The mechanical advantages of the compound wire are also very great. The labor of handling and stringing a light wire is much less than when a heavy one is employed. In running the wires over buildings, a mode of construction which has become very common in all large cities, stretches may safely be made double the length of those taken with the ordinary wire, and yet with less strain upon the insulators. Another important point in favor of this wire is the imperishable nature of the copper, which is the exposed metal. Copper, under the same conditions, remains wholly unimpaired.
Many cases occur in the construction of lines in which transportation is an item of great expense.
In such cases, wire of the same or greater conductivity than galvanized iron, weighs materially less, with no disadvantage whatever arising from its lightness. The following table exhibits the weight, size, and relative strength of compound wires, equivalent in conducting power to the ordinary sizes of iron wire used in telegraphic construction. Galvanized Iron Wire. Compound Steel and Copper Wire. The term relative strength, used in the preceding table, is the quotient obtained by dividing the strain which would break the wire by its weight per mile.