Mineral Insulated Cable (MICC)

MICC (also known by the trade name Pyrotenax) is constructed with solid copper conductors embedded in highly compressed magnesium oxide (MgO) powder inside a seamless copper tube that serves as both mechanical protection and earth conductor. This construction gives the cable exceptional properties: continuous operating temperature up to 250°C (compared to 70°C for PVC), fire resistance maintaining circuit integrity at over 1,000°C for several hours, immunity to water, oil, and most chemicals, and indefinite service life. These properties make MICC mandatory for fire alarm circuits, emergency lighting, sprinkler pump supplies, smoke extraction fans, and fireman's lifts where circuit integrity during a fire is essential for life safety. The cable requires special termination seals to prevent moisture ingress into the hygroscopic MgO insulation — termination failure is the most common cause of MICC problems. BS 7671 provides specific ampacity tables (Table 4J series) for MICC cables, with ratings significantly higher than polymer-insulated cables of the same conductor size due to the higher operating temperature. The copper sheath can serve as the circuit protective conductor, simplifying installation. Despite its advantages, MICC is more expensive and less flexible than polymer cables, requiring careful route planning and bend radius management.