Mineral cables generally refer to mineral insulated cables, which can be divided into mineral fire-resistant cables in mineral insulated cable industry.

Mineral insulated cable is a kind of inorganic material cable. The outer layer of the cable is a seamless copper sheath, and between the sheath and the metal core is a tightly compacted magnesium oxide insulation layer. Mineral insulated cables can be divided into wiring cables, heating cables and heating elements, thermocouple cables and compensation cables, special cables, etc. according to different purposes.

1. Use characteristics of mineral cable

Security

Mineral insulated cables are made of copper and magnesium oxide. The melting point of copper is 1083 ℃ and that of magnesium oxide is 2800 ℃. Therefore, when the temperature does not exceed 1000 ℃, the cable structure will not have problems. Therefore, in most places, it will not be disintegrated due to melting or burning, nor will it spread kindling. The insulating layer of mineral insulated cables is made of inorganic materials, which will not emit any smoke and harmful gases. In contrast, traditional cables (including flame retardant, low smoke and low halogen, low smoke and zero halogen and their corresponding fire-resistant cables) will emit smoke and harmful gases when they are on fire, burned or damaged by long-term overload insulation.

Fire resistance

At present, the maximum service temperature of commonly used PVC cables (ordinary type, flame retardant type, fire-resistant type, etc.) is 70 ℃. Beyond this temperature, the aging of the insulation layer is accelerated, and the service life is shortened, leading to fire. According to the British BS6387 cable fire resistance characteristics test standard, only mineral insulated cables can meet the following three tests: A: open flame burning at 950 ℃ for 3 hours; B: open flame burning at 650 ℃ for 15 minutes; C: open flame burning at 950 ℃ for 30 seconds, hit with heavy objects; while domestic fire-resistant cables (NH-VV) can only meet the Class A test in GB12666.6-90 fire resistance test: open flame burning at 950 ℃ for 90 minutes. The fire-resistant cables produced by most manufacturers can only meet the Class B test; Open flame burning at 750 ℃ for 90 minutes.

Large current carrying capacity

The normal service temperature of mineral insulated cable can reach 250 ℃. IEC60702 stipulates that the continuous working temperature of mineral insulated cable is 105 ℃. This is in consideration of terminal sealing materials and safety requirements. Even so, its cutoff is far more than that of other cables. Because magnesia powder has a better conductor coefficient than plastic, it has a larger cutoff at the same working temperature. For lines with a diameter of more than 16mm, one section can be lowered, and for places where people are not allowed to touch, two sections can be lowered.

Waterproof, explosion-proof and corrosion resistant

Since the cable is sheathed with low smoke, halogen-free and high flame retardant material, which has high corrosion resistance (the plastic outer sheath is only required in the case of corrosion by some chemicals), the conductor, insulation and sheath are compact and solid. Therefore, it can not only prevent water, moisture, oil and some chemical substances from damaging, but also be used in places with explosion hazards and the connection of various explosion-proof equipment and apparatus.

2. Features and Uses

Compared with organic cable, it has the advantages of high temperature resistance, fire protection, explosion protection, non combustion (continuous long time operation at 250 ℃, short time operation at 1000 ℃), large carrying capacity, small outer diameter, high mechanical strength, long service life, and generally no need for independent grounding conductor. Mineral insulated cables are widely used in places with concentrated passenger flow, such as nuclear power plants, metallurgy, chemical industry, mines, aerospace, high-rise buildings, airports, docks, and subways, to ensure the power consumption of fire pumps, fire elevators, important loads, emergency evacuation instructions, and important fire protection equipment, such as smoke control and exhaust systems, in case of fire.