Mineral Insulated Copper Clad (MICC) cable is the ultimate fire-performance cable for UK electrical installations. This guide covers its unique properties, fire survival capability, correct termination and sealing, testing procedures, and the BS EN 60702 standard — essential knowledge for fire alarm, emergency lighting, and critical circuit installations.
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Written and reviewed by Andrew Moore, founder of Elec-Mate, against BS 7671:2018+A4:2026, IET Guidance Note 3 and the IET On-Site Guide.
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Mineral Insulated Copper Clad (MICC) cable — also known by the trade name Pyrotenax — is a specialised cable type consisting of copper conductors insulated with compressed magnesium oxide powder, enclosed within a seamless copper outer sheath. The entire cable is a solid, continuous metallic structure with no organic materials that could burn or decompose.
The construction is remarkably simple: one or more solid copper conductors are surrounded by densely packed magnesium oxide (MgO) powder, which provides electrical insulation. The assembly is enclosed in a seamless drawn copper tube that serves as both the mechanical protection and the circuit protective conductor. The cable is manufactured by drawing the assembly through a series of dies, compressing the MgO powder and reducing the overall diameter to the required size.
MICC cable is available in single-conductor (light duty), 2-core, 3-core, 4-core, 7-core, 12-core, and 19-core configurations, in conductor sizes from 1.0 mm squared to 240 mm squared. For fire alarm and emergency lighting installations, the most common sizes are 1.5 mm squared 2-core and 1.5 mm squared 3-core. For power circuits requiring fire survival, larger sizes are used.
The cable is manufactured to BS EN 60702-1 (cable specification) and BS EN 60702-2 (terminations), which replaced the older BS 6207. It is classified as fire-resistant cable but goes far beyond the minimum requirements of standard fire-resistant cables — MICC can operate continuously at 250 degrees Celsius and survive short-term exposure to over 1,000 degrees Celsius.
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MICC cable has several unique properties that make it the premium choice for critical electrical circuits. Understanding these properties is essential for correct specification, installation, and maintenance.
MICC cable is specified where circuit integrity during fire is essential — the cable must continue to supply power to critical safety systems even while the building is on fire. The relevant standards and regulations define specific applications:
BS 5839-1 (fire detection and alarm systems for buildings) requires that cables serving fire alarm systems in certain categories maintain circuit integrity during fire. MICC cable meets the enhanced fire resistance requirements and is the traditional choice for fire alarm mains wiring in commercial and industrial premises. For domestic fire alarm installations to BS 5839-6, MICC or standard fire-resistant cable may be used depending on the system category.
BS 5266 requires fire-resistant cabling for centrally supplied emergency lighting systems. MICC cable ensures that the emergency lighting supply survives the fire, providing illumination for evacuation routes even in severe fire conditions.
Smoke ventilation (smoke extract) systems must operate during a fire to clear smoke from escape routes. The power supply cables to smoke extract fans, damper actuators, and control panels must maintain circuit integrity during fire, making MICC cable the standard specification.
Fire-fighting lifts must remain operational during a fire to allow firefighter access to upper floors. Sprinkler pump motors must continue to run to maintain water supply. Both applications require fire-surviving power cables, and MICC cable is the standard choice for these critical supplies.
MICC cable is also used in harsh industrial environments — petrochemical plants, steelworks, power stations — where its resistance to heat, fire, moisture, oil, and mechanical damage makes it superior to any organic-insulated cable.
Correct termination of MICC cable is the most critical aspect of the installation. The magnesium oxide insulation must be sealed against moisture ingress at every termination point — if the seal fails, moisture enters the MgO, insulation resistance drops, and the cable will fail insulation resistance testing and may trip RCD protection.
There are two main termination methods for MICC cable:
The traditional pot seal consists of a brass pot (disc) that is soldered or crimped onto the stripped copper sheath. The pot is filled with a sealing compound (historically a two-part epoxy, now often silicone-based) that completely encapsulates the exposed MgO insulation and the conductor tails. The conductor tails (PVC-insulated extensions) emerge from the seal for connection to the accessory or equipment.
Pot seals require skill and practice to install correctly. The key steps are: clean the copper sheath thoroughly, fit the brass pot squarely onto the sheath, solder or crimp the pot, attach the conductor tails (by crimping or screw connection), fill the pot with sealant, and fit the PVC shroud.
Modern compression glands (screw-on type) simplify MICC termination. The gland body screws onto the stripped copper sheath, and a compression olive seals the sheath. An internal insulating disc separates the conductors and provides the moisture seal. Pre-insulated conductor tails are attached using push-fit or screw terminals within the gland.
Compression glands are faster to install than pot seals and are less dependent on the installer's soldering skill. They are now the preferred termination method for most new installations.
Elec-Mate's fire alarm certificate forms include specific fields for cable type (MICC, FP200), insulation resistance results…
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Start free trialMICC cable provides the highest level of fire performance of any cable type available. Its fire survival characteristics are governed by BS EN 60702 and tested to the fire resistance classification standards that define how cables behave under fire conditions.
The key fire performance characteristics of MICC cable are:
The relevant standard for MICC cable is BS EN 60702-1 (specification for cables) and BS EN 60702-2 (specification for terminations). These replaced the older BS 6207 standard. Fire resistance testing is carried out to BS EN 50200 (circuit integrity under fire), with cables meeting the PH120 classification (120 minutes circuit integrity at 830 degrees Celsius or above).
Testing MICC cable installations follows the standard BS 7671 testing sequence, but with particular attention to insulation resistance. The insulation resistance test is the primary indicator of whether the cable seals are intact and the MgO insulation is dry.
During periodic inspection, pay particular attention to the insulation resistance of MICC circuits. A gradual decline in insulation resistance over successive inspections indicates progressive moisture ingress, usually at a deteriorating seal. This should be recorded as a C3 observation (improvement recommended) or C2 (potentially dangerous) if the readings drop below acceptable levels.
Elec-Mate's certificate forms capture insulation resistance readings with trend analysis — compare current readings against previous inspection results…
Try it free for 7 daysMICC cable and FP200 (fire performance) cable are both used for fire-critical circuits, but they are fundamentally different products with different performance characteristics, installation requirements, and costs.
For most fire alarm and emergency lighting installations in standard commercial and domestic buildings, FP200 or equivalent fire-resistant cable provides adequate fire performance and is significantly easier and cheaper to install than MICC. MICC cable is reserved for the most demanding applications — large commercial buildings, high-rise residential, hospitals, critical infrastructure — where the absolute maximum fire performance is required and the installation budget supports the additional cost.
The FP200 cable guide provides detailed specification and installation guidance for fire performance cables.
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