EoW July 2013

Technical article

transformers, conductors, switchgear, circuit breakers, physical clearances, cable terminations, safety warning signs, and protective clothing for workers installing electrical equipment. To provide for electrical safety, methods that determine the level of insulation resistance to transmission of electricity through various substrates have been developed (7) . One measure is volts per mil determined by ASTM D149 (8) . This method is a measure of the dielectric breakdown voltage and dielectric strength of the insulation. The value is high for a good insulation material. Another measure is dielectric constant (DC) or dissipation factor (DF) measured by fluid displacement using ASTM D1531 (9) . Electrical resistance to breakdown by treeing in insulation is measured by ASTM D3756 (10) . The value is low for a good insulation material. ASTM D4872 (11) is a test method for dielectric testing of wire and cable filling compounds. The inclined plane tracking and erosion test, ASTM D2303 (12) , or the dust and fog tracking and erosion resistance test, ASTM D2132 (13) , evaluate tracking resistance on the contaminated surface of an insulation material. b Physical Properties and Chemical Resistance – Tensile strength, elongation low temperature and room temperature impact, crush resistance, and additionally, oil, gasoline, and ozone resistance can be evaluated for the operating environment. Examples of performance standards that contain these performance properties are ASTM D470 (14) , UL 44 (15) and UL 83 (16) . c Flame and Smoke performance – Various levels are attained depending on the required level of safety. For cable, UL 44 contains FT1 – dripping particles, FT2 – horizontal and FT4 vertical tray fire tests for example. Additional examples of W&C fire and smoke performance tests are shown in Table 1. Electrical cable product fire safety performance has been evolving. Fire safety is partly based upon control of ignition, the rate of heat released, and flame spread or smoke released during a fire. These are critical measures and are evaluated by UL 1685 (25) and ASTM D5537 (23) , for example. The amount of heat released determines how quickly a fire can spread. Greater and more rapid heat release will overcome some fire resistant additives. More heat released creates a greater fire

fighting challenge for firefighters who arrive on the scene. Controlling the amount and intensity of the heat and smoke released will allow trapped people more time to escape safely and property damage may be less extensive. The level of smoke can obscure vision and inhibit or prevent people from escaping from a fire scene. There are standards designed to measure the level of smoke through standards such as UL1685 (25) , ASTM E662 (24) , or smoke obscuration measured by ASTM D5424 (21) . ASTM Standard D5485 (22) , first issued in 1994, addresses the corrosion of electronic systems as a result of fire damage. Loss of electronic systems can affect alarms and other critical systems in buildings. These revised and newer standards reflect the evolution toward better fire safety. d Temperature performance – 75 or 90ºC rating defines performance of cable for overload capability, or operating temperatures for example. 2.1.4 Electrical Fire Safety (27) Report issued by the US Fire Safety Administration The Problem : During a typical year, home electrical problems account for 26,100 fires and more than $2 billion in property losses. About half of all residential electrical fires involve electrical wiring. Statistically, December and January are the most dangerous months for electrical fires. Fire deaths are highest in winter months with more indoor activities, and increases in lighting, heating, and appliance use. The bedroom is the leading area of fire origin for residential building electrical fires. However, electrical fires that begin in the living room/family room/den areas result in the most deaths. The Causes of Electrical Fires : Most electrical distribution fires result from problems with “fixed wiring” such as faulty electrical outlets and old wiring. Problems with cords (such as extension and appliance cords), plugs, receptacles, and switches also cause many home electrical fires. Light fixtures and lamps/light bulbs are also leading causes of electrical fires. Many avoidable electrical fires can be traced to misuse of electric cords. These include overloaded circuits, poor maintenance, and running the cords under rugs or in high traffic areas for example. 2.1.5 Marketing Considerations Standards are necessary for business success. Having people who are standards experts in your organisation is essential.

Wire and cable and electrical equipment standards were not implemented until later in the century. Standards support the minimum properties required for safety and performance. Every three years the NEC is significantly revised to keep pace with technology and further enhance protection against electrical fire and shock hazards. The absence of, or poorly written, standards would significantly reduce the quality of life on earth. Good standards serve as a barrier to sub-standard products. Standards should bring value, be effective and not act as a barrier to free trade. You can help this process. 2.1.2 Value of Standards Development : Standards are developed by a consensus reached based upon input from a variety of interests. Producers, users, testing companies and customers each bring their perspective to the standards development process. This process adds value because it develops standards that are effective, relevant, and credible based upon the integrity of the developers (5) . influence standards. They evolve as wire and cable (W&C) technology changes. This makes all of us, as producers and users, important, with our input being vital for good standards to bring value and benefits. Wire and cable products meet demanding electrical test, physical, mechanical and chemical property performance criteria for a variety of rated temperatures. Standards development revolves around generation of performance data and information to permit safe practices during installation, testing and usage of wire and cable products. We expect these products to last for 30 or more years. ASTM was cited by The 1947 President’s Conference on Fire Prevention (6) for its recognition that performance rather than specific materials should decide the future course of fire safety. Performance allows for new materials developments to raise safety standards to the next level. 2.1.3 Benefits of Standards Development : a Safety – The NEC and ASTM, among others, provide practical guidance to help safeguard employees and the public from hazards during the installation, operation, and maintenance of electric supply and communication lines and associated equipment. The NEC covers a broad range of electrotechnical areas, including storage batteries, Advances in technology

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July 2013