What is Mineral Insulated (MI) Cable? - Yifang Electric Group Inc.

Mineral insulated (MI) cable, also known as magnesium oxide cable or fireproof cable, is a copper core copper sheathed cable insulated by mineral material magnesium oxide powder.

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Mineral insulated cables have unparalleled advantages compared to other cables, such as fire prevention, large carrying capacity, mechanical damage resistance, halogen-free and non-toxic, explosion-proof, waterproof, corrosion resistance, long life, safety, overload resistance, high temperature resistance, termite resistance, and Rat bite, small cable bending radius, copper sheath as protective grounding wire, low cost and so on. Its use in the fire protection system provides a reliable guarantee for the normal operation of the fire protection system.

Mineral Insulated Cable Properties:

Structural principle: Mineral insulated cables are composed of mineral material magnesium oxide and metal material copper, and the magnesium oxide insulating material is highly compacted in the seamless copper sheath, forming a dense body together with the core and the sheath. The melting point of magnesium oxide insulation material is as high as °C. Below this temperature, its insulation performance will not change significantly, while the melting point of copper is °C. As long as the melting temperature of copper is not reached, the cable will not be damaged and can still continue to work. run.

Fire resistance: The fire resistance of mineral insulated cables meets the fire resistance time of 950 °C and 180 min specified in the product standard. Many fire scenes have also fully proved that after the fire, among all the cables, only the mineral insulated cables are still intact.

High temperature resistance, no aging: Mineral insulated cables can be used continuously for a long time at 250 ℃, with a life span of more than 250 years. Since the cables are all composed of inorganic materials, they are extremely difficult to age, and will not cause and spread fire, which is an essential Safe product.

Smoke-free, halogen-free, radiation-resistant: In the case of overload or fire, the mineral insulated cable itself will not release any harmful gas and smoke, and the light transmittance reaches 100%, which is very important for ensuring the safe evacuation of personnel under fire conditions It is very important; it can also ensure that houses and equipment are not damaged by acid gas. It is an environmentally friendly cable. Since the entire structure of the cable is made of inorganic materials, there will be no change after irradiation, so it is especially suitable for the environment of nuclear radiation; also due to the structural characteristics of the seamless copper sheath of the cable, it can provide very good shielding for electromagnetic induction Effect.

Large carrying capacity and strong overload resistance: For cables with the same cross-section, mineral insulated cables have higher carrying capacity than other types of cables due to their high thermal conductivity, good heat dissipation and higher operating temperature; Organic cables must be protected by bridges or sleeves in power distribution to prevent heat dissipation and reduce the ampacity of the conductors. In this way, under the same ampacity conditions, the mineral insulated cables can reduce the cross-sectional area by more than 1 to 2 grades compared with ordinary organic cables. use. In addition, the melting point of magnesium oxide, the insulating material of mineral cables, is °C, which can withstand more than 10 times the high current without being burned.

Overvoltage resistance: Overvoltage will break down the cable. For organic cables, the insulation at the breakdown point will be burnt to form a carbon path, making the cable scrapped; and even if the mineral insulated cable is broken down, it will be used as the oxidation of the cable insulation layer. Magnesium, the breakdown point will automatically solidify after melting, basically will not reduce the withstand voltage level of the cable, and the cable can still be used after passing the test.

Corrosion resistance and mechanical damage resistance: Copper has excellent corrosion resistance, and in most cases, no additional protective measures are required; in special cases, such as when used in some occasions that corrode the copper sheath of the cable , a layer of plastic jacket can be added outside the cable. Because the copper sheath of the cable has a certain strength and toughness, and the magnesium oxide is compressed by high strength during the cable processing, so when the cable is subjected to bending, flattening, and torsion, the cable core wire, the core wire and the sheath The relative position between remains unchanged, and no short circuit will occur.

Where to use mineral insulated cables?

1. Mineral insulated cables are used for power distribution of large-capacity electrical equipment in buildings, such as air-conditioning units, domestic water pumps, etc.; in places where the basement needs to pass through fire compartments, mineral insulated cables are used for power distribution, which can better reflect the superiority of fire-resistant cables sex.
2. All elevators, roof advertisements, and landscape lighting electrical equipment in the elevator machine room of the building shall use mineral insulated cables for power distribution.
3. Large shopping malls have access to power distribution rooms, and it is convenient to lay mineral insulated cables, so it is a good choice to use mineral insulated cables as distribution trunk lines.
   

How To Install MI cable?

1. After the mineral insulated cable is cut off, the saw end should be temporarily sealed to prevent moisture and moisture from entering the insulation layer.
2. When the cable passes through the expansion joint or settlement joint of the building, an expander should be installed, that is, the cable should be set in an S shape to solve the expansion and contraction problem of the cable.
3. The copper sheath of the mineral insulated cable must be grounded, and the section and connection of the grounding wire should also meet the standard requirements, and one end should be grounded.
4. Test the resistance immediately after the joints of each cable are installed, and test again 24 hours after passing the test to check the sealing condition of the intermediate joints.
5. The protective layer of the single-core cable will produce weak eddy current phenomenon under the action of gate alternating current. In order to prevent the accumulation of eddy current when multiple cables are used, different arrangement and laying methods can be used to reduce the influence of eddy current.
6. When the cables are laid vertically along the bridge frame, they can be fixed by binding copper wires. The steel cable clips can only be used to fix the three phases of a single-core cable together, and cannot be used for fixing a single single-core cable.
7. During the cable laying process or after the laying installation is completed, it is strictly forbidden to drag or collide the live welding wire on the cable to prevent holes in the copper sheath of the cable and cause moisture in the air to be absorbed by the magnesium oxide insulation , leading to a decrease in the cable insulation resistance.

Conclusion

With the successful development of mineral insulated cables, its scope of use will become more and more extensive. At the same time, the use of mineral insulated cables also protects the safety of people's lives and properties.

Mineral insulated cable, a copper sheath-wrapped copper conductor core, and magnesium oxide powder as an inorganic insulating material to isolate the conductor and the sheath of the cable, the outermost layer can be selected according to the need for an appropriate protection sleeve.

The Use And Characteristics Of Mineral Insulated Cable

Rigid mineral insulated cable was invented earlier, at the end of the 19th century. The Swiss engineer Arnold Francois Borel on the idea of mineral insulated cable, and received a patent in , -, France, and Britain into production to the rapid development.

China also developed in the s, began to be used in the military field, the mid-s began industrial production, and was gradually accepted by the construction field in full.

The invention of flexible mineral-insulated fire-resistant cable is relatively late. In the s was born in Switzerland at the Stout Cable Company.

Compared to the traditional BTTZ rigid mineral insulated cable. BBTRZ flexible mineral insulated cable is composed of copper stranded wire, mineral compound insulation, and mineral compound sheath.

It adopts a flexible structure, and the main materials are inorganic, which compensates for the defects of a hard structure, such as being easy to burn and toxic. It also has some advantages that other cables do not have. Such as fire resistance, high load capacity, shock voltage resistance, mechanical damage resistance, halogen-free, and non-toxic. And explosion-proof, waterproof, corrosion-resistant, long life, safety, overload resistance, high-temperature resistance, low cost, and other characteristics.

BBTRZ Fireproof Cable Structure

Cable conductor: There are multiple strands of copper wire twisted together, with good bending characteristics.

Insulation layer: It is made of mineral insulation material, which can withstand temperatures up to degrees.

Waterproof isolation layer: using polyethylene isolation material.

Mineral filling layer: inorganic mineral material with the advantages of fireproof, fire resistance, high-temperature resistance, and temperature insulation. Heat insulation developed by advanced nanotechnology at home and abroad.

Outer sheath: low smoke, non-toxic, or better, and higher plastic-type material with good anti-corrosion characteristics. Can be selected according to the requirements without the type of material (optional).

The Main Performance of The Mineral Cable

Flexibility

The conductor of the cable adopts the mature stranding technology, and the sheath is made of cross-linked inorganic material, a non-copper tube type. Therefore, not only lightweight and more flexible characteristics. It can avoid the wiring termination problems often encountered when designing and installing rigid mineral-insulated cables (BTTZ).

Fire-Resistant

Since the component materials of the cable are all mineral compounds. It determines the non-combustibility of the cable itself. The product complies with BS and IEC international standards and can withstand burning at 950°C for 3 hours under charged conditions. And guarantees the normal operation of the circuit. Therefore, it can remain unchanged even above the short circuit temperature.

Low Smoke

Smoke emission test according to IEC, the test transmittance reaches 80% or more (the standard is 60% ).

Halogen-Free

Since the cable insulation and sheath are inorganic compound materials, there is no usual PVC material. Therefore, even under fire conditions, there is no acidic gas dispersion.

Temperature Resistant

The cable can work at 125°C ambient temperature for a long time, replacing the use of low smoke and halogen-free flame retardant cables with a temperature resistance of 125°C. It can also work below °C for short periods in emergencies.

Corrosion Resistance

The mineral compound material used in the cable is more resistant to corrosion after irradiation and can be laid without any additional measures.

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High Load Capacity

Compared with the same cross-section of the cable. The flexible mineral-insulated fireproof cable can not only transmit higher currents but can also withstand larger overloads.

High Mechanical Strength.

Flexible mineral-insulated fireproof cables are made by cross-linking specially developed inorganic compounds through high-energy electron B-rays. The product conforms to BS and IEC international standards. It can withstand 30 consecutive impacts in 15 minutes at 950°C and under energized conditions. Comprehensively overcome the lack of mechanical characteristics of the cable due to the rapid deterioration of material aging characteristics.

Performance Comparison

General wire and cable because the insulation used is organic polymer materials, so it is very easy to carbonize under flame conditions, thus losing its role of insulation. As the main materials of flexible mineral insulation fire cable are all composed of inorganic minerals or mineral compounds, it does not cause fire itself, making it impossible to burn or fuel combustion. These materials generally have a high melting point of more than ℃, so the fire cable can play a normal function of power transmission even under flame conditions, which is a true sense of the fire cable.

The process structure of flexible mineral insulated fireproof cable products is the same as that of traditional cable, which successfully solves the numerous shortcomings of the product determined by the production process of magnesium oxide copper tube mineral insulated cable. The introduction of this product has become a milestone in the history of fireproof cable development and also accelerated the process of China’s cable technology research and development level to meet the international standard.

1. Traditional rigid mineral insulated cable characteristics

1.1. The copper tube drawing process makes a single continuous length limited; the installation process requires the continuous use of joints, increasing material and labor costs. And the a need for special treatment of the electrical properties of the joint. 2. 35 mm2 and above are all the same.

1.2. 35 mm2 and above are single-core cables, which require many installation procedures and are not conducive to the equalization of electrical parameters of each core.

1.3. The core bar type solid copper conductor is very hard, making its maximum cross-section usually 400 mm2.

1.4. Magnesium oxide powder as an insulation layer, prone to uneven thickness, a slight difference in the process will break through, rated voltage of up to 450/750V.

1.5. BTTZ cable constantly uses special connectors, so special treatment is required to ensure that the flame under the water is a spray to maintain power.

1.6. Once the copper tube shell is on fire, it is directly exposed to the fire temperature, 950°C + 50°C (the plastic outer sheath is instantly burned).

1.7. Metal sheath using a segmental drawing process, large cross-section of 400 mm2, single longest not more than 60 meters. Magnesium oxide pollution to the environment, high cost, and efficiency are difficult to improve.

2. Flexible Mineral Insulated Cable Characteristics

2.1. Improved insulation stability: not only retains the fire resistance characteristics of rigid mineral insulated cable, but also has the characteristics of not absorbing moisture, so the insulation is more stable.

2.2. Increased voltage resistance level: The voltage resistance level can reach V, thus reducing the impact voltage caused by the frequent start-up of inductors and inverter appliances. And accordingly, the service life of the line system is greatly improved.

2.3. Full series: according to the actual needs of users, it can be processed into single-core or multi-core structures, up to 96 cores. This can cover almost all specifications of power cables, flexible cables, and other building cable needs.

2.4. No intermediate joints: The use of mature stranding and cable formation technology, can be produced according to the user’s requirements of fixed length. Not only to reduce the cost of joints, but also to improve and achieve the consistency of the entire line.

2.5. Flexible and easy to install: Because of the traditional cable structure, such as stranded wire and cable formation. The cable is more flexible and does not require special terminal joints, which makes it easier to install and lay.

2.6. Space-saving: The availability of multi-core cables with large cross-sections and lengths eliminates the unnecessary waste of laying space due to multiple arrangements and intermediate joints.

2.7. Public welfare: Due to the improvement of the structure, a large number of minerals and mineral compounds are used, which not only saves copper, magnesium, and other resources, but also saves a lot of energy consumption accordingly, and the public welfare value is also very significant.

Application cases on super high-rise buildings

Case Introduction

Considering the slow reaction speed of people in high-rise buildings, as well as the panic and confusion caused by smoke and lack of electricity supply, the evacuation time of high-rise buildings is largely indeterminate. Therefore, the emergency line and fire alarm alert line become the most important lines in a fire, and the lines must be kept intact.

Liuzhou Diwang International Fortune Center is the tallest building in Guangxi Province and a landmark building in Liuzhou City. With a height of 303 meters and a 73-story all-steel structure. Due to the importance of the project, the fire protection system used Shengyu BBTRZ cable. The series of cables, due to the flexible mineral insulated cable, has a voltage resistance level is V. The design unit is based on the comparison of rigid mineral insulated cable (i.e., copper tube, magnesium oxide insulated cable) and various other types of structures of fire-resistant cables. Decided to use Shengyu BBTRZ flexible mineral insulated series of cables.

Installation and Laying

When the cable is laid openly, it should be supported by a cable bracket, hook, or metal lanyard along the whole length. The maximum span shall comply with the following provisions.

1. To meet the bearing capacity of the support pieces and ensure no damage to the outer layer of the cable and its cable core.

2. So that the cables can be configured neatly with each other.

3. To adapt to the working conditions of the arrangement requirements.

4. Directly support the cable with ordinary brackets (arm bracket), the allowable span of the hanger should be in line with the values specified in the table below.

Flexible mineral-insulated fire-resistant cables with a cross-sectional area of 1.5 mm2 to 600 mm2 for a single core and 1.5 mm2 to 300m2 for multiple cores. In the field of fire-resistant cables. Minimize the investment costs of the user unit and improve the safety and fire performance level of the building.

This type of cable can ensure emergency use after installation, and can also be used as a temperature-resistant 125 ℃ halogen-free flame retardant cable, or a fire-resistant cable. Because of the wide coverage of this series of cables. Not only overcomes the defects of rigid MI cables but also plays to the advantages of flexible MI cables. And provides a practical product for each key project. So that modern engineering in the electrical circuit to achieve a short circuit does not burn, burning does not affect the efficacy. The application cases used in this paper prove that not only the fire alarm and emergency life-saving circuits. And other fire performances can be successfully applied. In the case of high-density current and other special performance requirements, requirements can also be promoted and applied.

FAQ

Q: What is the temperature range of MI cable?
A: Typically –200°C to +950°C depending on the sheath material.

Q: Is the MI cable waterproof?
A: Yes, the metal sheath and sealed ends make it suitable for wet or submerged environments.

Q: Can MI cables be used outdoors?
A: Absolutely. Outdoor-rated mineral insulated cable is widely used in exposed or buried installations.