Cable, insulation resistance

Fig. 55. Principle of a guarded signal wire in case of a source resistance of the same magnitude as the cable insulation resistance...

Nylon A class of synthetic fibres and plastics, polyamides. Manufactured by condensation polymerization of ct, oj-aminomonocarboxylic acids or of aliphatic diamines with aliphatic dicarboxylic acids. Also rormed specifically, e.g. from caprolactam. The different Nylons are identified by reference to the carbon numbers of the diacid and diamine (e.g. Nylon 66 is from hexamethylene diamine and adipic acid). Thermoplastic materials with high m.p., insolubility, toughness, impact resistance, low friction. Used in monofilaments, textiles, cables, insulation and in packing materials. U.S. production 1983 11 megatonnes. 

Properties desired in cable insulation and flexible circuit substrate materials include mechanical flexibiUty, fatigue endurance, and resistance to chemicals, water absorption, and abrasion. Both thermoplasts and thermosets are used as cable-insulating materials. Thermoplastic materials possess excellent electrical characteristics and are available at relatively low cost. 

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. 

Anode supports, cable insulators and the coating on the object to be protected can be destroyed by anodic evolution of chlorine (see Section 7.1), Only chorine-resistant materials should be used. Anodes on retaining walls or between pile foundations can be installed in perforated or fabricated plastic tubes (half-shells) (see Fig. 16-8). They must naturally be provided with very many holes to avoid uneven removal of anode material. Filter tubes of a chlorine-resistant special material or... 

Interest in EVA as a cable-insulating material has arisen because of the good resistance to stress cracking and because the polymer may be more easily cross-linked (see Table 11.12). 

This copolymer has proved particularly suitable for wire and cable insulation, with many grades being rated at 155°C for 20 000 h continuous exposure. It is extensively used in electrical systems for aircraft, underground railways, computers, telecommunications installations and heating circuits. Because of its toughness combined with its heat and chemical resistance it also finds use for lining pumps and valves and other equipment for the chemical industry and for laboratory ware. 

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. 

Butyl ruhher vulcanizates have tensile strengths up to 2,000 psi, and are characterized hy low permeahility to air and a high resistance to many chemicals and to oxidation. These properties make it a suitable rubber for the production of tire inner tubes and inner liners of tubeless tires. The major use of butyl rubber is for inner tubes. Other uses include wire and cable insulation, steam hoses, mechanical goods, and adhesives. Chlorinated butyl is a low molecular weight polymer used as an adhesive and a sealant. 

Wiring checks, including insulation resistance and any pilot cables. 

Flexible RP These materials are used with elastomeric materials providing special engineered products such as conveyor belts, mechanical belts, high temperature or chemical resistant suits, wire and cable insulation, and architectural designed shapes. 

Fig. 3.34 LDA of the microarray signal patterns obtained in practical KAMINA tests to detect gaseous precursors of smoldering fires through overheated cable insulation. Prior to the LDA the measured resistances of the sensor segments were normalized to the median of all sensor segments and the number of variables was reduced by a Principal Component Analysis (PCA) to cutback the noise. Clear distinction is achieved between clean air...

Electrical conductors are normally insulated for protection and avoidance of electrical shorting. Typical insulating materials are plastics that can readily bum with toxic vapors. The NEC specifies certain fire resistant rating to electrical cables to lessen the possibility of cable insulation ignitability and fire spread. 

Another example is the influence of the electrical resistance of PVC cable insulation. This is caused not by the organic pigment itself but by ethoxylated surfactants, which are added as auxiliaries in the manufacture of these pigments, especially azo pigments. Contrary to a repeatedly expressed view, a possible electrolyte content, which laked azo pigments for example can have, has no effect on the dielectric properties of PVC [34]. Some pigment manufacturers offer special product ranges with verified dielectric properties for this purpose. 

P. O.13 sample reaches only step 4. Transparent P.O.34 colorations in rigid PVC are even more resistant to light. Pigment concentrations of less than ca. 0.1% are likewise unsuitable, due to the necessity to avoid blooming. The pigment is also used in vinyl floor coverings and in cable insulations. 

P.R.41 is also known as pyrazolone red. It has lost most of its commercial importance in recent years. P.R.41 production is now limited to the USA, where it is mostly employed to lend color to rubber. To a lesser extent, P.R.41 is found in PVC excellent dielectrical properties make it a suitable candidate for PVC cable insulations. The pigment provides a medium to bluish red of limited brilliance, it is much bluer than P.R.38. P.R.41 is somewhat less fast than P.R.38, which is also true for its stability to a variety of organic solvents. However, it parallels P.R.38 in its alkali and acid resistance. P.R.41 is very lightfast in rubber 1% pigment concentrations equal step 6-7 on the Blue Scale, which meets practically any require-... 

Combustion products can affect sensitive electronic equipment. For example, hydrogen chloride (HCI) is formed by the combustion of PVC cables. Corrosion due to combusted PVC cable can be a substantial problem. This may result in increased contact resistance of electronic components. Condensed acids may result in the formation of electrolytic cells on surfaces. Certain wire and cable insulation, particularly silicone rubber, can be degraded on exposure to HCI. A methodology for classifying contamination levels and ease of restoration is presented in the SFPE Handbook... 

Wire and cable insulation, hose footwear, mechanical automotive products. Good resistance to oil and fire, good weatherability Seals, gaskets, wire, and cable insulation. Good resistance to chemicals Cable insulation, window strips. Outstanding... 

Terpolymers in which the acrylate monomer is the major component are useful as ethylene-acrylate elastomers (trade name Vamac) [Hagman and Crary, 1985]. A small amount of an alkenoic acid is present to introduce sites (C=C) for subsequent crosslinking via reaction with primary diamines (Sec. 9-2d). These elastomers have excellent oil resistance and stability over a wide temperature range (—50 to 200°C). They are superior to nitrile and chloroprene rubbers. Although not superior to silicone and fluorocarbon elastomers, they are less costly uses include automotive (hydraulic system seals, hoses) and wire and cable insulation. 

Additional curing is often achieved with sulfur, peroxide, or maleimide formulations. Chloro-sulfonated polyethylene has improved resistance to oil, ozone, and heat compared to many other elastomers. Applications include harrier membranes and liners, surface coatings on fabrics, automobile air-conditioner hose, electrical cable insulation, and spark-plug boots [Andrews and Dawson, 1986],... 

Abrasion resistance and solder iron resistances are two other important properties required from a wire and cable insulator. These properties are critical for polymers used as sheathing or jacketing for hookup wire. Cross-linking improves both of thern. ... 

PVC, another widely used polymer for wire and cable insulation, crosslinks under irradiation in an inert atmosphere. When irradiated in air, scission predominates.To make cross-linking dominant, multifunctional monomers, such as trifunctional acrylates and methacrylates, must be added. Fluoropolymers, such as copol5miers of ethylene and tetrafluoroethylene (ETFE), or polyvinylidene fluoride (PVDF) and polyvinyl fluoride (PVF), are widely used in wire and cable insulations. They are relatively easy to process and have excellent chemical and thermal resistance, but tend to creep, crack, and possess low mechanical stress at temperatures near their melting points. Radiation has been found to improve their mechanical properties and crack resistance. Ethylene propylene rubber (EPR) has also been used for wire and cable insulation. When blended with thermoplastic polyefins, such as low density polyethylene (LDPE), its processibility improves significantly. The typical addition of LDPE is 10%. Ethylene propylene copolymers and terpolymers with high PE content can be cross-linked by irradiation. ... 

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