Mineral-insulated copper-clad cable
The name is often abbreviated to MICC or MI cable, and colloquially known as pyro (because the original manufacturer and vendor for this product in the UK was a company called Pyrotenax).
Initially the insulating mineral was described in the patent application as pulverised glass, silicious stones, or asbestos, in powdered form.
[1] Commercial production began in 1932 and much mineral-insulated cable was used on ships such as the Normandie and oil tankers, and in such critical applications as the Louvre museum.
It is subject to strict listing and approval use and compliance A similar-appearing product is mineral-insulated trace heating cable, in which the conductors are made of a high-resistance alloy.
MI cable is approved for use in areas with hazardous concentrations of flammable substances, being unlikely to initiate an explosion even during circuit fault conditions.
The cable meets and exceeds BS 5839-1, making it fire-rated surpassing 950°c for over three hours with simultaneous mechanical stress and water spray as well without failure.
MI cable is primarily used for high-temperature environments or safety-critical signal and power systems; however, it can additionally be used within a tenanted area, carrying electricity supplied and billed to the landlord.
For example, for a communal extract system or antenna booster, it provides a supply cable that cannot easily be 'tapped' into to obtain free energy.
Since the inorganic insulation does not degrade with (moderate) heating, the finished cable assembly can be allowed to rise to higher temperatures than plastic-insulated cables; the limits to temperature rise may be only due to possible contact of the sheath with people or structures or the physical melting point of copper.
The copper sheath material is typically resistant to most chemicals but can be severely damaged by ammonia-bearing compounds and urine.
If the coating is damaged, pinholes in the copper jacket may develop, causing premature failure of the system.
During installation MI cable must not be bent repeatedly, as this will cause work hardening and cracks in the cladding and cores.
If a termination is faulty due to workmanship or damage, then the magnesium oxide will absorb moisture and lose its insulating properties.
[6] Circuit integrity for conventional plastic-insulated cables requires additional measures to obtain a fire-resistance rating or to lower the flammability and smoke contributions to a minimum degree acceptable for certain types of construction.
Sprayed-on coatings or flexible wraps cover the plastic insulation to protect it from flame and reduce its flame-spreading ability.
