Why are thin wires strung along the tops of high-voltage transmission towers?

Dear Cecil:

You know those high-voltage power lines you see on towers? They're big and thick and they're hung on big insulators. But at the very top of the towers I also see one or two thin wires that aren't on insulators. What are they for?

Cecil replies:

Dear Mike:

Lightning protection. Called "static lines," the wires are grounded at intervals and basically function as continuous lightning rods, attracting lightning bolts and conveying them around the current-carrying wires to the earth. Static lines are also used on telephone poles sometimes. The wire you see running down the pole, often sheathed in wood or some other insulator for the bottom ten feet or so, is the ground connection. Mess with it at your peril.

Send questions to Cecil via cecil@straightdope.com.

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