Copper-coated copper wires are various electrical wires made of copper conductors in copper sheath, isolated by an inorganic magnesium oxide powder. The name is often abbreviated by MICC or MI cable, and colloquially known as pyro (since the original manufacturer and vendor for this product in the UK is a company called Pyrotenax). A similar product coated with a metal other than copper is called mineral insulated metal sheathed cable (MIMS).
Video Mineral-insulated copper-clad cable
Construction
The MI cable is made by placing the copper rod inside the circular copper tube and filling the intervening chamber with dry magnesium oxide powder. The entire assembly is then pressed between rollers to reduce its diameter (and increase its length). Up to seven conductors are often found in MI cables, with up to 19 available from multiple manufacturers.
Because MI cables do not use organic materials as insulation (except at the ends), they are more resistant to fire than plastic-coated wires. MI cables are used in critical fire protection applications such as alarm circuits, fire pumps, and smoke control systems. In the flammable liquid handling process industry, MI cables are used if a small fire will cause damage to the control or power cord. The MI cable is also highly resistant to ionizing radiation and thus finds applications in instrumentation for nuclear reactors and nuclear physics apparatus.
The MI cable can be covered with a plastic cover, colored for identification purposes. Plastic sheath also provides additional corrosion protection for copper sheath.
The metal tube protects the conductors from electromagnetic interference. The metal sheath also physically protects the conductor, most importantly from accidental contact with other energetic conductors.
Maps Mineral-insulated copper-clad cable
History
The first patent for MI cable was issued to the Swiss inventor, Arnold Francois Borel in 1896. Initially the insulating mineral is described in patent applications as crushed glass, dangerous stones, or asbestos, in powder form. Much of the development is done by the French company Socià © Ã… © Alsacienne de Construction MÃÆ'  © canique. Commercial production began in 1932 and many mineral insulated cables were used on ships such as Normandie and oil tankers, and in critical applications such as the Louvre museum. In 1937 a British firm Pyrotenax , after purchasing a patent on a product from a French company, began production. During the Second World War many company products were used in military equipment.
Around 1947, the British Cable Maker Association investigated the option of making mineral-insulated cables that would compete with Pyrotenax products. Manufacturers of products "Bicalmin" and "Glomin" eventually joined the company Pyrotenax.
The Pyrotenax Company introduced the aluminum sheathed product in 1964. MI cables are now produced in several countries. Pyrotenax is now a brand name under nVent (formerly known as Pentair Thermal Management).
Goal and use
The MI cable is used for power circuits and controls of critical equipment, such as the following example:
- Nuclear reactor
- Exposure to hazardous gas
- Air air pressure system for ladders to allow for building exits during fires
- Hospital operating room
- Fire alarm system
- Emergency systems
- Emergency lighting system
- Temperature gauge; RTD and Thermocouple.
- Critical process valves in the petrochemical industry
- Public buildings such as cinemas, cinemas, hotels
- Transport hub (railway station, airport, etc.)
- Power supply cables in residential apartment blocks
- Tunnels and mines
- Electrical equipment in hazardous areas where combustible gas may be present eg. refineries, gas stations
- Areas where corrosive chemicals may be present eg. factory
- Build factory space
- Hot area eg. power plants, metal casting, and near or even inside an industrial furnace, kiln and oven
The MI cable meets passive fire protection called integrity circuits, which are intended to provide the operability of critical electrical circuits during a fire. This is subject to a rigorous list and use of approval and compliance
Cable heater
A similarly emerging product is a mineral-insulated trace heater cable, in which conductors are made of high-resistance alloys. Heating cables are used to protect pipes from freezing, or to maintain the temperature of piping and ship processes. The heating cable of MI resistance may not be repaired if it is damaged. Most electric stoves and heating elements are built in the same way.
General specifications
Benefits
The metallic sheath and filling of a heavy MI cable make it mechanically strong and resistant to impact; MI cables can be hit repeatedly with a hammer and still provide adequate insulation resistance for the circuit. The copper sheath is waterproof and resistant to ultraviolet light and many corrosive elements. MI cable approved by the electrical code for use in areas with concentrations of harmful flammable gases in air; The MI cable will not allow the explosion spreading inside the copper tube, and the cable is unlikely to start the explosion even during a circuit breakdown condition. The metal sheath will not contribute fuel or harmful combustion products to the fire, and can not spread the flame along the cable tray or inside the building. This cable is inherently switched on without additional coatings, and will survive a designated fire test that represents actual fire conditions longer than the cover structure.
When used in a rented area, carrying electricity supplied and billed to the landlord, for example for a communal extraction system or an antenna amplifier, it provides a supply cable that can not be easily tapped for free energy.
Although made of solid copper elements, cable assemblies are still flexible due to the flexibility of copper. The cable can be bent to follow the shape of the building or bend around the obstacles, allowing for a neat appearance when exposed.
Because inorganic insulation is not degraded with warming (moderate), completed cable assemblies can be allowed to rise to higher temperatures than plastic-coated wires; the temperature rise limit may be due to the possibility of sheath contact with a person or structure. It also allows smaller cross-sectional cables to be used in certain applications.
Due to oxidation, dark copper cladding with age and MICC is therefore often used in historic buildings such as castles where it blends with stones. However, where MICC cables with bare copper sheaths are installed in wet locations, especially where limestone has been used, water and limestone combine to create electrolytic action with bare copper. Similarly, electrolytic action may also be caused by the installation of bare MICC cables in new oak trees. The reaction causes the copper to be eaten, making holes on the sides of the wires and letting the water, causing a short-circuit between life, neutral and earth. The appearance of green verdigris on a bare copper shell could be a sign of this has happened.
Disadvantages
- Termination point: While the length of the MI cable is very difficult, at some point, any cable braking ends on the connection or inside the electrical equipment. This termination is susceptible to fire, humidity, or mechanical impact.
- Vibration: MICC is not suitable for use where it will experience vibration or stretching, eg connection to heavy or moving machine. Vibration will break the cladding and core, leading to failure.
- Labor Cost: During the installation of the cable the MI should not be bent repeatedly as this will cause work hardening and cracks in the cladding and core. A minimum bend radius should be observed and cables must be supported periodically. The isolation of magnesium oxide is hygroscopic so that the MICC cable must be protected from moisture until it has been discontinued. Termination requires stripping back the copper cladding and fitting of the compression gland. Individual conductors are insulated with plastic sleeves. Sealing tape, insulating putty or epoxy resin is then poured into the compression gland fittings to provide a watertight seal. If disconnection is wrong due to workmanship or damage then magnesium oxide will absorb moisture and lose its insulating properties. Depending on the size and number of conductors, a single termination can take between 1 and 2 hours of work (an electrical expert must be able to create a stop in 10 to 15 minutes on up to 4 smaller size cores). The three-conductor MI cable (size No. 10 AWG - about 5 mm square) takes about 65% longer than PVC coated steel wiring with the same conductor size. Installing MICC is an expensive task. Certain PTFE, silicon or other polymer-insulated cables have been replaced in applications that require similar properties in terms of fire spread, which uses less labor to terminate. MICC is still used in applications that are very suitable for property combinations.
- Voltage rating: The MI cable is only built with ratings up to 1000 volts.
- Moisture absorption: Isolation of magnesium oxide has a high affinity for moisture. Humidity inserted into the cable can cause electrical leakage from the internal conductor to the metal housing. The moisture absorbed at the end of the cable can be turned off by heating the cable.
- Corrosion: The copper sheath material is resistant to most chemicals but can be severely damaged by ammonia and urine carrier compounds. A pinhole in the copper jacket will allow the moisture to enter into insulation, and eventually the circuit failure. PVC over jackets or sheaths of other metals may be required where such chemical damage is expected. When the MI cable is embedded in the concrete as a snow smelter, it will be physically damaged by a concrete worker working concrete into the pour. If 3-5mil coating is damaged, the pin hole in the copper jacket develops causing premature failure of the snow smelter system.
- Repair: If the MI cable jacket has been damaged, magnesium oxide will obscure water vapor into the wire and will lose its insulating properties causing shorts to the copper cladding, and from there to the earth. It is often necessary to remove 0.5 to 2 meters (1.6 to 6.6Ã, ft) from the MI cable and splice in the new section to complete the repair. Depending on the size and number of conductors, a termination can take between one and two working hours.
Alternative
Integrity circuits for conventional plastics-insulated cables require additional steps to obtain a fireproof rating or to decrease flammability and smoke contribution to an acceptable minimum level for certain types of construction. Flexible spray coating or wrapping covers plastic insulation to protect it from fire and reduce its ability to spread the flame. However, since these coatings reduce heat dissipation from cables, they often need to be judged less current after application of fireproof coatings. This is called a decrease in current capacity. This can be tested through the use of the IEEE 848 Standard Procedure for Determination of Ampacity Derating Fire-Protected Cables.
See also
- Use and list compliance and approval
- Passive fire protection
- Integrity circuit
- Fireproofing
- Cable tray
- Copper wires and cables
References
External links
- https://web.archive.org/web/20150508095130/http://www.wrexhammineralcables.com/Mineral wire Wrexham, manufacturer of MICC cables in the UK
- https://www.micable.com/MI Cable Company, US manufacturer of MI Cable assemblies in the United States
Source of the article : Wikipedia
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