Wire insulation volume resistivity

Excitable tissue, when activated, will be found to generate currents both within itself and also in aU surrounding conducting media. The latter passive region is characterized as a volume conductor. The adjective volume emphasizes that current flow is three-dimensional, in contrast to the confined onedimensional flow within insulated wires. The volume conductor is usually assumed to be a monodomain (whose meaning will be ampHfied later), isotropic, resistive, and (frequently) homogeneous. These are simply assumptions, as will be discussed subsequently. The permeabihty of biologic tissues is important... 

There are three broad classifications for rigid PVC compounds Type II, chlorinated polyvinyl chloride (CPVC), and Type I. Type II differs from Type I due to greater impact values, but lower chemical resistance. CPVC has greater high temperature resistance. These materials are considered unplasticized, because they are less flexible than the plasticized formulations. PVC has a broad range of applications from high volume construction related products to simple electric wire insulation and coatings. CAS numbers are 9002-86-2, 8063-94-3, 51248-43-2, and 93050-82-9. 

Metakaolin is an effective functional filler in plasticized PVC wire insulation at loadings of about 10 phr. It better protects the insulation from cracking or treeing, a term that describes the physical breakdown of the cable polymer matrix due to moisture or other external influences. Volume resistivity greatly improves when metakaolin is incorporated compared to other minerals (see Table 13.9) [15], although the color is not as white as with higher temperature fully calcined kaolin. In addition,... 

Table 10.8 shows electric strengths. Table 10.9 shows volume resistivities, Table 10.10 shows dielectric constants, and Table 10.11 shows dissipation factors for coatings using most of the available resins. Magnet wire insulation is an important use for organic coatings. National Electrical Manufacturer s Association (NEMA) standards and manufacturers trade names for various wire enamels are shown in Table 10.12. This information can be used to guide the selection of coatings. However, it is important to remember the aforementioned warnings about blends of various resins and the effects on performance properties.

Water-washed calcined clays vary in particle size and degree of calcinations. The primary use of calcinated clays is in wire and cable insulation. Use of small amounts of partially calcined clay in polyvinyl chloride (PVC) can double volume resistivity. A secondary use of calcined clays in PVC and other polymers is extending titanium dioxide (TiOj). Calcined clay can replace up to 20 percent of the T1O2 without loss of optical properties. 

Eleetrieal properties of biodegradable polylactic acid films were measured and compared with those of erosslinked polyetlylene (XLPE) cimently used as insulation for cables and electric wire [10]. The volume resistivity, dielectric constant and dielectric loss tangent of PLLA were found to be almost the same as those of XLPE. However, the impulse breakdown strength of PLLA was 1.3 times that of XLPE. 

The largest volume of polymeric materials used for wire and cable insulation is thermoplastics, namely polyethylene (PE) and polyvinylchloride (PVC),4 and, to a lesser degree, elastomeric compounds. The main reason for the prevalence of the PE and PVC in wire and cable insulation is their easy processing and relatively low cost. However, their main disadvantage is that their physical properties, such as plastic flow at elevated temperatures, environmental stress cracking, poor solvent resistance and low softening temperatures,3 cannot always meet demands imposed on them by modern applications. Cross-linking of these materials improves their... 

One of the larger uses is for wire and cable insulation. The flame resistance makes this the material of choice for residential wiring, extension cords, and so on. Inexpensive garden hose represents another large-volume use. Sports balls can be produced by rotational molding of plastisols. The low fabrication cost allows such products to dominate the lower-price-range market.76-77... 

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

Low-permittivity ceramics are widely used for their insulative properties. The major requirements are good mechanical, thermal, and chemical stability good thermal shock resistance low-cost raw materials and low fabrication costs. These include the clay- and talc-based ceramics also known as electrical porcelains. A large-volume use of these materials is as insulators to support high tension cables that distribute electric power. Other applications include lead-feedthroughs and substrates for some types of circuits, terminal connecting blocks, supports for high-power fuse holders, and wire-wound resistors. 

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