Estimating the Height of a Suspended Wire

Abstract

Estimating the height of a wire above the ground is a task that may be required to avoid contacting electrical distribution lines with ladders, antennae, long poles, or other reach extending devices. It has been suggested that this task is difficult because wire is often presented against the homogeneous field of the sky. The accuracy of estimations under this condition may be poor when made on an absolute basis, that is using an internal frame of reference. However, accuracy should improve when the estimation is made on a relative basis, using some external frame of reference. In order to assess the accuracy of such estimations, forty subjects were each asked to give a verbal estimate of the height of a suspended wire, as well as to match the wire height using a horizontal reference pole and a vertical reference pole. As expected, the verbal, or absolute, estimates had a higher average percent error (17.1%) than the relative horizontal estimates (7.7%). Relative vertical estimates produced the most accurate values, within about 2.0% of the actual wire height. The degree of accuracy observed in subjects using external references suggests that the ability to avoid contact with overhead electrical distribution lines may be high, given appropriate knowledge, attention, and motivation.