In recent years, environmental issues have had a profound influence on cable designs and materials used in cable construction. This paper will address the issues concerned with the effects of cable on the environment, as well as, the effects of environmental conditions on cable performance and reliability. Effects on the environment include release of toxic materials and contamination of ground water. Environmental effects on cable are related to the presence of moisture, chemicals, ions, oils or solvents. All such issues must be considered in the evolution of environmentally safe cables. This also extends to the manufacturing processes for producing cable insulation, jacketing, and sheathing materials as well as the cable manufacturing process itself.
Lightning can cause damage to electrical systems from direct and induced effects. A study was conducted to devise means to prevent or control the effects of lightning on instrument and control systems. The results indicate that an acceptable approach is to use instrument cables with a relatively thick overall metallic shield grounded at both ends. The overall shield functions as a magnetic shield, not because of the mere presence of metal, but because it generates a counter, or opposition, c m n t that nearly cancels out the interfering current on the signal conductors. The data show that a twisted pair by itself is not adequate to protect against lightning. The overall shield is used in conjuiction with a single point ground system to provide this protection.
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