Flame resistance electrical cables

The fact that the polymer contains no halogens along with certain unique compounding techniques for flame resistance prompts the selection of ethylene—acryflc as jacketing material on certain transportation/mifltary electrical cables and in floor tiles. 

These materials are developed from the polyetherimides introduced by General Electric (see also Section 18.14.2). At the time of writing one grade, Ultem Siltem STM 1500, is being offered. It is of particular interest as a material for wire and cable insulation, as it not only has excellent flame resistance coupled with low smoke generation but also avoids possible toxic and corrosion hazards of halogenated polymers. This can be of importance where there are possible escape problems in the event of a fire, such as in tunnels, aircraft and marine (particularly submarine) vessels. 

Examples of fluoroplastics include polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP), ethylene—chlorotrifluoroethylene (ECTFE), ethylene—tetrafluoroethylene (ETFE), poly(vinylidene fluoride) (PVDF), etc (see Fluorine compounds, organic). These polymers have outstanding electrical properties, such as low power loss and dielectric constant, coupled with very good flame resistance and low smoke emission during fire. Therefore, in spite of their relatively high price, they are used extensively in telecommunication wires, especially for production of plenum cables. Plenum areas provide a convenient, economical way to run electrical wires and cables and to interconnect them throughout nonresidential buildings (14). Development of special flame-retardant low smoke compounds, some based on PVC, have provided lower cost competition to the fluoroplastics for indoors application such as plenum cable, Riser Cables, etc. 

ASTM D 6113 Standard Test Method for Using a Cone Calorimeter to Determine Fire-Test-Response Characteristics of Insulating Materials Contained in Electrical or Optical Fiber Cables ASTM D 6194 Standard Test Method for Glow Wire Ignition of Materials ASTM D 6413 Standard Test Method for Flame Resistance of Textiles (Vertical Test)... 

Electrical Communications Low dielectric constant High volume/surface resistivity High dielectric breakdown voltage Flame resistance, thermal stability Wire and cable insulation, connectors... 

A flame resistant grade of PP/EPDM elastomeric is used for extmsion-coating electrical cables because it contains only 5.5 percent acid-gas materials, compared to PVC that contains 25 percent. Large concentrations of acid-gas can corrode the surface of sensitive electronic equipment if exposed to fire. 

SEES rubbers find applications for a wide variety of general-purpose rubber items as well as in automotive, sporting goods, and other products. Many applications are found in the electrical industry for such items as flexible cords, welding and booster cables, flame-resistant appliance wiring materials, and automotive primary wire insulation. 

All pipelines, valves (including shut off and non-return valves) fittings shall be as per international standards (pressure tested and corrosion resistant). These shall be tested regularly and faulty parts replaced by new ones immediately. Layout of the gas pipelines must avoid proximity to electrical cables, furnaces, and process ducts operating at high temperatures, areas where naked flames could be present. 

Until very recently, almost all PVC cables were stabilised with lead salts. These gave good thermal stability and electrical resistance, with low water absorption. When the cable was required to have better flame resistance than inherent in PVC, a small part of the calcium carbonate filler was replaced by antimony trioxide. All such cables perform well and have done for many years. Now, however, the need to focus on ecotoxicity has caused the lead salts to be replaced by a non-heavy metal system, usually a calcium-zinc complex. Likewise, the role of antimony is being questioned and formulators have come up with other solutions. 

Natural rubber/chlorosulfonated polyethylene rubber blends also exhibited immiscibility. Chlorosulfonated polyethylene rubber is the synthetic rubber used for applications in electric cables, hoses for liquid chemicals, waterproof cloths, floor tiles, and oil-resistant seals. It is chosen to blend with natural rubber to improve the resistance of natural rubber to ozone, oil, heat, flame and non-polar chemicals. This is due to the effect of the polarity of the chlorine groups in the chlorosulfonated polyethylene rubber. The tensile strength, elongation at break, and tear strength of these blends decreased with the increasing chlorosulfonated polyethylene rubber contents. In addition, the compatible natural rubber/chlorosulfonated polyethylene rubber blends were improved by adding the epoxidized natural rubber (Epoxyprene 25) as a... 

One of the very first plasticizers proposed for PVC was the phosphate ester tricresyl phosphate. This plasticizer was later used for its flame-resistant properties in the first commercial PVC electrical wire insulation materials. Today the majority of the phosphate esters used as plasticizers are the alkyl diaryl phosphates, which are prepared with mixtures of various phenols and alcohols and often used in combination with GP plasticizers such as DINP, DIDP, or DPHP. Phosphate esters provide significant improvement in flame retarding properties and for some products, reduced smoke generation. This property helps enable flexible PVC materials to be used in plenum cables, data and communication cables, and electronics. Phosphates such as isodecyl diphenyl phosphate can also be used in transportation fabrics and wall coverings where some level of flame retardant properties is required. 

Electrical Communications Low Dielectric Constant High Volume/Surface Resistivity High Dielectric Breakdown Voltage Flame Resistance, Thermal Stability Wire and Cable Insulation, Connectors... 

Chloroprene Neoprene (CR) 100-800 50 to 105 (60 to 225) Excellent ozone, heat, and weathering resistance good oil resistance excellent flame resistance not as good in electrical applications as natural rubber Wire and cable chemical tank linings belts, hoses, seals, and gaskets... 

This filler is useful when flame resistant compounds, with low smoke emission characteristics are being produced. Because compounds loaded with alumina retain good insulation properties (from the electrical point of view) hydrated alumina has been used successfully in the production of electric cable insulation compounds where good flame retardance is required. 

Commonly used materials for cable insulation are poly(vinyl chloride) (PVC) compounds, polyamides, polyethylenes, polypropylenes, polyurethanes, and fluoropolymers. PVC compounds possess high dielectric and mechanical strength, flexibiUty, and resistance to flame, water, and abrasion. Polyethylene and polypropylene are used for high speed appHcations that require a low dielectric constant and low loss tangent. At low temperatures, these materials are stiff but bendable without breaking. They are also resistant to moisture, chemical attack, heat, and abrasion. Table 14 gives the mechanical and electrical properties of materials used for cable insulation. 

Tests for Fire Resistance of Roof Covering Materials, 1983. (similar to ASTM E 108) Tests for Flame Propagation and Smoke Density Values for Electrical and Optical Fiber Cables in Spaces Transporting Environmental Air, 1991. 

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