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.

Knowing the right wire for your project is essential. Knowing the right questions to ask will get you the wire and cable you need to kickstart your project. Kris-Tech's John Olguin (Southwest Regional Inside Sales) shares his insights into the 6 elements to look out for when looking for the right tray cable for your project.

1) AWG Wire Sizes

Tray cable comes in a variety of sizes. It is typical for a product to be listed with numbers representing gauge sizes; for example, VNTC Tray Cable 12-2 AWG or XPTC Tray Cable 14-10 AWG. The first number such as 12 or 14, specifies the gauge while the second #2 or 10 represents the number of current-carrying conductors. The wire can also have an extra ground number. VNTC Tray Cable 12-2 AWG would therefore mean a tray cable with 12-gauge, 2 insulated current carrying wires, plus a ground.

Here is an example of a VNTC tray cable spec sheet containing AWG sizes.

2) Shielding

A cable that is shielded contains insulated conductors encased in a standard conductive layer.  Shielded tray cables are normally more rigid and thicker compared to unshielded ones. Unlike unshielded cables, shielded cables require greater care when working with them. Shielded cables are often found in industrial settings where other equipment is likely to generate interference.

i) Shielded VNTC tray cable

ii) Unshielded VNTC tray cable

Tongda Product Page

3) Conductor Count

Conductor count is the number of insulated conductors in a cable. For instance, a red, black, white and bare ground is a three conductor and a red, black, white and green is a four conductor.
In a product description such as VNTC Tray Cable 12-2 AWG, the second number refers to the number of current-carrying conductors in the wire I.e. the conductor count.

4) Cable Insulation

A cable or wire is insulated to prevent the wire's current from coming into contact with other conductors. Normally the insulated wire or cable would consist of a non-conductive material that is resistant to electric current.

Typical insulation materials for tray cable include:

• Thermoplastic high heat-resistant nylon water-resistant (THWN)
• Thermoplastic high heat-resistant nylon (THHN)
• Flame retardant ethylene propylene (rubber) (FREP/FR-EPR)
• Ethylene propylene rubber (EPR)
• Cross-linked polyethylene (XLPE/XHHW)
• Cross-linked polyolefin (XLPO)

A VNTC Tray cable uses a THHN insulation while the XPTC tray cable uses an XLP insulation. XPTC's XLP insulation is more durable compared to VNTC.

5) Jacket

Electrical Cable 

A wire or cable jacket is used to offer protection from moisture, flame, chemical, and UV damage. It also protects the cable or wire from damage during and after the installation process. As the cable's outermost layer, a jacket is the first line of mechanical defense for its inner components, providing protection for the shielding and conductors within the cable. Different materials can be used as jackets.

Typical jacket materials include:

• Polyvinyl chloride (PVC) featured in the XLP tray cable
• Chlorinated polyethylene (CPE)
• Thermoplastic rubber/elastomer (TPR/TPE)
• Polyurethane (PUR)
• Polyethylene (PE)

6) Color Code

Color coding is one of the many identification standards used for wires. It is used to establish a standard for use by different manufacturers. Different color codes are used to identify conductors for point-to-point wiring and for circuit diagrams. However, not all wire color codes are the same. They differ based on several factors including but not limited to installation type, location, and voltage. For example, phase 2 of the 120 Volt AC wire is color coded as Red in the United States but Black in Europe.  Some color codes are specified by law but not always as others are based on common practice.

Here is an example of how a wire jacket can communicate its predetermined use to an electrician.

Author: John Olguin

John Olguin is the Southwest Regional Inside Sales at Kris-Tech, a copper wire manufacturing company headquartered in Rome, New York.

If you want to learn more, please visit our website Mineral Insulated Copper Cable.