One of the simplest and most widely used methods for increasing the resistance in the
accidental path is to cover the entire surface of the substation with gravel [30]. This
type of covering provides a high resistance barrier even under wet conditions but in
practice the integrity of the layer is often lost due to lack of maintenance and erosion
due to excessive vehicle travel. As an alternative or in addition to the gravel layer,
a plastic sheet can be placed under the ground surface [129]. If there are particular
routes in frequent use within an installation, wooden passageways can also provide
very good insulation.