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.

This unique construction provides several advantages:

1. High temperature resistance: MI cables can withstand high temperatures up to  1083°C, the melting point of the copper conductor. The magnesium oxide (MgO) powder insulation can actually withstand temperatures up to 2800°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.

• 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.

• 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.

• 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.

• 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.

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

• 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.

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

• 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.

• 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.

• 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.

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.