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. ,... ') i'tiJ 244, ~1 E T R 0 POll TAN W ATE R D [S T R 1 C T the other to the Iron Mountain, Eagle Mountain, and Hayfield plants. The present lines will deliver 165,000 kilowatts, or suffi- cient power for pumping one-half the ultimate capacity of the aqueduct. In the future a parallel line will be built from Boulder to Camino and probably extended to Hayfield. Preliminary studies to determine the most economic transmis- sion line included electrical stability calculations, and complete de- sign of towers and cost comparison of lines using two types of conductors. Long-time laboratory tests were made of different makes of insulators to select the one most suitable for the antici- pated conditions. Five types of towers were built, the standard suspension tower weighing 10,200 pounds and being capable of supporting a maxi- mum span of 1,710 feet. The dead end tower used at all angles above 10 degrees is the heaviest and weighs 14,800 pounds. The towers support the three conductors in a horizontal plane 22 feet 3 inches apart and 70 feet 6 inches above the ground, Towers were staked to provide an initial clearance of conductors to ground in mid span of 30 feet, somewhat above the legal requirement, to al- low for future stretch in the cable. The four legs of the steel towers are supported upon footings which must take the thrust or pull of the tower legs under condi- tions of high wind or with broken conductors. The soil of the des- ert is generally sufficiently alkaline to corrode exposed galvanized metal, consequently a type of footing was adopted which consists of a central leg angle attached to a structural steel grillage, the whole of which is encased in reinforced concrete. In the dry lake, however, greater precaution was necessary and there the towers were set upon concrete pads, supported by creosoted piling driven deep into the soil. The concrete pad is protected as much as pos- sible from the action of the strong alkalis by a coating of rich "sphaltic mastic. The conductor used uniformly over all the line, except in the 10- mile section across the Danby Dry Lake, where copper conductors were adopted as being more resistant to the corrosive action of alkali dust, is a composite cable made up of 26 aluminum wires stranded over a core of seven galvanized steel wires. The cross section of aluminum is 795,000 circular mils. The outside diameter is 1.108 inches and the weight is 1.09 pounds per linear foot. The copper conductor used over the Danby Dry Lake is made up of 50 copper wires stranded in two layers over a twisted copper j 1 1 I \