Common fire protection cable

In common cables, PVC sheathed power cables are superior to PE sheathed power cables in terms of waterproof performance, but under fire conditions, the harmful gases released by PVC far exceed those of polyethylene. Almost all cable manufacturers produce PVC sheathed power cables, of which only some manufacturers also produce polyethylene sheathed power cables.

Flame-retardant cables: Flame-retardant products can provide more than 15 times of escape time than non-fire-retardant products; materials fired by fire-retardant materials are only l/2 of non-fire retardant materials; heat release rate of fire-retardant materials is only non-resistance L/4 of the burning material; the total toxic gas volume of the combustion product, if expressed as the equivalent amount of carbon monoxide, the flame retardant product is only 1/3 of the non-fire-retardant product; the smoke production performance of the ordinary flame-retardant product and the non-fire-retardant product There is no big difference in the amount of smoke produced. Fire-retardant cable is divided into three categories according to GB12666.5-90 standard A, B, C, in the engineering design should choose A type flame retardant cable. Reducing the number of cables in the same fireproof partition (such as the same bridge or the same shaft) can help improve the flame retardancy of the cable.

Fire-resistant cables: According to the provisions of GBl2666.6, the fire test temperature is divided into two categories: A class is 950-1000 °C assessment time is 90 minutes B class is 750-800 °C assessment time is 90 minutes. That is, the cable can still be energized within 90 minutes when the external fire source is directly burned at 750-800°C (or 950-1000°C), and it is judged as a Class B or Class A fire-resistant cable.

Organic fire-resistant cables are wrapped around copper conductors with a mica fire-resistant belt (high temperature 800°C) as a fireproof layer, then extruded with a certain thickness of normal insulating layer according to different models, and finally the cable core filling layer and the outermost jacket and Ordinary cable. Inorganic type is also called mineral insulated or magnesium oxide insulated cable. The outer sheath is copper tube or special alloy tube. Magnesium oxide is used as insulating material between the outer sheath and the copper core conductor. The melting point of magnesium oxide is 2800. °C, the melting point of the copper tube (outer sheath) is 1083 °C, the special alloy tube can guarantee no deformation at 825 °C, so as long as the outer sheath is not damaged, the cable can work normally, and its fire resistance far exceeds the organic fire resistance cable. In the engineering design, do not easily request the use of Class A fire-resistant cables, because NH-YJV or NH-VV generally do not meet Class A requirements, and although the fire resistance of mineral insulated cables is excellent, the cost is much higher than that of ordinary fire-resistant cables. The requirements for construction are more stringent. In addition, since they are single-core cables, the relative N and PE spacings are different, and single-phase short-circuiting and grounding short-circuit impedance (reactance) are somewhat different.