Understanding MICC Pyro Cable Referencing

We often get asked what is pyro cable? ‘Pyro’ is a reference to the original manufacturer of this copper-sheathed fire survival cable, Pyrotenax. Later becoming a brand of British Insulated Cables, which after merging with Callender’s Cable & Construction Company became British Insulated Callender’s Cables, commonly referred to as BICC. After the closure of the BICC pryo cable plants, Mineral Insulated Cable Company, known as MICC, took over the manufacture and distribution of this leading fire survival cable.

MI cable is made by placing copper rods inside a circular copper tube and filling the intervening spaces with dry magnesium oxide powder. The overall assembly is then pressed between rollers to reduce its diameter (and increase its length). Up to seven conductors are often found in an MI cable, with up to 19 available from some manufacturers.

Since MI cables use no organic material as insulation (except at the ends), they are more resistant to fires than plastic-insulated cables. MI cables are used in critical fire protection applications such as alarm circuits, fire pumps, and smoke control systems. In process industries handling flammable fluids, MI cable is used where small fires would otherwise cause damage to control or power cables. MI cable is also highly resistant to ionizing radiation and so finds applications in instrumentation for nuclear reactors and nuclear physics apparatus.

MI cables may be covered with a plastic sheath, coloured for identification purposes. The plastic sheath also provides additional corrosion protection for the copper sheath.

The metal tube shields the conductors from electromagnetic interference. The metal sheath also physically protects the conductors, most importantly from accidental contact with other energised conductors.

Cable type referencing for pyro fire cable is relatively straightforward;

• Bare cable = CC
• LSF covered = CCM and OR (Orange) or RD (Red) or WH (White) or BK (Black)
• 2= Number of conductors
• L= Light Duty 500v
• H= Heavy Duty 750v
• 1.5= Cross-sectional area of conductors

So a 2 core, 1.5sqmm, 500v, LSF Orange cable would be CCM2L1.5- OR

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Cable Structure

Conductor
Copper –Melting point 1083℃ (copper sheath cable)
Nickel clad copper –Ni melting point 1427℃ (Alloy 825 sheath)

Magnesium oxide insulating layer
High temperature ceramic +2800 ℃
Excellent electrical insulation qualities

Sheath options
Copper -1083℃
Alloy 825 –tested to 1095℃ for 30mins (Alloy 825 melting point 1399 ℃)