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Home Radiofrequency Transmission Lines Mechanical Construction of Openwire Transmission Lines Wire Stringing  
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Wire StringingAuthor: Edmund A. Laport The tensile strengths of harddrawn copper and copperclad steel wires are given in many handbooks and commercial catalogues.
The relations between span, sag (or dip), wire size, and tension are given in the following equation,
in which S is the sag in feet, W the weight of the wire in the span, L the span length in feet, and T the tension in pounds.
The tension of the wire loaded only by its own weight can then be calculated from the same equation. This tension can then be measured with a dynamometer during stringing or by timing the natural period of vibration of the wire and applying the following equation, in which T is the tension in pounds as derived from the previous equation and t is the time in seconds for N complete fundamental vibrations of the whole span.This measurement is made as follows: Snap the wire at its midpoint by pulling it to one side and releasing it. At the moment of release a stop watch is started, and the number of complete swings of the wire are counted (say 10 vibrations), at which moment the watch is stopped. Applying this information to the foregoing equation gives its tension. Most wires when stressed appreciably will stretch slightly. This stretch is a partial allowance for contraction at lower temperatures.
Guy wires can be correctly stressed using the same formulas. There are three classes of loading used to design pole lines, designated as shown in Table 4.5.


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