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Contact Voltage in the Urban Landscape: A Public Safety Hazard Presentation to NASUCA

Learn about the hazards of contact voltage in urban areas and how to detect and address potential safety risks. Includes examples, case studies, detection methods, and key concepts.

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Contact Voltage in the Urban Landscape: A Public Safety Hazard Presentation to NASUCA

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  1. Contact Voltage in the Urban Landscape: A Public Safety Hazard Presentation to NASUCA 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

  2. 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.

  3. Properties of Contact Voltage • Contact voltage is a failure in a distribution system • Aging Infrastructure • Construction damage • Vehicle hit damage • Workmanship • Public safety concern • Hazard to public (human and animal) • Reliability concern • Initial

  4. 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)

  5. Where is Contact Voltage Found? • Contact voltage occurs in underground electric distribution systems • Extensive buried infrastructure in public spaces • Urban, populous areas most at risk • Heavy foot traffic • Public recreation areas with pets and children • Numerous unmetered underground services • Rural and suburban distribution is low risk • Mostly overhead or short underground runs • Less susceptible to damage from heavy vehicle traffic, tampering • Fewer busy public spaces

  6. Contact Voltage in Urban Areas Across the US

  7. 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

  8. Case Study: St. Catherine’s Church • 112V on fence • Service duct cracked by tree roots under sidewalk

  9. Contact Voltage Examples 33V found on mailbox caused by burned service leg underground. Part of Landscape Public Proximity Reliability Problems 108V found on streetlight on beach. Repaired corroded neutral. 60V found on sidewalk & front lawn. Service replaced.

  10. Underground infrastructure can fail or sustain damage at any time and energize objects in the public landscape Manholes Sidewalks Street Lights Traffic Signals Parking meters Street signs Common Energized Structures • Fences • Roadways • Bus Shelters • Access Hatches • Phone Kiosk

  11. 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

  12. SVD2000 Mobile Contact Voltage Detection System Locating Contact Voltage • Mobile Detection • Detects energized objects at a distance • Performance certified by Independent lab • Over 50,000 energized structures found

  13. 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

  14. 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

  15. Contact voltage exists in all distribution systems CV is the product of a fault or failure Protection devices largely non-existent Voltage can change suddenly Where detection is performed, density of CV findings is high Electric distribution systems should be swept for leaks much like gas and other distribution systems Summary of Concerns

  16. Regulatory Activity Related to Contact/Stray Voltage(not farm-related) • Massachusetts: regulation • New York: regulation; regularly reviewed and modified • New Jersey: docketed and deferred pending additional information

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