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What do you know about mineral-insulated cables?

Mineral cables generally refer to mineral-insulated cables, which can also be categorized into mineral-insulated cables and mineral fire-resistant cables within the industry.

A mineral-insulated cable is a type of inorganic material cable. The outer layer consists of a seamless copper sheath, and between the sheath and the metal conductor core lies a layer of highly compacted magnesium oxide (MgO) insulation. Depending on their specific applications, mineral-insulated cables are classified into: wiring cables, heating cables and heating elements, thermocouple cables and compensating cables, as well as special-purpose cables.

1. Operating Characteristics of Mineral-Insulated Cables
Safety
Mineral-insulated cables are made of copper and magnesium oxide (MgO). The melting point of copper is 1083°C, and that of MgO is 2800°C. Therefore, the cable structure remains intact at temperatures below 1000°C. In the vast majority of scenarios, it will not disintegrate due to melting or burning, nor will it spread fire. The insulation layer is made of inorganic materials that do not emit any smoke or toxic gases. In contrast, traditional cables (including flame-retardant, low-smoke low-halogen, low-smoke zero-halogen, and their corresponding fire-resistant cables) will emit smoke and harmful gases when ignited, exposed to fire, or subjected to long-term overloading that damages the insulation.
Fire Resistance
Currently, commonly used PVC cables (standard, flame-retardant, and fire-resistant types) have a maximum operating temperature of 70°C. Exceeding this temperature accelerates insulation aging and shortens service life, potentially leading to fires. According to the British BS 6387 standard for fire resistance testing of cables, only mineral-insulated cables can pass the following three tests:
C: Flame at 950°C for 3 hours.
W: Flame at 650°C with water spray for 15 minutes.
Z: Flame at 950°C with mechanical impact every 30 seconds.
Meanwhile, domestic fire-resistant cables (NH-VV) can only pass the Class A test in the GB 12666.6-90 standard: flame at 950°C for 90 minutes. Most fire-resistant cables on the market can only pass the Class B test: flame at 750°C for 90 minutes.
High Current-Carrying Capacity
The normal operating temperature of mineral-insulated cables can reach 250°C. IEC 60702 specifies a continuous operating temperature of 105°C, which takes into account the terminal sealing materials and safety requirements. Even so, its current-carrying capacity far exceeds that of other cables because MgO powder has a better thermal conductivity coefficient than plastics. At the same operating temperature, it offers a higher current-carrying capacity. For circuits above 16mm², one cross-sectional size can be reduced. For areas where human contact is not permitted, two cross-sectional sizes can be reduced.
Waterproof, Explosion-Proof, and Corrosion-Resistant
The cable features a highly corrosion-resistant outer sheath made of low-smoke, zero-halogen, and highly flame-retardant materials (a plastic outer sheath is only required in specific environments with chemical corrosion). The conductor, insulation, and sheath form a tightly compacted solid structure. This not only prevents intrusion from water, moisture, oil, and certain chemicals but also makes it suitable for wiring in hazardous locations and for connecting various explosion-proof equipment and devices.

2. Features and Applications
Compared to organic cables, mineral-insulated cables offer superior high-temperature resistance, fire resistance, explosion-proof performance, and non-combustibility (capable of continuous long-term operation at 250°C and short-term operation for 30 minutes under extreme conditions of 1000°C). They also boast high current-carrying capacity, small outer diameter, high mechanical strength, long service life, and generally do not require an independent grounding conductor.
Mineral-insulated cables are widely used in nuclear power plants, metallurgy, chemical engineering, mines, aerospace, high-rise buildings, airports, docks, and subways, as well as other crowded places. They are used to ensure power supply to critical fire protection equipment during emergencies, including fire water pumps, fire elevators, critical loads, emergency evacuation indicators, and smoke prevention and exhaust systems.

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