. American hydroelectric practice; a compilation of useful data and information on the design, construction and operation of hydroelectric systems, from the penstocks to distribution lines . s in a rec-tangular formation which gives thewidest separation. These may beplaced two above and two below thepower conductors, or two above and oneeach side about on a level with the twolowest power conductors. Where asingle ground wire is used it should be placed as near as practicable to the power conductors. When two groundedwires are used they should be separated as far apart as possible and as faras
. American hydroelectric practice; a compilation of useful data and information on the design, construction and operation of hydroelectric systems, from the penstocks to distribution lines . s in a rec-tangular formation which gives thewidest separation. These may beplaced two above and two below thepower conductors, or two above and oneeach side about on a level with the twolowest power conductors. Where asingle ground wire is used it should be placed as near as practicable to the power conductors. When two groundedwires are used they should be separated as far apart as possible and as faras practicable should be on opposite sides of the power conductors. Thiswill reduce to a minimum the transfer of surge energy to the power conduc-tors. Protection against the splitting of poles may be secured by verticalconductor which runs the height of the pole and has one end buried in theground. Every fifth pole protected in this way serves as a protection froma direct bolt of lightning. A position of four ground wires recommended * Theory of Parallel Grounded Wires and Production of High Frequencies in Trans-mission Lines. by E. E. F. Creighton, A. I. E. E. Proceedings, June, Fig. 119.—Position of Four GroundWires when Non-Grounded Pins areUsed k 216 HYDROELECTRIC PRACTICE by Dr. E. E. F. Creighton where non-grounded pins are used is shown inFig. 119. To preserve the insulation afforded by the wooden cross arm themetalHc connections of the laterally grounded wires are carried free of thecross arm. At one point in the circuit is shown a series resistance to bringthe total resistance in the grounded loop up to a value at least equal toone-fifth of the critical damping resistance. Size of Ground Wire.—From a mechanical standpoint the size of groundwire is dictated by the length of the span. To guard against sleet, practiceseems to call for a ^g in. stranded Siemens-Martin steel wire for a span of600 feet and }/i in. for a span of about 250 feet and ordinary telegraph
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