Download Contact Voltage

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
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
Aging infrastructure
• Construction dig-in
• Expected life – 30 years
• Duct collapse
• Thermal, chemical, mechanical failure
• Tampering by the public
• Abrasion against metal support racks
• Vehicle damage
Workmanship
• Unintentional damage
• Material not designed for subsurface use
• Improper treatment of dissimilar metals
• Improper wiring (reversed polarity)
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
Switchgear
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
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
• Fences
• Sidewalks
• Roadways
• Street Lights
• Bus Shelters
• Traffic Signals
• Access Hatches
• Parking meters
• Phone Kiosk
• Street signs
Test Procedure and Process Comparison
Manual Testing
Mobile Detection
Inaccurate – highly dependent on
testers’ body and hand position,
frequent false negatives
Accurate – sensitive to 1V or less at
30 ft, operator verifies findings
Incomplete – only tests listed assets
Complete - surveys entire area
No way to detect underground failures Detect voltage on metal or pavement
Slow – walking speed
Fast – driving speed of 25 mph
MANUAL MOBILE
Locating Contact Voltage
Mobile Detection
– Detects energized objects at a distance
– Performance certified by Independent lab
– Over 50,000 energized structures found
SVD2000 Mobile Contact Voltage Detection System
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
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