Tracking resistance

Hazel [2] has discussed the phenomena of tracking and arcing in plastics used in electrical applications. He states that electrical tension may cause a tracking current to flow on plastic surfaces, especially if they are contaminated with humidity, dirt or chemicals, and irregular interruptions can occur along this current path, which may be caused by evaporating liquids. 

Arc resistance is closely connected with tracking resistance. Under the influence of an arc (which in practice may be generated by a short circuit) the plastic should not form a conductive bridge and should, if possible vaporise, so as to extinguish the arc. 

Similarly, a glow-wire simulates a source of ignition. The glow-wire test according to VDE 0471-2-10 [4] provides information about whether an object, such as an overheating conductor, could be a fire hazard in an electrical apparatus. 

The apparatus supplied by ATS FAAR (Table 5.1) evaluates, during a short period of time, the low-voltage ( 600 V) track resistance (or comparative tracking index) of insulating materials. 

The tracking resistance test is conducted by applying two electrodes—with a force of 1 N—to the surface of the specimen. A 0.01% solution of ammonium chloride is 

Kevlar para-aramide fibers have been shown to have three times the tracking resistance of general-purpose rubber [36]. Sechin et al. [37] carried out tracking resistance measurements on polyaniline-cerium oxide composites. 

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Key properties of alkyds are dimensional stability, colorability, and arc track resistance. Chemical resistance is generally poor. 

Nylons have excellent arc and tracking resistance. Arc resistance is not affected by moisture or temperature up to about 100°C. Comparative... 

The use of ABS has in recent years met considerable competition on two fronts, particularly in automotive applications. For lower cost applications, where demands of finish and heat resistance are not too severe, blends of polypropylene and ethylene-propylene rubbers have found application (see Chapters 11 and 31). On the other hand, where enhanced heat resistance and surface hardness are required in conjunction with excellent impact properties, polycarbonate-ABS alloys (see Section 20.8) have found many applications. These materials have also replaced ABS in a number of electrical fittings and housings for business and domestic applications. Where improved heat distortion temperature and good electrical insulation properties (including tracking resistance) are important, then ABS may be replaced by poly(butylene terephthalate). 

One disadvantage of many of these materials, however, is their rather poor electrical tracking resistance. 

The heat and flame resistance coupled with good electrical insulation characteristics, which includes in some grades good arcing and arc tracking resistance, has led to PPS replacing some of the older thermosets in electrical parts. These include connectors, coil formers, bobbins, terminal blocks, relay components, moulded bulb sockets for electric power station control panels, brush holders, motor housings, thermostat parts and switch components. 

Although the structure is polar much of the polarity is frozen in at normal service temperatures. In such conditions electrical insulation properties are quite good even at high frequencies. As with many aromatic polymers, tracking resistance leaves something to be desired. 

Compared with the phenolic resins they have a better colour range, track resistance and scratch resistance. They have a similar order of heat resistance, although their dimensional stability when exposed to hot dry conditions is not so... 

Good electrical insulation properties with exceptional tracking resistance for an engineering thermoplastic and, in particular, for an aromatic polymer. In tracking resistance most grades are generally superior to most grades of polycarbonates, modified PPOs, PPS and the polyetherimides. 

Good electrical insulation properties with a high dielectric strength and good microwave transparency but with a low tracking resistance typical of aromatic polymers with a high C H ratio in the structure. 

The cycloaliphatic resins also are clearly superior in arc resistance and arc track resistance. This has led to applications in the tension insulators, rocket motor cases and transformer encapsulation. 

Resistance to commonly prescribed antimicrobials such as the penicillins and macrolides/azalides increased dramatically in the late 1980s through the middle to late 1990s. Table 68-2 provides resistance information collected nationally from 1999 to 2004 using the Tracking Resistance in the US Today (TRUST) surveillance database.26 In 2004, the average national rate of resistance to penicillin and macrolides was approximately 18% and 25%, respectively. Susceptibility results alone do not account for clinical success or failures when treating pneumonia. 

Tracheobronchitis effect on heart, 5 107 Trachoma, 74 338 Tracking resistance testing, 79 587 Traction, 3 726-727 Traction thickener, 22 65 Trade... 

Alkyd molding compounds, when molded into finished parts, may have excellent arc resistance (180 sec. minimum) and excellent arc track resistance. Other good electricals such as dielectric strength and insulation resistance can be obtained. The filler combinations may also result in excellent dimensional stability and outstanding retention of electrical and physical properties after exposure to elevated temperatures (450°F.) for long periods of time. Water absorption values are extremely low, which helps to maintain electrical values. 

Parts molded from melamine compounds have a hard scratch resistant surface, practically no odor or taste, good electrical properties, fair arc track resistance, decorative appearance, and color fast characteristics. 

The specific gravity range is from 1.45 to 2.00. The principal use of melamine compounds has been in the dinnerware field. They are widely used in electrical switch gear applications where arc track resistance is very important. In some cases the melamine phenolic compounds are used to produce electrical switch gear where arc track requirements are not so severe. Other applications are ignition systems (distributor cap), housings, and other decorative applications. 

Resistance or resistivity Surface charge Electric strength Tracking resistance Power factor and permittivity... 

The nonaromatic nature of these maicrials provides for improved uv resistance and arc-track resistance compared to conventional epoxies The best properties arc generally achieved with anhydride and phenolic curing agents. 

Alkyds are formulated from polyester resins, cross-linking monomers, and fillers of mineral or glass. The unsaturated polyester resins used for thermosetting alkyds are the reaction products of polyfunctional organic alcohols (glycols) and dibasic organic acids. Key properties of alkyds are dimensional stability, colorability, and arc track resistance. Chemical resistance, however, is generally poor. 

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