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Trial Use Guide For
Assessing Voltages At
Publicly and Privately
Accessible Locations (P1695)
Section 6 Contact Voltage
Scott Kruse
Power Survey Company
[email protected]
973-634-7268
David Kalokitis
Power Survey Company
[email protected]
973-986-5448
January 12, 2009
Presentation Overview
• Objectives
• Time Frame
• Description of effort to date
• Outline of draft text
• Feedback
• Discussion
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Objectives
Distribution of Section 6 Contact Voltage to all
group members through e-mail.
Post on Working Group website
http://grouper.ieee.org/groups/td/dist/stray/
All interested parties to read and provide
feedback by sending word doc. with tracked
changes and / or comments.
Submit feedback to:
Dave Kalokitis: [email protected]
Scott Kruse: [email protected]
Chuck DeNardo: [email protected]
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Time Frame
• Submit any edited text or comments by the
end of April for inclusion into the next
revision of the document.
Effort to date
• A small number of contributors have
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generated and mutually reviewed draft
22 pages
Many openings for needed contributions
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6.1 Contact Voltage
Shock
e
fa c
Hu
ur
dS
ma
n
ize
rg
/A
ni m
al
e
En
• Definition
• General Concerns
• Shock Hazard
• Shock Triangle
Ground
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6.1.1 Contact Voltage
Discovery
Energized Surfaces are often discovered by:
• Incident
• Shock Report from Public / Other
• Inspection
• Scheduled inspection and test of assets
• Detection
• Manual Survey of Assets
• Mobile Detection of Energized Surfaces
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6.2.1 Contact Voltage Root
Causes
• Insulation Degradation
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• Failure of insulating materials
Neutral Corrosion / Burn Out
• Current may return through ground
• Neutral to earth voltage (NEV) due to resistance
Workmanship
• Reversed polarity
• Improper insulation of connections
Construction Damage
• Excavation, Road work, Improper Repair of Damage
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6.2.2 Energized Structures
• Manhole Covers
• Hand Hole Covers
• Street Lights
• Traffic Signals
• Sidewalk / Roadways
• Gates / Fences
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6.3.1 Test and Measurement
Equipment
• 6.3.1.1 Hand Held Detector
• 6.3.1.2 Mobile E-field Detector
• 6.3.1.3 Hand Held E-field Detector
• 6.3.1.4 Voltmeter
• 6.3.1.5 Ground Lead
• 6.3.1.6 Switchable Shunt Resistor
• 6.3.1.7 Ground Rod
• 6.3.2 Safety Equipment
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6.3.4 Locating, Measuring and
Mitigating Contact Voltage
• 6.3.4.1 Discovery Methods
• 6.3.4.1.1 Incident
• Record Keeping, Communication
• 6.3.4.1.2 Inspection
• Prescribed cyclic inspection of assets
• Record Keeping
• 6.3.4.1.3 Detection – Underground/Overhead
• 6.3.4.1.3.1 Manual Survey
• 6.3.4.1.3.2 Mobile Detection
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6.3.4.2 Measurements
• What is the voltage level on the
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energized surface?
Is the voltage supplied through low or
high impedance?
How much current can be sourced?
Is the voltage related to a fault, neutral
resistance, or other condition?
Is the voltage likely to change?
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6.3.4.2.1 Measurement Circuit
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6.3.4.2.2 Voltage Measurements
Open circuit voltage measurements
Reference must not be energized
Rsource
~
Voltmeter
AC Source
Rshunt
Reference Ground
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6.3.4.2.3 Current Measurements
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Closed circuit (shunt voltage) measurements
Reference must not be energized
Reference and contact impedance must be low
AC Source
Rcontact
Rsource
Rcontact
Voltmeter
Rground
~
AC Source
Rshunt
Reference Ground
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6.3.4.2.3 Current Measurements
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Key Concepts
Determine
Rsource
Minimize
Rground
Rcontact
Rcontact
Rsource
~
Rcontact
Voltmete
r
AC
Source
Rground
Rshunt
Reference Ground
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Use Pushbutton Shunt
Compare open and closed circuit voltages
Try alternate ground (earth) points
Interpret results, know when to conclude measurements
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Interpret Results
• Assume ground and contact resistances
low
• High Voc (50 Volts)
• Safe?
• Low Voc (3 Volts)
• Safe?
Low Vcc (0.9 Volts)
Low Vcc (2 Volts)
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Interpretation only possible when:
• Steps are taken to confirm low ground
and contact resistance and ground is not
energized
• Voc Open Circuit Voltage measured
• Vcc Closed Circuit Voltage measured
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Shunts & Grounds
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Shunt should eliminate phantom voltage
500 ohms – low impedance
Important to find low impedance ground
3000 ohms – eliminates phantom voltage
If: Ground impedance = 50 ohms
Then: Measurement error –
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10 % with 500 ohm shunt
1.6% with 3000 ohm shunt
Understand importance of ground impedance
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Next Steps (for this section)
• Additional measurement scenarios
• Analysis of data
• Specific examples
• Additional measurements and their utility
• NEV treatment
• Structure specific information
• INPUT WELCOME
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6.3.4.2 Safety Standards
The New York State Electric Safety
Standards currently state the following:
Structures with voltage that measures 1
volt or greater with a 500 ohm shunt
should be barricaded and guarded until
properly mitigated. Any temporary repair
should be periodically monitored until
permanent repair is made.
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6.4 Mitigation
• Typical repairs by structure type
• Unusual findings
• Trends
• INPUT WELCOME
6.5 Case Studies
• INPUT WELCOME
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