Girl Killed at Metal Light Pole
Alan Poudrier Response:
A wise person would collect as much evidence as possible, take
time to analyze all of the information that has been gathered, and possibly provide a
statement to support an educated explanation of what happened and perhaps offer some thoughts
as to what improved conditions might avoid future similar incidents.
Based on your comment, you appear too sharp (or focused) on
a mission to prove that grounding rods serve no purpose and you have a tendencies to make
quick and meaningless comments (a characteristic of being unwise).
The good part is, you have room to grow and you have indicated this ("Hey, I love it when Im wrong, because I get to learn something new so if you think a ground rod at a pole serves a purpose, provide me with information to support your thoughts" . . . . . "Your the first person to make sense. I agree that the better ground when a neutral is open reduces the touch potential on metal parts and increases the voltage at the light").
Mike Holts Response: Al your 100% correct with your comments and I am sorry that I did not take the time to be more careful (wise) and I will try to be more careful in the future.
The reason I sent the incomplete newsletter about the death of the young girl and my comment was my concern that a larger percentage of people think driving a ground rod and bonding it to a metal pole makes the installation safe from electric shock, when in fact it does not.
Personally I dont care if people drive ground rods at
metal poles (I just wished I knew why they did), Im just concerned that some might
think that a ground rod at a metal pole provides a back-up in case the primary
ground (equipment grounding conductor) is lost, which of course it does not.
From my "Illustrated Grounding" book: "Contrary
to the belief of many in the electrical industry, grounding metal parts of electrical
equipment to the earth does not assist in removing dangerous voltages from ground-faults
(line-to-ground faults) by opening the circuit overcurrent protection device for systems
that operate at less than 600 V! To understand this, we need to review the following:
To open the circuit protection device in less than one second,
the fault current returning to the source must quickly rise to approximately 6x (fast
acting fuses) to 10x (for other types of devices) the rating of the circuit overcurrent
protection device. The following demonstrates the impedance of the effective ground-fault
current path required to clear a 120 V fault.
Protection Fault Impedance
To understand how a ground rod is useless in reducing touch
voltage to a safe level, we need to know (1) what touch voltage is, (2) at what level
touch voltage is hazardous, and (3) how earth surface voltage gradients operate.
1. Touch Voltage - The IEEE definition of touch
voltage is the potential (voltage) difference between a grounded metallic structure
and a point on the earth 3 feet from the structure.
2. Hazardous Level - NFPA 70E - Standard for Electrical
Safety Requirements for Employee Workplaces, cautions that death and/or severe electric
shock can occur whenever the touch voltage exceeds 30V.
3. Surface Voltage Gradients - According to IEEE Green
Book Std 142 [4.1.1], the resistance of the soil outward from a ground rod is equal
to the sum of the series resistances of the earth shells. The shell nearest the rod has
the highest resistance and each successive shell has progressively larger areas and progressively
lower resistances. This following Table lists the % of total resistance (%R) and the Touch
Voltage (T-V) based on a 120V fault. The tables % of resistance is based on 25 feet
representing 100% of the total earth resistance for a 10-foot ground rod having a diameter
of 5/8 inches.
With the intention of providing a safer installation, some,
if not most, in the electrical industry think a ground rod can be used to reduce touch
voltage. However, the voltage gradient of the earth drops off so rapidly, a person in
contact with an energized object (at any building wiring voltage) can receive a lethal
As we can see in the above table, the approximate touch voltage
three feet from the energized electrode will be about 90V. Because the resistance of the
earth is so great, very little current (1 to 10 amperes) will return to the power supply
via the earth and the circuit overcurrent protection device will not open [250.4(A)(5)
and 250-54]. Result, energized metal parts will remain energized and the touch voltage
is at a lethal level waiting for someone to make contact with it and the earth, Figure
12 250-04A5 02 250-54 04 grounding touch potential .cdr
DANGER: Scary as it might be, this is the generally accepted
grounding practice for street lighting and traffic signaling. That is, ground the metal
parts to a ground rod and not provide a low impedance fault current path! This is one
of the reasons so many people get killed with street lighting in the United Sates and
Im sure there are thousands of energized metal poles, just waiting for someone to
make contact with them. For a case study on this subject, visit www.mikeholt.com/Newsletters/dadecounty.htm.
It is critical that metal parts of an electrical system have a low impedance fault current path (equipment grounding conductor) from the metal parts to the source in accordance with the NEC [250.4(A)(5)]. A proper low impedance fault current path (not the earth) ensures that a line-to-case fault (energized metal parts) will be cleared in less than 1 second.
Al, thank you again for helping me become a better man.
The rest of the story .. provided by Tom Baker
Ungrounded light pole likely cause in
Published 2:15 a.m. PDT Thursday, April 25, 2002
An ungrounded light pole is being eyed as the possible cause of death of a 9-year-old girl at a self-serve carwash Monday evening, a city official said Wednesday.
"It appeared the light pole was not grounded," said Gary McDowell, Sacramento's chief electrical inspector, who on Tuesday examined the light at Sofspray Car Wash at 2955 Freeport Blvd.
Victoria Quail of Sacramento was electrocuted Monday night as she played near a light standard behind the carwash while family members washed and vacuumed their car.
She may have touched the light and the conduit on the ground or the metal fence next to the light, McDowell said.
"Insulation and wires were probably destroyed or deteriorated and allowed current to flow through it. We really won't know about this wire situation until someone pulls the wire out."
Sacramento police have investigated and determined the death was accidental, said Lt. Daniel Hahn. Nobody at the carwash did anything to raise suspicion of a crime, he said. "It appears to be an unfortunate accident," he said. Initially, police thought the girl fell while climbing a fence behind the carwash, but the Coroner's Office found a mark on her chin and determined she had been electrocuted.
Family members are reeling from the shock. "Right now, I'm still putting myself together," said Wayne Quail, Victoria's father. "It's something that happened. I don't know why."
Once fire officials were told of the coroner's finding, they called police, city code enforcement and Sacramento Municipal Utility District officials to inspect the carwash Tuesday.
On Wednesday, wires were seen sticking out from the light pole's base. "We saw arcing at the base of the light pole," said Fire Capt. David Whitt.
Power to the carwash was cut at 6:10 p.m. Tuesday to ensure public safety, said Scott Thomas, a spokesman for SMUD.
Yellow tape blocked off the carwashes driveway and both ends of the carwash bays Wednesday. Flowers and a white teddy bear had been placed in front of the light fixture.
The light pole is the property owner's responsibility to maintain and repair, McDowell said. The city inspects the light when it is first installed, but unless there is a complaint the city does not inspect light poles, he added.
The carwash owner, Alvin Corsini, must now hire a contractor to repair the light fixture and have city officials inspect it before power will be restored, Whitt said. The accident caught Corsini off guard. "Everything is in top working order. I don't know how this could have happened," Corsini said Tuesday night. He was unavailable for comment Wednesday.
Mike Holts Comment: A ground rod at the light pole would not have made a difference.
Here in Las Vegas, a few years ago, a boy was electrocuted during a storm. The source was a city light pole. A friend of mine, also an electrician, was on the jury. He rigged an experiment in his sink and successfully limited current flow by providing a ground (ground rod) to an energized sink full of water. He testified against the engineer provided by the city and the boy's family won a large settlement because the pole was not bonded.
I believe that grounding the pole to the earth would have done nothing. It was a steel pole soaked by a storm and installed in concrete, also soaked with rainwater. The power source was some distance away and the earth is not a wonderful conductor so grounding a energized metal pole to the earth will only help to energize the earth and concrete around it and create a step potential which could be deadly. Distance will limit the possibility of the current finding its source through the earth and kicking a circuit breaker.
A GFIC breaker would have interrupted current flow and a properly located and protected splice would have probably prevented the pole from being energized.
In short, I agree with the liability assigned to the design of the installation, but a ground rod would not have made a bit of difference and may have even increased the danger by providing a better path for the current to energize the ground around it.
Mike Holts Comment: I dont (yet) know or understand what happens to touch and/or step voltage when a metal pole is energized and its grounded to the earth with a ground rod, without an equipment grounding conductor. But you can be sure, that when its raining, the installation is not safe from electric shock/death.
Mike Holts Comment: If you have any comments or feedback, please let me know, Mike@MikeHolt.com
Copyright © 2003 Mike Holt Enterprises,Inc.