MICC (Mineral Insulated Copper Clad Cable)

Overview

MICC (Mineral Insulated Copper Clad) cable is a fire-resistant cable consisting of:

• Solid copper conductors
• Compressed magnesium oxide (MgO) insulation
• A seamless copper outer sheath

It provides exceptional fire resistance, maintaining circuit integrity under extreme temperatures where conventional polymer cables would fail.

MICC is often referred to as:

• Pyro cable
• Mineral insulated cable

Construction

Unlike polymer-based cables, MICC contains no combustible materials, making it inherently fireproof.

Key Characteristics

• Extremely high temperature resistance
• Maintains circuit integrity during fire conditions
• Mechanically robust (but not flexible)
• Resistant to UV, oils, and chemicals (to a degree)
• Fully inorganic insulation system

Applications

MICC is typically used in critical life safety and high-risk environments, including:

• Fire alarm circuits (historically and in critical areas)
• Firefighting systems
• Emergency lighting supplies
• Smoke control systems
• Industrial and hazardous environments

It is often specified where enhanced fire resistance is required under BS 5839.

Advantages

• Excellent fire survival performance
• No smoke or toxic gas emission
• Long lifespan when correctly installed
• Resistant to environmental degradation (when intact)

Limitations

• Difficult to install compared to modern cables
• Requires specialist termination methods
• Poor flexibility (tight bending can cause damage)
• Higher cost
• Susceptible to moisture-related issues if compromised

Installation Considerations

Bending Radius

• MICC has a limited bending radius

• Over-bending can:

  • crack insulation internally
  • weaken the copper sheath

Support and Fixings

• Must be supported using metal fixings
• Heavy compared to standard cables
• Care required to avoid mechanical stress points

Routing

• Avoid sharp edges or crushing forces
• Protect terminations from mechanical damage
• Maintain continuity of the copper sheath where required

Termination

Termination is one of the most critical aspects of MICC installation.

Typical components:

• Glands
• Pots
• Seals
• Sleeving

The termination must:

• prevent moisture ingress
• maintain insulation integrity
• ensure correct earthing of the sheath

Poor termination is one of the most common failure points.

Common Issues (Field Experience)

1. Moisture Ingress (Major Issue)

Magnesium oxide insulation is hygroscopic (absorbs moisture).

If the sheath or termination is compromised:

• moisture enters the cable
• insulation resistance drops
• cable performance degrades

Symptoms:

• Low insulation resistance readings
• Intermittent faults
• Earth leakage

Common causes:

• Poorly sealed terminations
• Damaged sheath
• Long-term exposure to damp environments

2. Copper Sheath Degradation

The outer copper sheath can:

• oxidise (green patina)
• become brittle over time
• crack under environmental stress

This is especially common:

• outdoors
• in coastal or industrial environments

Cracked sheath = direct path for moisture ingress.

3. Installation Damage

Because MICC is rigid:

• excessive bending can fracture insulation internally
• impacts can deform the copper sheath
• crushing can compromise the internal structure

Damage is often not immediately visible.

4. Termination Failures

Improper termination leads to:

• moisture ingress
• poor insulation
• unreliable connections

Common mistakes:

• incorrect potting
• missing seals
• poorly fitted glands

5. High Installation Skill Requirement

MICC requires:

• trained installers
• correct tools
• attention to detail

Poor workmanship = long-term reliability issues.

Testing and Maintenance

Insulation Resistance Testing

• Critical for detecting moisture ingress
• Low readings often indicate contamination of MgO insulation

Visual Inspection

Check for:

• cracked or damaged sheath
• corrosion
• compromised terminations

Ongoing Monitoring

Older MICC installations may:

• degrade slowly over time
• require periodic reassessment

Comparison with Modern Alternatives

Modern cables are typically preferred unless:

• extreme fire resistance is required
• specified by design
• legacy systems are being maintained

Practical Guidance

• Avoid unnecessary use unless required by design
• Ensure high-quality terminations
• Protect all exposed ends during installation
• Always test insulation resistance after installation
• Be cautious when modifying or extending existing MICC circuits

Summary

MICC cable provides exceptional fire performance, but comes with:

• high installation complexity
• sensitivity to moisture if damaged
• long-term degradation risks in harsh environments

When installed correctly, it is highly reliable, however, poor workmanship or environmental exposure can significantly reduce its effectiveness.