Contact Voltage in the Urban Landscape:A Public Safety Hazard

Presentation to NASUCA

November 15, 2010

Atlanta, GA

Connie O. HughesConnie O. HughesFormer NJBPU President & CommissionerFormer NJBPU President & Commissioner

VP, Regulatory Affairs, Power Survey CompanyVP, Regulatory Affairs, Power Survey Company

David KalokitisDavid Kalokitis Senior Member IEEESenior Member IEEE

Section Coordinator IEEE Stray Voltage Working GroupSection Coordinator IEEE Stray Voltage Working GroupCTO, Power Survey CompanyCTO, 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.

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

Causes of Contact Voltage

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)

Aging infrastructure

• Expected life – 30 years

• Thermal, chemical, mechanical failure

• Abrasion against metal support racks

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

Contact Voltage in Urban Areas Across the US

Electric Distribution: Secondary System

Circuit Breaker

Circuit Breaker

Switchgear

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

Contact Voltage Examples

Part of Landscape

Public Proximity

Reliability Problems

33V found on mailbox caused by burned

service leg underground.

108V found on streetlight on beach. Repaired corroded

neutral.

60V found on sidewalk & front lawn. Service

replaced.

Common Energized Structures

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

• Fences

• Roadways

• Bus Shelters

• Access Hatches

• Phone Kiosk

Test Procedure and Process Comparison

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 speedMANUAL MOBILE

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

Detect Confirm

Classify Document

Evaluation of Energized Structures

Detection process has evolved to target cases of contact voltage and provide utilities with actionable and documented findings

Key Concepts

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

Summary of Concerns

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

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