Flexible mineral insulated cable

1、 Prospect analysis
Mineral insulated cables have been widely used in civil and public buildings, airports, subways, hospitals, ancient buildings, gas stations, shipyards, metallurgy and other fields abroad. It has only been applied in China in recent years. In 1999, the Ministry of Construction issued a construction atlas for mineral insulated cables, which recognized their reliability and will be widely recognized for their excellent performance in future engineering applications. This product is no longer primarily used for fire protection systems, but has become a development direction to replace products such as halogen-free low smoke cables, fire-resistant cables, flame-retardant cables, and bus ducts (with a capacity of 1500A and below) due to its cost-effectiveness.
2、 Product Usage
This product is mainly used for power transmission and distribution lines in special occasions such as fire prevention systems, emergency lighting, alarm systems, fire protection systems, high-temperature environments, installations, and facilities that require special safety (public places, high-rise buildings).
3、 Product Introduction
Traditional mineral insulated cable, abbreviated as MI cable, is an inorganic material cable. The outer layer of the cable is a seamless copper sheath, and there is a tightly compacted magnesium oxide insulation layer between the sheath and the metal core.
Flexible mineral insulated cableAlso known as embossed copper sheathed inorganic insulated cable, it is a new type of fire-resistant cable improved on the basis of rigid mineral insulated cable, mainly overcoming the disadvantage of limited production length of rigid mineral insulated cable.Flexible mineral insulated cableThere are already mature cable accessories, including terminals, wiring terminals, and intermediate connectors.
Nowadays, mineral insulated cables have a wide range of usage space in power distribution systems, and their fire resistance, durability, safety, reliability, convenient construction, and economy cannot be replaced by traditional power cables.
1. Fire resistance
According to statistics, the average proportion of electrical fires in China each year to the total number of fires and the resulting losses to the total losses are 27% and 40.6%, respectively. The number of electrical fires and the resulting losses belong to various types of fires. Among them, electrical fires caused by power lines account for as much as half, so choosing cables reasonably is an important link to avoid electrical fires or ensure the continuity of power supply for firefighting equipment even in the event of a fire, thereby extinguishing fires as early as possible and reducing losses.
The maximum operating temperature of commonly used polyvinyl chloride cables (ordinary, flame-retardant, fire-resistant, etc.) is 70 ℃. Beyond this temperature, the insulation layer ages faster, the service life is shortened, and fires can occur. Mineral insulated cables are made of copper and magnesium oxide or inorganic mineral synthetic mica tape. Continuous power supply for 180 minutes at flame temperatures ranging from 950 ℃ to 1000 ℃, and can approach the melting point of copper at 1083 ℃ in short or extraordinary periods. Therefore, in the vast majority of places, it will not disintegrate due to melting or combustion, let alone spread sparks.
According to the British BS6387 cable fire resistance test standard, only mineral insulated cables can meet the following three tests:
Burning with an open flame at 950 ℃ for 3 hours
B Open flame burning at 650 ℃, spraying water for 15 minutes continuously
Burning with an open flame at 950 ℃, hitting with a heavy object every 30 seconds
NH-VV can only meet the Class A test in GB12666.6-90 fire resistance test: open flame combustion at 950 ℃ for 90 minutes. NH-YJV can only meet Class B testing requirements; Burning with an open flame at 750 ℃ for 90 minutes.
2. Durability
The normal service life of a cable is determined by the integrity of its insulation layer. Cross linked polyethylene insulated cables have a longer lifespan among plastic cables. Under normal usage conditions, the longest service life is about 40 years, and the service life of PVC insulated cables is about 20 years. If overload occurs, the lifespan will be significantly reduced, and if a local fire occurs and the cable is damaged, it must be replaced. According to the normal service life of the building, cables need to be replaced at least twice or more.
The lifespan of mineral insulated cables depends on the oxidation rate of the copper sheath, which is related to their operating temperature. Even if used for a long time at 250 ℃, it takes 2.57 years to oxidize the copper sheath by 0.025mm. Even the smallest specification of mineral insulated cables (with a copper sheath thickness of 0.46mm) can have a lifespan of several hundred years, far exceeding the service life of buildings. In fact, cables cannot be used for a long time at 250 ℃. Even if the copper sheath oxidizes, its oxide copper oxide remains a good conductor with little impact on its performance. So, mineral insulated cables are a type of 'cable'.
3. Security
Traditional cables (including flame-retardant, low smoke and low halogen, low smoke and halogen-free, and their corresponding fire-resistant cables) will emit smoke and harmful gases when they catch fire, are burned, or suffer insulation damage due to long-term overload. The smoke of polyvinyl chloride insulated cables contains a large amount of CO, CO2, and chlorides, while the smoke of other cables also contains bromides, fluorides, and hydrogen sulfide, which pose significant hazards to humans. Mineral insulated cables are made of inorganic materials and do not emit any smoke or harmful gases.
4. Reliability
Mineral insulated cables are safe and reliable in terms of waterproofing and explosion prevention. Due to its seamless copper tube sheath, water, oil, and gas will not penetrate into the interior of the cable. PVC sheath can be installed in corrosive environments, and various protective measures ensure its safety. In terms of mechanical damage resistance, mineral insulated cables can withstand severe mechanical damage without compromising their conductivity, and can still function normally even when the outer diameter of the cable deforms to one-third of its original outer diameter; In terms of radiation resistance, because it is made of inorganic materials, the material itself is stable and can maintain high insulation resistance for a long time. However, the insulation layer of traditional cables is easily aged under strong radiation, and the insulation characteristics are reduced, which poses a danger.