Question

electric cables laid in summer are left a little loose. why?

Answer 1

Because the copper wire at the heart of the wire expands slightly - making the wires longer. since they are fixed at both ends, the wires sag due to the slight increase in length.

Answer 2

One of your example is


Why are the telephone wires kept slightly loose when they are laid in summer?

Telephone and electric wires stretch (expand) when the weather is hotter. Conversely, in the winter they shrink. Without some slack, they could become too tight and break, or pull loose from their anchors.