How often is a shield wire grounded?

• A. Every other structure
• B. At each structure
• C. Once every mile
• D. None of the above

Answer: (B)

Shield wires intercept lightning and must be grounded at every structure so there is a short, low-impedance path to earth. When a strike hits, the lightning current is diverted along the shield wire to the ground grid attached to the structure. Grounding at each structure keeps the shield near earth potential along the entire span, reducing the chance that the surge will raise voltages on the phase conductors or jump to insulators and other hardware. If grounding were done less frequently, long stretches of shield wire could become relatively floating during a strike, allowing higher voltages to develop and increasing the risk of damage during lightning events. Therefore, the standard practice is to ground the shield wire at every structure.