Contact Voltage in the Urban Landscape: A Public Safety Hazard Presentation to NARUC November 15, 2010 Atlanta, GA Connie O. Hughes Former NJBPU President & Commissioner VP, Regulatory Affairs, Power Survey Company David Kalokitis Senior Member IEEE Section Coordinator IEEE Stray Voltage Working Group CTO, Power Survey Company
What is Contact Voltage? • Contact Voltage - Elevated voltage on a publicly accessible structure or surface due to faults in buried or internal wiring. Public safety concern with contact voltage is the possibility of exposure up to line voltage, typically 120V or higher. • Contact Voltage exposure is NOT adequately gauged by a simple voltage test • Line faults are a serious shock hazard regardless of voltage present. Detection and investigation is necessary for safety.
Causes of Contact Voltage • Aging infrastructure • Expected life – 30 years • Thermal, chemical, mechanical failure • Abrasion against metal support racks • In-situ Damage • Construction dig-in • Duct collapse • Tampering by the public • Vehicle damage • Workmanship • Unintentional damage • Material not designed for subsurface use • Improper treatment of dissimilar metals • Improper wiring (reversed polarity)
Electric Distribution: Secondary System Switchgear Circuit Breaker Circuit Breaker • Secondary Distribution (<600V) • No protection against electric shock • No monitoring or failure indication • Utility notified of cable failure, fire, or shock incidents by the public or active testing
Case Study: St. Catherine’s Church • 112V on fence • Service duct cracked by tree roots under sidewalk
Mobile Detection Accurate – sensitive to 1V or less at 30 ft, operator verifies findings Complete - surveys entire area Detect voltage on metal or pavement Fast – driving speed of 25 mph Manual Testing Inaccurate – highly dependent on testers’ body and hand position, frequent false negatives Incomplete – only tests listed assets No way to detect underground failures Slow – walking speed Test Procedure and Process Comparison MANUAL MOBILE
Evaluation of Energized Structures Detection process has evolved to target cases of contact voltage and provide utilities with actionable and documented findings Detect Confirm Classify Document
Contact voltage is often sourced by line voltage Low Voltage findings are often indicators of a fault Specific tests help confirm source Know the source and know the hazard Detection methods work in all seasons People and pets more susceptible to shock in wet/snow/salt conditions Key Concepts