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The extensive tests reported herein have provided additional data on cable-sheath performance characteristics which readily can be applied to design practice by published methods.8,9,10 These data indicate: 1. Bending strain is the important consideration in determining sheath life of expansion loops in manholes. 2. If bending strains are low (cables of small diameter, lightly loaded, or cables in large manholes permitting large training radii), copper-lead or thin-wall alloy sheaths are satisfactory. 3. As cable diameter or loading increases, other factors being equal, strain increases. 4. Small expansion loops in restricted manholes increase the strain. 5. If bending strain exceeds a certain value, copper-lead will have a short life, and alloy sheaths should be used. 6. If the maximum permissible strain for standard alloy sheath is exceeded, additional strain resistance is best obtained by increased sheath thickness. 7. If bending strains are too high, the sheath increases in diameter, develops wrinkles and may fail from expansion rather than bending fatigue. 8. Thin-wall sheaths, in addition to lower resistance to bending and internal pressure, tend to wrinkle from handling. These wrinkles may cause stress concentrations and nonuniform bending resulting in short sheath life. 9. F-3 alloy is further substantiated as a superior sheathing material by this extension of previously published data.
American Institute of Electrical Engineers, Transactions of the (Volume:70 , Issue: 2 )
Date of Publication: July 1951