An elementary book on electricity and magnetism and their applications . central stations to the substationsor other points for retail distribution isusually copper or aluminum. Sometimesconductors consisting of a steel center withcopper or aluminum outside are used wherelong spans are desirable and mechanicalstrength of conductor is required. Forvoltages up to 50,000 wooden polesare used. These are usually of whitecedar or chestnut, though in someparts of the country they are madeof pine, cypress, and tamarack, orother woods. Figure 298 shows thetop of a wooden pole with pin insula-tors. For
An elementary book on electricity and magnetism and their applications . central stations to the substationsor other points for retail distribution isusually copper or aluminum. Sometimesconductors consisting of a steel center withcopper or aluminum outside are used wherelong spans are desirable and mechanicalstrength of conductor is required. Forvoltages up to 50,000 wooden polesare used. These are usually of whitecedar or chestnut, though in someparts of the country they are madeof pine, cypress, and tamarack, orother woods. Figure 298 shows thetop of a wooden pole with pin insula-tors. For higher voltages, pin insu-lators become very large so that thesuspension type of insulator has to beused and these are suspended fromsteel towers, as shown in figure protect the line against lightning,it is usual to run a steel wire alongparallel to the power wires, and toground this wire at every tower. In large cities more and more elec-tric conductors are being placed underground. This method isof course expensive because it requires a stranded copper cable. Fig. 299. — Steel tower withsuspension insulator. 424 ELECTRICITY AND MAGNETISM
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectmagnetism, bookyear19
