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The structure, characteristics and selection of flame retardant and fire-proof cables

Information Source:Henan Huadong Cable Co., Ltd Release date:2014-03-10

Under what circumstances to use flame retardant cable? What the case with Fire Retardant cable? Application of what is the difference?

In recent years, the electric power system of fire accident in the global scope, because of the power cable fire caused proportional power interruption of the rising trend. In power plant, substation and stop the spread of the flame retardant cable large electrical equipment and cable laying large dense place, the fire-resistant cable to ensure uninterrupted power supply important loop becomes more and more important. While some electrical design of flame retardant cable and the fire-resistant cable concept confusion, structure and characteristics of the two who do not quite understand, resulting in not according to the power supply requirements for the selection of these two kinds of cable, design agency or supervision in the field can not correctly refers to the laying of the two cable guide. Therefore, comprehensively and correctly understand the flame retardant and fire is the primary condition for their proper.

1, fire retardant cable
Flame retardant cable is used: under stipulated test condition, sample was burning, in the removed from the test fire, flame spread only in a limited range, remnant spark or burning in a limited time can self extinguishing cable. Its basic feature is: in case of fire may burn out and can not run, but to prevent the spread of fire. Generally speaking, the cable in case of fire, can make the combustion limit in the local scope, does not produce spread, keep all sorts of other devices, to avoid further loss.

1.1 The structure characteristics of flame retardant cable
Structure of flame-retardant cable and cable is basically the same, the difference lies in the insulating layer, sheath, outer protective layer and its auxiliary materials (bag and filling) all or part of the flame retardant materials.

1.2 Classification of flame retardant cable
According to the cable flame retardant, flame retardant cable consists of halogen containing flame retardant cable and low smoke halogen-free flame retardant cable two categories.
Insulation, sheath, outer protective layer and the auxiliary material containing halogen flame retardant cable which (bag and filling) all or part of the polyethylene (PVC) halogen containing flame retardant material, it has good flame-retardant property. But in the cable combustion releases smoke and halogen acid gas, halogen acid gas corrosion damage to the electrical equipment around, rescue workers need to wear a gas mask, to close to the scene to put out the fire. Cable combustion to electrical equipment and rescue workers around the harm, is not conducive to fire fighting and rescue work, which leads to the two serious "".
Insulation, sheath, outer protective layer and the auxiliary materials and low smoke halogen-free flame retardant cable (bag and filling) in whole or in part using the crosslinked polyethylene containing no halogen flame retardant, flame retardant (XLPE) not only has the characteristics of better, but also in the cable burns without halogen acid gas is released, smoke the amount of the cable is also small, between the corrosive gas produced by the combustion of the cable are cable flame retardant and reduce the amount of halogen acid gas take eclectic method developed low smoke and low halogen flame retardant cable. The halogen content of it is about 1 / 3 of halogen containing flame retardant cable. The smoke is also close to the "low smoke" level.

According to the "Regulations" test method for wire and cable combustion, the flame retardant cable beam combustion test method of the assessment is divided into A, B, C3, among them a kind of cable the severe test condition, performance than B, C is better, the price is also the most expensive.

In order to realize the cable flame retardant cable or improve the flame retardant level, people developed extruded the so-called "oxygen barrier" or "fire insulation layer" as the packing or wrapping fire retardant bag (fire insulation layer) and new structure of the flame retardant cable, and the cable is called "oxygen (fire) layer" cable. Its main principle is to add the metal hydrate materials, also can achieve the low smoke and low halogen, low smoke zero halogen flame retarded and cable. However, the so-called "oxygen isolating layer" and "fire" is just a means to realize the cable flame retardant in the final analysis, it is a kind of flame retardant cable, it can reach the highest level is a flame retardant. Therefore, cannot take the flame retardant cable is called "oxygen barrier" cable, and can only say "oxygen barrier" cable is a kind of flame retardant cable.|

1.3 Note selection problem

The designer should design the selection and laying of cable according to the specific characteristics of fire retardant cable, and should pay attention to the following questions:

(1) because of halogen containing flame retardant cable (including flame retardant, low smoke and low halogen flame retardant cable) in the combustion will release the halogen acid is corrosive, greatly hinder the fire work so as to delay the time and increase the spread of fire, and should therefore be to design the low smoke halogen-free flame retardant cable in the densely populated public places. You can choose any kind of flame retardant cable population density in the small operation area.

(2) flame retardant cable is divided into A, B, C3, among them a kind of flame retardant cable performance than B, C is better, the price is the most expensive. Designers provide ordering list should identify the flame retardant cable category.

(3) from the appearance can not distinguish between flame retardant cable A, B, C class, only by manufacturer supply assurance, so in the design selection should carefully choose the cable manufacturer.

(4) the low smoke halogen-free flame retardant cable compared with halogen flame retardant cable, has the advantages of low corrosion, low smoke, but the electric properties and the mechanical properties decreased significantly, so the cable laying, low smoke halogen-free flame retardant cable should be a halogen containing flame retardant cable with a larger bend radius.

(5) in the cable laying design, not the non flame retardant cable and cable laying should not be tied, different flame retardant type flame retardant cable juxtaposed laying.

2, fire-resistant cable series

Fire resistant cable is: under stipulated test condition, sample was burned in the flames, still can maintain normal running performance in a certain period of time. Is its basic feature: cable can still maintain the normal work of the line for a period of time in the combustion conditions. Popularly speaking, in case of fire, the cable is not a safe combustion, loop. So the main difference between resistant cable and flame retardant cable is: normal power supply cables can maintain for a period of time at the time of the fire, and the fire retardant cable does not have this feature.

This characteristic determines the fire-resistant cable plays an important role in modern urban and industrial buildings, because once the fire happens, control, monitoring, guiding and alarm system power supply circuit must maintain normal work. Therefore, the cable is mainly used in the emergency power supply to the user the fire fighting equipment, fire alarm equipment, ventilation equipment, navigation lights, emergency power supply socket, emergency elevator power supply circuit.

2.1 The structure characteristics of refractory cable

Structure of fire-resistant cable and cable is basically the same, the difference lies in the fire-resistant cable with copper conductor conductor good fireproof performance (copper melting point is 1083 ℃), and the conductor and the insulating layer is added between the refractory layer. The refractory layer by layer mica tape wrapped into. Because the allowable working temperature of different cloud master with a large difference, so the key fire resistance cable is mica tape.

2.2 Classification of refractory cable

In Chinese ordinary fire resistant cable is divided into class A and B: B cable can at 750 ~ 800 ℃ flame and rated voltage withstand combustion of at least 90min and cable without breakdown (3A fuse not fuse). On the improvement of the refractory layer manufacturing process and increase the basic fireproof layer on the method and developed a type fire-resistant cable, it can be in 950 ~ 1000 ℃ flame and rated voltage withstand combustion of at least 90min and cable without breakdown (3A fuse not fuse). Fire performance of a fireproof cables are better than the B type.

In addition, mineral insulated cable is fire resistant cable is a good performance, which is composed of a copper core, copper sheathed, Magnesium Oxide insulating materials processing, referred to as MI (minerl insulated cables) cable. The cable is composed by inorganic refractory layer, and a refractory layer of ordinary fireproof cable is composed of inorganic and organic compound and into, so the refractory properties of MI cable than ordinary fire-resistant cable better and not due to the combustion and decomposition of the corrosive gas. MI cable has good fire-resistant performance and can work for a long time under the high temperature of 250 DEG C, and explosion-proof, corrosion resistance is strong, large carrying capacity, radiation resistance, high mechanical strength, small volume, light weight, long service life, smokeless characteristics. But the price is expensive, complex process, difficult construction, high requirement and economy in the tank area, important public buildings, timber structure high places and other refractory acceptable occasion, can adopt the good fire resistance cable.

2.3 Note selection problem

According to the specific characteristics of fire-resistant cable, designers should pay attention to the following problems during the design and selection of:
(1) when the fire resistant cable for cable tunnel, cable interlayer cable intensive, or located near the depot, pipe and other inflammable places, should first choose a type fire-resistant cable. In addition to the above situation and cable configuration number, can use B class fire resistant cable.
(2) power supply circuit fireproof cables are mostly used as emergency power supply, the normal work of fire. As a result of the fire when the ambient temperature is rising sharply, in order to ensure the delivery capacity, reducing the pressure drop for the line, power supply line is long and strictly limit the allowable voltage drop circuit, should be at least a fire-resistant cable section enlargement.
(3) resistant cable can not be used as high temperature resistant cable.
(4) for the failure probability of reducing cable joints in the fire accident, in the installation should minimize the amount of joints, in order to guarantee the circuit can work normally in the fire. If you need to do to make fire branch connection, joint processing.

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