Mineral-insulated cables, also known as magnesium oxide cables, are copper-sheathed cables whose insulation material is magnesium oxide—a mineral-based compound—that protects the copper conductor. These cables boast exceptionally strong fire-resistant and insulating properties, which is why they are often referred to as fire-resistant cables. In the course of constructing fire protection systems, selecting the appropriate mineral-insulated cable is particularly crucial. It is essential not only to consider the physical and practical performance characteristics of these cables but also to take into account the specific requirements and construction standards of the fire protection system project itself. Electrical designers must thoroughly understand both the advantages and disadvantages of mineral-insulated cables and make informed decisions about their selection and application, thereby enhancing the overall quality of fire protection system construction. Against this backdrop, exploring the selection criteria and development trends for mineral-insulated cables used in fire protection circuits is of great practical significance.

I. Structural Principles of Mineral-Insulated Cables

Mineral-insulated cables primarily consist of the mineral material magnesium oxide and the metallic material copper. The magnesium oxide insulation material is used to tightly compact and encase the metal conductor within a seamless copper sheath, thereby providing comprehensive protection and integrating the conductor core with the outer jacket. In practical applications, the magnesium oxide insulation material has a melting point as high as 2,800 degrees Celsius. Under temperatures below this threshold, the cable’s insulation performance remains intact and unchanged. Meanwhile, the melting point of copper itself is 1,082 degrees Celsius; at temperatures below this threshold, the copper conductor within the cable remains undamaged, ensuring reliable power supply and transmission.

II. Performance Characteristics of Mineral-Insulated Cables

(1) Fire resistance. Mineral-insulated cables exhibit exceptional fire resistance and, in addition to meeting the relevant national standards, also satisfy the performance requirements for maintaining circuit integrity during a fire. In actual fire tests, after being exposed to intense flames, mineral-insulated cables remained intact, thereby confirming their outstanding fire-resistant performance.

(2) High-temperature resistance: Due to the extremely high melting points of the mineral material magnesium oxide and the metallic material copper, these cables not only offer fire resistance but also exhibit exceptional high-temperature endurance. Extensive practical experience has demonstrated that mineral-insulated cables can operate continuously in environments up to 250 degrees Celsius, with a service life exceeding 250 years. As such, mineral-insulated cables boast strong high-temperature resistance and excellent aging resistance, do not ignite or propagate flames, and represent an exceptionally safe cable product.

(3) Radiation resistance: During a fire, mineral-insulated cables, thanks to their inherently high melting point, remain unaffected by the fire and do not emit harmful gases or smoke. They also maintain high light transmittance, thereby providing crucial conditions for safe evacuation of personnel. Moreover, as an environmentally friendly cable, all its constituent materials are inorganic; after exposure to radiation, these materials remain unaffected, making such cables ideal for use in nuclear radiation environments and effectively shielding against both nuclear radiation and electromagnetic induction.

III. Economic Performance of Mineral-Insulated Cables

(1) Replacing PE wire with a copper sheath. In the manufacturing process of mineral-insulated cables, compared to conventional cables, this approach reduces the number of conductors and uses a copper sheath instead of PE wire, thereby saving on PE wire usage and subsequently lowering project costs, offering strong economic benefits.

(2) Extra-long service life. The actual service life of mineral-insulated cables is primarily determined by the oxidation rate of the copper sheath and is influenced by the actual operating temperature. In experiments, the oxidation rate of the copper sheath at 250 degrees Celsius was found to be equivalent to an oxidation period of 257 years, whereas the cable’s normal operating temperature is 105 degrees. This indicates that the service life of mineral-insulated cables far exceeds 257 years, meaning they will not need to be replaced within a century, thereby reducing engineering costs.

(3) Cable Cost and Expenses. Compared to other types of cables, mineral-insulated cables exhibit significant differences in both their structural design and materials. Based on available project cost information, the cost of mineral-insulated cables—calculated by cable cross-sectional area and length—is approximately 8% higher than that of polyethylene cables. However, under the same operating conditions, mineral-insulated cables can operate with two smaller cable sizes, thereby reducing costs associated with PE wires and metal cable trays. As a result, the overall construction cost is reduced by roughly 10%.

IV. Development Trends of Mineral-Insulated Cables for Fire Protection Systems

Based on the above analysis of the manufacturing structure, operational performance, and economic viability of mineral-insulated cables, in addition to their use in fire-fighting circuits, these cables hold extremely promising development prospects. Their development directions can be summarized as follows: First, for indoor electrical equipment in construction projects—during actual construction, mineral-insulated cables should be selected for power distribution to high-power electrical devices. Given that high-power equipment is prone to malfunctions and fires during operation—especially air-conditioning units or domestic water pump systems—the superior performance of mineral-insulated cables can ensure the safety and reliability of such large-scale electrical equipment. Second, for elevator machine rooms and indoor lighting within elevator shafts—given the extremely high safety requirements for operational reliability, mineral-insulated cables can be chosen to guarantee the safety and efficiency of power transmission. Moreover, in the event of a fire, these cables remain unaffected, thereby ensuring the personal safety of people inside the elevator.

Closing remarks

This article, through a study of the selection and development trends of mineral-insulated cables for fire protection systems, clarifies the manufacturing structure and operating principles of mineral-insulated cables. It also presents the operational and economic performance characteristics of these cables, analyzes future development directions, and thereby promotes the sustainable and healthy development of mineral-insulated cables.