Transmission lines often pass near residential and commercial areas as well as over road crossings and parking lots, as shown in Figure 13.1. These energized transmission lines induce voltages on any conductive surface under or near them. If these surfaces are solidly grounded, their acquired charges from the power lines are continuously dissipated into ground and their potentials are low. However, if they are isolated or poorly grounded, they can accumulate enough charges to elevate their potentials to uncomfortable or even hazardous levels. In severe cases, it could reach levels that produce secondary shocks to any person touching the surface while standing on a grounded object. The magnitude of this induced voltage depends on several factors such as the voltage level of the energized lines, the proximity of the surface to the line, and the humidity in the air.