual relay protection, security power supply and other dual-circuit combination one of the same channel is not isolated from each other.

 

2. Mingshi cable implementation of fire protection

 

1 When the number of cables is small, fireproof coatings, tapes can be applied to the cables or the cables can be placed on the refractory tubes.

 

2 When there are many cables in the same channel, it should be laid in the refractory tank, and the power cable should be ventilated. In the environment without flammable dust, the semi-enclosed type can be used. When the cable protection section is laid on the bridge, the cable protection section is not long. A fire retardant bag can also be used.

 

3 In the case of oil tank areas, important wooden structure public buildings, high temperature places and other high fire resistance requirements, and installation and economic performance acceptance, non-combustible mineral insulated cables may be used.

 

4 Self-contained oil-filled cables shall be laid in public corridors, passenger tunnels, bridges, etc., where fire prevention treatment is required.

 

5 Close to the cable trench of oil-containing equipment such as high-voltage current, voltage transformer, etc., it is advisable to make the trench cover of this section dense.

 

3. Intensive places

 

1 In the cable-intensive or closed passages with high safety requirements, an automatic fire detection and alarm device suitable for environmentally reliable operation shall be provided.

 

2 The oil supply system of the oil-filled cable shall be provided with an automatic fire alarm and locking device that can reflect the fuel injection status.

 

3 Cable-intensive parts of underground public facilities, places with high security requirements such as terminal installations of multi-rechargeable oil cables, special fire-fighting facilities such as water spray fire extinguishing can be installed.

 

Since the 1980s, China has carried out scientific research results such as methods to prevent cable fire and flame retardation. It has been confirmed by ministerial level that it is related to the prevention of flame retarding effectiveness and combustion intensity, based on a series of combustion tests including physical simulation engineering conditions. The effectiveness needs to be renewed in recognition of the actual possible combustion temperature assessment. The power cables, home improvement wires, TV lines, control lines, special cables, fire-retardant cables, fire-resistant cables, low-smoke halogen-free cables, termite-proof cables, and mineral insulated cables produced by Zhujiang Cable are guaranteed by products. The cables are in line with the national (GB/JB) and International Electrotechnical Commission (IEC) standards, creating a wire and cable brand that customers trust and industry.

 

Talking about the selection of flame retardant and fire resistant cables

This paper introduces in detail the selection of flame-retardant cables, fire-resistant cables in buildings and their specific application sites, laying attention points, and also analyzes the difference between fire-resistant cables and flame-retardant cables, and puts forward the practical differences.

 

Author: Wu Lixin

 

  0 Preface

 

Cables and wires are the most widely used electrical products in electrical engineering. They function as electrical energy and are the main artery in buildings. As the size of the building is getting larger and larger, the complexity of the use function is increasing, and the power load is also rapidly increasing. At the same time as the power cable is used in a large number of applications, the electrical fire in China is also in a high trend. According to some data, electrical fires account for 30% to 40% of the total number of fires, which is more than a dozen percentage points higher than some developed countries, causing huge losses to the national economy, personal safety and people's property. Of course, there are many reasons for electrical fires, so I won’t go into details here. However, a large number of cables are also a fire hazard. Cable lines are the main cause of electrical fires and the first medium to spread fires. This is unquestionable. Therefore, the fire prevention of cable lines is an important part of electrical fire prevention, which has attracted the attention of designers. In particular, in recent years, electrical design specifications have been continuously improved, and various properties of flame-retardant and fire-resistant cables have begun to be widely applied. However, in some projects, some electrical design and construction personnel are confused about the concept of flame-retardant cables and fire-resistant cables, and do not understand the structure and characteristics of the two, resulting in the inability to correctly design and select cables according to power supply requirements, resulting in applications. Reasonable or incorrect, the installation of these two cables cannot be properly guided at the construction site. Therefore, a comprehensive and correct understanding of flame retardant and fire resistant cables is the primary condition for their proper selection.

 

1 flame retardant cable

 

1.1 Concept of flame retardant cable

 

A cable that is difficult to catch fire and has a flame retardant or retarded flame spread capability is a flame retardant cable. Its flame retardant performance has passed the test of GB/T 18380.3 (equivalent to IEC 332.3). The flame-retardant cable actually adds a flame retardant to the sheath material of the cable. After losing the external fire source, it has the ability to self-extinguish the flame and stop the flame. The cable is hard to burn and does not ignite. Many people mistakenly believe that the higher the oxygen index, the better the flame retardant performance of the cable, but it is not. The flame retardant properties of flame retardant materials are generally expressed by the oxygen index (Oxygen Idex, OI). The oxygen index is charged into a test device by a material test piece of a predetermined size, and the test piece is ignited by an igniter under a predetermined condition by a mixed gas of oxygen and nitrogen, and is determined to be maintained as a wax-like combustion. The percentage of the lowest oxygen concentration is expressed. Generally, the concentration of oxygen in the air is 21%. If a material cannot be ignited in air, the oxygen index of the material is >21%. The flame retardant grade of the cable is divided into four types: A, B, C, and D. A is the highest, and so on, but this level does not mean that the A-level oxygen index is the highest. The flame retardant rating of the cable is based on the non-metallic content of the cable in the same cable channel, ie the value of the oxygen index is independent of the propagation of the flame along the cable under combustion conditions. It is clearly stated in the relevant test standards that “the oxygen index can be used as the basis for quality control of similar products”. The relevant test data shows that even in the case of a single flame-retardant test cable (regardless of level), it may still be used in actual use. Flame retardant.

 

1.2 Construction and classification of flame retardant cables

 

According to different flame retardant materials used in flame retardant cables, flame retardant cables are classified into halogen-containing flame-retardant cables and halogen-free low-smoke flame-retardant cables.