The simple answer is, "Gravity".
Gravity pulls the wires down just as it pulls everything else down. The wires can only be pulled with a maximum tension, and all the while gravity is pulling down.
CU this is the right answer by killerjo
They are not grounded therefore can not carry an electrical charge.
because of heat cables expand
The conductor strung between two towers is not as tight as a rod, but has some "sag". The conductor is bit loose between two towers. Generally the permissible sag is about 3% (In India)
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It is possible that the electrical wirings are grounded. You'll probably need to get an auto-electrician to take a look at it.
i know someones going to be on this sooooooooo....... they sag because the hydro workers know, from the heat the cbles will sag during the summer, so they start the sag so they cant sag anymore
by its wirings...... ^_^
This seems like a question from an electrical course, and is probably best answered by your course materials. It's your test question, not ours, and there won't always be someone to ask the answer of. Earn your diploma.
sag
CU noob
SAG