Introduction

Mineral Insulated Cable (MICC or MI cable)​ is a specialized type of cable in which copper conductor cores are enclosed within a seamless copper sheath, and magnesium oxide (MgO) powder​ serves as the inorganic insulating material separating the conductors from the sheath. An outer protective jacket can be added if required. A closely related variant uses a metal sheath other than copper to encase the cores and insulation, commonly referred to as Mineral Insulated Metal Sheathed Cable (MIMS Cable).

Development & Current Status

The history of MI cable dates back to 1896 in Switzerland. It was introduced to France in 1934​ and began to flourish in the UK and US by 1936. Its exceptional fire‑resistant properties led to widespread adoption. Even today, China’s testing standard for mineral cables—BS 6387—is based on the original British standard.

Initially, only rigid​ MI cables were available. After entering the Chinese market, high production costs limited both manufacturers and users. The turning point came in 2015​ with the implementation of GB/T 50016, which mandated the compulsory use of MI cables for fire‑fighting circuits. Since then, the domestic MI cable industry has experienced rapid growth.

Classification by Structure and Standard

National Standard Rigid Cable Models (6 total)

• Light duty 500V:​ BTTQ, BTTVQ, WD‑BTTYQ

• Heavy duty 750V:​ BTTZ, BTTVZ, WD‑BTTYZ

National Standard Flexible Cable Models

• RTTZ, RTTYZ, RTTV1Z​ — Voltage ratings: 0.6/1 kV or 450/750 V

Enterprise Standard Flexible Cable Models (examples)

• BTWTZ, GAN‑BTGYZ, BTLY, NG‑A, and over ten additional proprietary designations.

Note:​ Article 2.0.1 of JGJ 232‑2011 Technical Specification for Installation of Mineral Insulated Cablesdefines mineral insulated cables as those using annealed copper conductors, compacted magnesium oxide insulation, and annealed copper or copper alloy sheaths.

Testing Standards in China

Key references include:

• BS 6387​ — Test method for fire resistance of cables under flame conditions(C – combustion, W – water spray, Z – mechanical impact)

• GB/T 19216.21​ — Circuit integrity test for cables or optical cables under flame conditions

• GB/T 13033‑2007​ — Mineral insulated cables and terminations rated up to 750 V

Categories & Key Differences

All flexible mineral cables except​ the national standard rigid types are produced to enterprise standards. Here’s how they compare:

Design tip:​ Smaller allowable bending radii make installation easier. Choose the product that fits the actual site conditions and cable tray constraints.

Advantages of Mineral Insulated Cables

Because every component is inorganic, these cables offer benefits unmatched by conventional cables:

1. Fire Resistance​ — Copper and MgO will not burn or propagate fire. Operation can continue even near flame. Copper sheath melts at 1083 °C.

2. High Operating Temperature​ — Continuous operating temperature up to 250 °C; short‑term operation possible near copper melting point.

3. Long Service Life​ — Inorganic materials ensure stability and longevity; no aging.

4. Explosion Proof​ — Densely compacted insulation prevents gases, vapors, and flames from passing through to connected equipment.

5. Small Outer Diameter​ — More compact than equivalently rated cables.

6. Waterproof​ — Seamless metal sheath allows continued operation even when fully submerged.

7. High Mechanical Strength​ — Withstands severe mechanical damage without compromising electrical performance.

8. High Current Carrying Capacity​ — Superior thermal conductivity of mineral insulation allows higher ampacity; also tolerates significant overload.

9. High Short‑Circuit Rating​ — Far exceeds that of conventional cables at the same temperature.

10. Grounding Capability​ — The copper sheath itself acts as an excellent grounding conductor with very low resistance.

11. Corrosion Resistance​ — Copper sheath resists corrosion in most environments; PVC outer jacket can be added for harsh chemical conditions.

Product Characteristics

1. Fire Resistance

Composed entirely of metal copper and MgO powder, the cable does not cause or support combustion. With copper melting at 1083 °C and MgO above 1000 °C, it can maintain power supply during severe fires. Passes BS 6387 C, W, Z tests.

2. High Ampacity & Waterproof

Actual service temperature reaches 250 °C (IEC 60702 specifies 105 °C for safety). Higher thermal conductivity means larger current capacity—for conductors ≥16 mm², cross‑section can be reduced by one size; in inaccessible locations, by two sizes.

3. Explosion Proof & Corrosion Resistant

Metal sheath blocks flammable gases and flames. Copper sheath provides inherent corrosion resistance; PVC jacket adds protection in aggressive environments.

4. Mechanical Damage Resistance, Long Life, Halogen‑Free

Bending, crushing, or twisting won’t cause short circuits. Service life spans centuries at normal temperatures (oxidation rate data shows >250 years). Zero halogen, zero toxic gas​ emission even at 1000 °C.

5. Overload Capacity & Copper Sheath as Ground

Copper melting point and MgO withstand massive overload—up to 10× normal current. Copper sheath serves as grounding conductor, eliminating need for separate earth wire.

6. Applications

Suitable for ≤1000 V​ circuits in:

• General lighting & emergency lighting

• Emergency broadcast systems

• Elevators & lift equipment

• Fire alarm control

• Computer room controls

• Fire fighting electrical circuits

• Generator room power transmission

• Uninterruptible power lines

• Dual‑power control

• Public area lighting

• Main/sub distribution systems

• Heritage site lighting

• High‑temperature environments

• Oil pump circuits

• Potentially explosive areas

Application Fields

Mineral insulated cables are widely deployed in:

Conclusion

Mineral insulated cables represent the pinnacle of fire‑safe wiring technology. Their all‑inorganic construction delivers unmatched fire resistance, longevity, and reliability​ across the most demanding applications. As building codes tighten and safety expectations rise, MI cables will continue to play a vital role in protecting lives and critical infrastructure worldwide.