Overhead shield wires—also known as guard wires or shield wires—are used in overhead power lines to protect the current-carrying conductors from damage. These wires are uninsulated and do not carry electrical current; instead, they serve to shield the conductors responsible for power transmission. During installation, they are positioned above the conductors to intercept lightning strikes. Ideally, they are mounted at the highest point of the transmission towers so that, in the event of a lightning strike, the resulting current is safely conducted to the ground via the tower, thereby preventing damage to the power conductors.
These shield wires are made of steel and consist of 7, 19, 37, or more strands. Common designs are specified in the ASTM B416 standard; while aluminum-clad steel strands are often used to prevent corrosion, designs based on ACSR conductor cores (modified for shield wire applications) are also employed. Additionally, galvanized steel strands are used, as they offer lower costs and higher tensile strength.