Development of an overhead power line contact alarm for mobile equipment

Abstract

This paper describes research by the US National Institute for Occupational Safety and Health's Pittsburgh Research Laboratory to develop an overhead power line contact alarm system for mobile equipment. Analysis of accident reports revealed that many workers were unaware of a power line contact until after an injury occurred, suggesting that many injuries could be prevented by an alarm system that alerts operators and other nearby workers when a line has been contacted. Sensing electric current flow through mobile equipment chasses and measuring electric field strength between equipment chasses and ground were studied as possible techniques for detecting power line contact. Experiments involved using these techniques to monitor energised cranes and dump-bed trucks, operating on commonly encountered types of road and work area surfaces. Sensing current flow proved inadequate when operating on a high-resistivity surface such as asphalt, but electric field measurement was more reliable, performing well on several different surface types. Additionally, electrical characteristics of the cranes and trucks were examined, and this confirmed that, in a power line contact accident, the primary hazard to personnel is simultaneously contacting the equipment and ground. A prototype power line contact alarm system was constructed and tested.