Everything You Need To Know About MI Cable

MI cable ( Mineral insulated cable) is an electrical cable known for its durability and reliability in extreme conditions. It consists of copper conductors inside a copper sheath, with magnesium oxide (MgO) powder of > 99.0% as the insulation. Other names for this type of cable include magnesium oxide or fireproof cable.

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This unique construction provides several advantages:

1. High temperature resistance: MI cables can withstand high temperatures up to  °C, the melting point of the copper conductor. The magnesium oxide (MgO) powder insulation can actually withstand temperatures up to °C.
2. Fire resistance: The non-combustible materials used in MI cables ensure they maintain functionality even during a fire, making them ideal for critical circuits in buildings. The cable is fire-resistant in temperatures of 950 °C for 180 minutes.
3. Moisture resistance: The solid copper sheath protects against moisture ingress, making these cables suitable for wet or corrosive environments.
4. Durability: MI cables are highly resistant to physical damage due to their robust construction.
5. Compact size: The lack of organic insulation materials allows MI cables to have a smaller diameter than other cables with the same current-carrying capacity. The cable has a higher carrying capacity than other cables of this size.
6. MI cable is also smoke-free, halogen-free, and resistant to radiation.

MI cable construction

The construction of Mineral Insulated (MI) cable is unique and consists of the following components (inorganic compounds):

1. Conductor:
• Material: Copper (or sometimes other metals like stainless steel for specific applications).
• Number of conductors: Typically single or multiple solid conductors.
2. Insulation:
• Material: Magnesium Oxide (MgO) powder.
• Properties: MgO is an inorganic material that provides excellent electrical insulation and high-temperature resistance.
3. Sheath:
• Material: Copper (most common) or sometimes stainless steel for additional corrosion resistance.
• Purpose: The sheath provides mechanical protection and acts as an electrical shield. For environments requiring additional protection against corrosion, stainless steel or other materials can be used for the sheath.

Applications of MI cables

1. Fire protection systems

• Fire alarm systems: Ensuring alarm systems remain operational during a fire. This includes fire alarm systems in high-rise buildings.
• Emergency lighting: Maintaining power to emergency lighting circuits to guide occupants safely during emergencies and ensure the lighting is functional during the fire.
• Sprinkler systems: Powering the control systems of fire suppression sprinklers.

2. Power distribution in large-capacity electrical equipment

• AC units and water pumps that pass through the building fire compartment.
• Elevators, roof ads, and landscape lighting equipment in elevator rooms.
• Power distribution in large shopping malls.

3. Industrial heating

• Heat tracing: Providing consistent heat along pipelines to prevent freezing or maintain fluid viscosity.
• High-temperature furnaces: Used in industrial furnaces and kilns where temperatures exceed the capabilities of conventional wiring.

4. Power generation and distribution

• Nuclear power plants: Withstanding high radiation levels and extreme temperatures in nuclear facilities, including safety critical systems. It is also used for testing, monitoring, and controlling temperatures.
• Power stations: Ensuring reliable power distribution within power generation plants.

5. Hazardous locations

• Chemical and petrochemical plants: Operating in corrosive environments with explosive atmospheres and high-temperature environments like furnaces and kilns.
• Oil and gas industry: Used in offshore rigs and refineries where high reliability and safety standards are required.
• Used in environments where explosive gases, dust, or vapours are present, ensuring safe and reliable electrical connections.

6. Building and construction

• Critical infrastructure: Wiring in hospitals, airports, tunnels, and other critical infrastructure.
• Historical buildings: Retrofitting old buildings with fire-resistant wiring without compromising architectural integrity.

7. Transportation

• Railways and subways: Providing reliable power and control wiring in underground and elevated transit systems, as well as lighting systems.
• Marine applications: Used in ships and offshore platforms where exposure to harsh marine environments and corrosion is common. It is also used to connect warning systems at sea and on oil tankers in extreme conditions.

8. Specialized equipment

• Medical devices: Ensuring the reliability of sensitive medical equipment and systems.
• Instrumentation and control: In precision instruments that require stable and reliable electrical connections.

9. Renewable energy

• Solar power plants: Used in solar power installations where reliability and longevity are crucial.
• Wind turbines: Providing power and control wiring for wind turbines in harsh and varying weather conditions.

10. Data centers

• Ensuring the integrity and reliability of uninterrupted power supply to critical data centre infrastructure, minimizing the risk of downtime due to fire or other hazards.

11. Military and defence

• Weapon systems: Used in critical defence systems where high reliability under extreme conditions is required.
• Field operations: Providing robust and reliable power in field-deployed equipment and temporary installations.

12. Industrial Thermocouples

Where is MI cable prohibited?

While not directly prohibited, MI cables are not suitable for:

• Flexible, temporary, and moving installations. MI cables are rigid and difficult to install in flexible environments.
• General residential use: While MI cables are excellent for specific critical applications, they are typically not used for general residential wiring due to cost, installation complexity, and other suitable alternatives.

Nassau National Cable provides a range of MI cables.

Author Bio

Vita Chernikhovska

is a dedicated content creator at Nassau National Cable, where she simplifies complex electrical concepts for a broad audience. With over a decade of experience in educational content and five years specializing in wire and cable, her work has been cited by authoritative sources, including the New York Times. Vita's popular series, such as 'What is the amp rating for a cable size' and 'How to wire different switches and appliances,' make technical information accessible. She also interviews industry professionals and contributes regularly to the wire and cable podcast.

Mineral insulated cable stands out for its impressive performance in extreme conditions. Often overshadowed by the more common PVC and rubber insulated cables, these rugged cables play an irreplaceable role. We will we'll take a comprehensive look at their construction, applications, and manufacturing processes, as well as their advantages and disadvantages. Let us unravel the mystery of MI cables.

What is mineral insulated cable?

Mineral insulated cable, also known as MI cable, MICC cable, or pyro cable, is an electrical cable using copper sheath to wrap the copper core and insulated with magnesium oxide powder; commonly used in high-temperature or harsh environments. Cable that adopts metal instead of copper sheath wrapped cores are known as mineral insulated metal sheathed cable (MIMS cable).

Mineral-insulated copper-clad cables are known for high-temperature resistance and durability and are commonly used in medium-voltage and high-voltage applications. Dense powdered magnesium oxide imparts MI cable excellent thermal endurance, enabling continuous operation above 250°C and resistance to corrosion and UV rays. The metal sheath of the cable can sometimes be used as a grounding circuit to simplify the wiring process. Compared to non metallic wire, MI wire is more robust and resistant to physical damage, making them durable even in harsh environments.

Next, Let's take a look at the specific applications of mineral insulated cables.

What is mineral insulated copper cable used for'

Mineral insulated copper cables are used in a variety of applications due to their high fire resistance, superior electrical properties, and durability. Some of the main uses include:

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1. Fire safety systems: Fire alarm systems, emergency lighting systems, and other safety systems that need to continue operating during a fire often utilize MI cables due to their ability to ensure that crucial communication remains intact in extreme temperatures. Cable with a red outer coating is usually used for fire alarms.
2. High-Temperature Environments: MI cables also find extensive use in high-temperature environments where conventional cables may fail, including furnaces, ovens, kilns, ceramic firing, iron and steel metallurgy, and even nuclear reactors where temperature resilience and nuclear radiation resistance are paramount. Furthermore, in construction and building services, MI cables are used for power supply circuits and heating systems.
3. Critical power supply: In places where power supply is critical, such as hospitals, data centers, and airports, MI cable is often used due to its durability and reliability.
4. High-rise buildings and public venues: MI cables are often used in high-rise buildings, theaters, schools, parking lots, and other public venues that require reliable emergency systems. In residential buildings, MI cable sometimes cab be used as service entrance cable.
5. Transportation Systems: MICC cables are used in transportation systems, such as tunnels, airports, and underground railways. In a famous example, during a fire in the Channel Tunnel connecting Britain and France in , installed mineral-insulated cables still provided emergency lighting for evacuating passengers even after the reinforced concrete and welded steel rails had been burned.
6. Chemically active or wet environments: The waterproof and corrosion resistance nature of MI cables also makes them suitable for applications where moisture or chemically corrosive is a concern, such as in underground systems, outdoor lighting installations, shipbuilding, and chemical processing plants.

Depending on the specific application, there are various mineral insulated cable sizes and specifications. And through the above typical applications of MI cables, we can summarize their key advantages and disadvantages.

Advantages and Disadvantages of Mineral Insulated Cable.

Just like everything has two sides, mineral insulated cables naturally have advantages and disadvantages, analyzed as follows:

Advantages:

• High Temperature Resistance: Mineral insulated cables comply with British BS fire safety standards, with a continuous operating temperature of 250 degrees Celsius, and can supply power for 3 hours at up to degrees Celsius.
• Electrical stability: Mineral insulated cable exhibits high insulation resistance and low capacitance to minimize capacitive coupling and charging currents, resulting in precise signal transmission and stable power delivery.
• Fire resistance: The mineral insulation utilized in MI cables is inherently noncombustible and will not propagate flames in the event of a fire. Additionally, it prevents the spread of harmful gases and chemicals produced when conductors or other components burn.
• Large carrying capacity: Mineral Insulated cables are capable of transmitting higher currents than ordinary cables of the same size, and can withstand high overload currents for short periods without causing serious damage.
• High Durability: Mi cable conductors are embedded in the mineral insulation, the cable is less susceptible to cracking and abrasion; and the metal sheath provides excellent mechanical protection, thus increasing the durability of MI cables in harsh environments.
• Electromagnetic Shielding: The metallic sheath of the cable acts as an electromagnetic shield to prevent interference in signal transmission, which is essential for critical applications requiring maintaining signal integrity, such as industrial automation and control systems.
• Long Service Life: The materials used in MI cables (copper and magnesium oxide) are naturally resistant to aging and have a service life of over 100 years.

While MI cables offer numerous advantages, it's essential to acknowledge their limitations.

Disadvantages:

• Cost: MI cables are typically more expensive than PVC cables, which can be a limiting factor for limited-cost projects.
• Installation complexity: MI cable installation and termination require special termination kits and training, which can add to the overall cost and time of the project.
• Limited Flexibility: MI cables are quite rigid due to their construction and therefore have limited flexibility, making it difficult to install in confined spaces or around corners.
• Quality Control: MI cables are difficult and costly to manufacture, and products from small factories may have quality problems. That's why you should choose a reliable mineral insulated cable company, like ZW Cable.

In summary, MI cables offer unique advantages, particularly in high-temperature and critical applications, but their higher cost and limited flexibility may render them less ideal for specific applications. When cabling, the advantages and disadvantages of MI cables must be carefully weighed to make an informed decision.

How is mineral insulated cable made?

The manufacturing process for MI cables requires precise engineering due to their intricate construction. First, copper or alloy conductors are arranged in the desired configuration and enclosed within a seamless copper sheath (or stainless steel or alloy, depending on the application). The space between the conductors and sheath is then filled with highly compressed magnesium oxide powder which serves as the insulator. This powder undergoes vibrational compaction to achieve a dense, uniform insulation layer.

Once the cable assembly is completed, it goes through a process known as annealing, which involves heating the cable to remove residual stresses created during the processing of copper parts. Annealing also removes trace moisture from the magnesium oxide, optimizing its insulating properties.

After that, the cable undergoes a series of stretching and intermediate annealing cycles. The stretching reduces the cable diameter to a specified size. Intermediate annealing restores ductility and prevents conductor breakage. Toward the end of the manufacturing process, MI cable ends are usually sealed with casting compounds to prevent moisture ingress. And the outer sheath can be coated with LSZH for added protection.

Lastly, finished cables undergo rigorous testing to confirm the insulation resistance, dielectric strength, and other critical parameters of the cable meet the safety standards and industry standards. Stringent quality control is essential to ensure cables achieve performance expectations in demanding applications.

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Bottom Line.

In summary, mineral insulated cables stand out as a remarkable solution for electrical installations requiring high performance. The unique properties of mineral insulated cables, including resistance to high temperatures and corrosion, give them a clear advantage in terms of safety, reliability, and operation under demanding conditions.