Handling Wires On The GroundThe Ground

EEI Occupational Safety and HealthSafety and Health

Committee October 7 2009October 7, 2009

Review AEP’s Evolution of Handling Wires on Ground PolicyWires on Ground Policy

• AEP and CSW had different requirements for workers handling wires on the groundworkers handling wires on the ground connected to the system after protective grounds had been installed

• CSW adopted a policy in 1997 requiring rubber glovesg

• AEP had no company wide requirement, but some Operating Companies required hot linesome Operating Companies required hot line overshoes and/or rubber gloves be worn

In 2002 3 a new AEP system wide policy was• In 2002-3 a new AEP system wide policy was adopted which required rubber gloves*

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* Handling wires on the ground without rubber gloves is allowed under certain conditions when wires are not connected to the system

Review AEP Studies Completed

• In 2005-6 AEP conducted tests to examineIn 2005 6 AEP conducted tests to examine the effectiveness of various distribution line jobsite grounding methods

• In 2008 AEP conducted tests on worksite shock protection in conjunction with Dr. Tom Glavinich, University of Kansas

• In 2008 AEP Appalachian Power Company cond cted tests to determine the magnit deconducted tests to determine the magnitude of voltages to which workers may be exposed when working on lines with missing

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exposed when working on lines with missing primary neutral conductors

Review AEP Studies Completed

Thresholds For Human ReactionThresholds For Human Reaction To Electric Shock*

• 1.2 milliamps can cause a slight tingle

• 10 milliamps can cause muscle contraction

• 30 milliamps can cause respiratory failure

• 250 milliamps can cause heart fibrillation

4* From the Electrical Safety Handbook Second Edition Source Ralph Lee

Review AEP Studies Completed

– The 2005-6 AEP tests were conducted using a gsimulated line mechanic working from a wood pole with a few tests with worker working from ground

– Different wood poles were used (new and aged; creosote, CCA and penta treated; wet and dry conditions) using a single-point ground in combination ) g g p gwith a range of grounding techniques:

HV P b

HAND

Body Impedance

HV Probe

10 ΩShunt

SimulatedGaff

Simulated LineSi l t d Li M h i

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Simulated Line Mechanic Hands On Pole

Simulated Line MechanicWorking On Pole

Review AEP Studies Completed

2005 Test showing simulated Line Mechanic on ground handling downed conductor

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Review AEP Studies Completed

Current Through Simulated Line Mechanic Handling WireCurrent Through Simulated Line Mechanic Handling Wire On Ground With No Safety Or Pole Ground Equaled 8.5 Amperes at 19.9 kV* or 3.3 Amperes at 7.2 kV*

Safety G dGround

7* Extrapolated to 19.9 kV and 7.2 kV

Review AEP Studies Completed

Current Through Simulated Line Mechanic Handling Wire On g gGround With Single Safety Ground And Pole Ground Equaled

1.2 Amperes at 19.9 kV* and 500 Milliamperes at 7.2 kV*

Safety G dGround

Pole Ground

8* Extrapolated to 19.9 kV and 7.2 kV

Review AEP Studies Completed

• In 2008 AEP conducted tests on worksite shock protection in conjunction with Dr. Tom Glavinich, University of Kansas

• These tests examined step and touch potentials for a utility worker working onpotentials for a utility worker working on ground level under several different worksite configurations and examined the effectiveness of ground mats and rubber overshoes to mitigate worker exposures

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Review AEP Studies Completed

2008 AEP test - The current through a simulated Line2008 AEP test The current through a simulated Line Mechanic handling a wire on the ground with single safety ground (open neutral) equaled 464 Milliamperes*

Safety G dGround

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* Extrapolated to 7.6 kV with Line Mechanic (1000 ohm body impedance) 30 feet from pole ground

Review AEP Studies Completed

• In 2008 Appalachian Power Company conducted t t t d t i th it d f lt ttests to determine the magnitude of voltages to which workers may be exposed when the primary neutral was missing

• A four pole single phase tap test line with a 10 kVAtransformer with variable load and variable ground resistivity conditions was constructed to simulate

f

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various field conditions and measure current and voltages

Review AEP Studies Completed

• As expected, when the primary neutral was missing hazardous voltages were present undermissing hazardous voltages were present under many simulated field conditions

• The magnitude of voltages present are difficult to• The magnitude of voltages present are difficult to predict but are proportional to the drop in secondary voltage seen on services as the electrical load varieselectrical load varies

• Return current will follow all available paths such CATV d l h blas CATV and telephone cable messengers

• High earth resistivity results in higher voltagesHigh earth resistivity results in higher voltages (Example: 848 volts to remote earth with 280 ohm ground return path and 3 kW load)

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Review AEP Studies Completed

• The 2005 6 Dolan Lab tests revealed that if a line with• The 2005-6 Dolan Lab tests revealed that if a line with safety grounds installed becomes accidentally re-energized a worker could be exposed to hazardous voltage levels if they were on a pole near ground levelvoltage levels if they were on a pole near ground level or were on the ground handling conductors connected to the system

• The 2008 Dolan Lab tests were more extensive in examining step and touch potentials of workers on the ground The results were consistent with the findingsground. The results were consistent with the findings of the 2006 tests, i.e. a worker could be exposed to hazardous voltage levels if they were on the ground handling conductors connected to the systemhandling conductors connected to the system

• The 2008 Appalachian Power tests confirmed

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hazardous touch potentials are possible if the neutral conductor is missing or open.

Review AEP Studies Completed

AEP Study Conclusions –AEP Study Conclusions • Tests revealed that if a line with safety

grounds installed becomes accidentallygrounds installed becomes accidentally re-energized, a worker could be exposed to hazardous voltage levels if they were g yon a pole near ground level or were on the ground handling conductors connected to the system

• Qualitative Analysis has confirmed these test results

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Questions

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Appendix

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Review AEP Studies Completed

Nomenclature:Nomenclature:Simulated Line Mechanic on Gaffs

Grounding

PhaseWire

Insulator

Hands

GroundingJumper

Neutral Bare Pole Ground

304/116 mA

1’

Molding

NeutralWire

Bare Pole Ground w/Staples Line

Mechanic

Extrapolated to 34.5/12 kV

1’

Gaffs

Height

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Ga s

Ground Rod

Review AEP Studies Completed‘Wet,’ Aged, Penta Pole TestsHands on wood (9/22/2006)Hands on wood (9/22/2006)

* Extrapolated to 34.5/12 kV

2/0 A20’

13/0 mA10’

15’2/0 mA

15’

304/116 mA*1’

-6’124/48 mA3’

8’

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