As the nation's power demands have increased over the past few decades, the nature of the hazards posed by overhead transmission and distribution lines has become increasingly complex. And for operators of mobile construction equipment like boom trucks, aerial lifts, and mini cranes working on, near, or in the right-of-way of these overhead lines, there still seems to be a lot of confusion — especially when it comes to properly grounding this equipment to prevent electrocution. Because carrying out this task correctly can mean the difference between life and death, electrical contractors and linemen must consistently follow certain safety procedures, but part of the confusion surrounds the search for a preferred method.
Best practices “There really isn't any industry-accepted method of grounding [mobile construction equipment] that says this man will be safe all the time,” says Brian Erga, grounding expert and president of Bellingham, Wash.-based electrical safety and training company, ESCI.
However, research conducted by Erga in the early '90s suggests a method that will work most of the time — at least when it comes to equipment near distribution lines. Erga is the author of a 1991 report known as IEEE 91 SM 312-9 PWRD or “Test Results of Grounding Uninsulated Aerial Lift Vehicles Near Energized Distribution Lines.” His report concludes that equipment grounded to the common neutral (system neutral) provides the greatest level of protection for equipment operators near energized distribution lines.
While grounding to the system neutral is much more effective than using a temporary ground rod, Erga's pioneer study also pointed out the limitations of this method. In his study, by grounding the aerial lift to the system neutral, he was able to get the voltage to drop from around 6,000V down to about 200V.
“Unfortunately, in the industry we say that somewhere between 50V and 100V could still be lethal,” he says. “So we were able to lower the voltage significantly down to 200V, but we were not able to get to the point where the industry says it's now safe in all cases.”
Nevertheless, Erga's study concluded that this practice was adequate in safeguarding the worker if personal protective tools, such as rubber gloves or boots, are used. He also recommended using insulated booms and/or conductor cover-ups.
Now, more than a decade later, Erga's study still serves as a benchmark for the industry; however, many feel continued research is necessary.
Confirming conclusions A new study sponsored by Bethesda, Md.-based Electri International — a research and training organization partnered with the National Electrical Contractors Association (NECA) — has not only confirmed Erga's findings, but is also working to develop national standards for protecting linemen, groundmen, and equipment operators on the ground from primary shock during overhead line construction and maintenance operations.
The goal of the Electri study, led by University of Kansas Professor Thomas Glavanich, is to provide a National Electrical Installation Standard (NEIS) that will also have the approval of the American National Standards Institute (ANSI) for laying out jobsites and protecting workers on the ground.
“There are already techniques used to try and protect people and equipment on the ground, but they don't seem to be effective as evidenced by the number of accidents, fatalities, and injuries we're having among those ground workers,” says Brooke Stauffer, executive director of standards and safety for NECA. “The reason we're doing a research project is because we think there are serious safety concerns out there.”
The joint research project is currently in the testing phase — Phase II of its three-phase project. Although results have not yet been released to the public, Electri's projects and public relations director, Bita A. Silverman, says that preliminary testing has confirmed some key findings of Erga's study conducted more than 15 years ago.
“When available, bonding to a distribution line neutral would be better than a temporary ground rod for a contact fault,” Silverman says. “The impedance is much lower, and the path of least resistance would be the neutral conductor. As a result, current flow into the earth and the resultant step, touch, and transfer touch voltages would be minimized.”
Filling in the missing pieces While confirming results of previous studies is revealing, Electri plans on taking its study much further — primarily because the group says a lot has changed since the early 1990s.
Bill Mattiford, director of safety for Blue Bell, Pa.-based electrical contractor Henkels & McCoy, agrees. “There are changes to how we do things primarily because of the higher current capacity and multiple lines within right-of-ways,” he says.
Additionally, Silverman says, “Today, line crews are faced with higher transmission voltages, higher load currents, higher fault currents, more congested right-of-ways (including multi-circuit transmission corridors and underbuild on existing structures), higher time-current protective device settings, and increasingly restrictive shutdown policies.”
In fact, transmission line issues were not even covered in Erga's research. His results apply strictly to distribution lines. “When you get to transmission, then it's a whole different world,” Erga says. “You get much higher voltages, and you're out there where there is not a neutral. In that case, probably the best place to go is to the tower or the footing of the transmission line.”
Electri's study will look into the different safety practices needed for dealing with transmission and distribution lines. Electri also notes that different safety practices may be necessary in different parts of the country. This is due to some evidence suggesting that varying climates and soil conditions can affect safety at a given work site.
“Where we did the test [for IEEE 91 SM 312-9 PWRD] was out in Centralia, Mo., at AB Chance Co., where the ground resistance is very, very low,” Erga explains. “It was 18 ohms ground resistance. I'm in Las Vegas, where the ground resistance is 2,000 ohms or 3,000 ohms. I could probably stand here and touch a truck that's energized at 500V and walk away and not even feel it. Since it's so dry here, the ground is going to give you a high resistance. So depending on where you are in the country, grounding the vehicle to the system neutral may give you perfect protection, but we can't say that across the whole United States in every single case, unfortunately.”
Man cannot live by grounding alone Other varying factors that the Electri study will explore include different methods used to isolate and insolate mobile construction equipment across the nation, as well as other safety techniques used in addition to grounding.
“Grounding isn't a full answer,” says David MacCollum, chairman of the board of governors for Sierra Vista, Ariz.-based Hazard Information Foundation Incorporated (HIFI). “I'm not against grounding, but I also know that grounding doesn't always work.”
In Erga's 1991 study, he learned that even insulated work boots can make a big difference in protecting workers, when combined with grounding the mobile construction equipment to the system neutral. “In one of our tests, I took one of my lineman's boots off, and we laid the boots on the ground, putting the steel plate on top of that,” he says. “We found with the plate on leather boots, we had no voltage whatsoever, so even the leather boots insulated it from that 200V.”
Of course, this is assuming that the vehicle is allowed to ground to the system neutral. “We're talking strictly utility workers that have the ability to get to the system neutral,” Erga says, adding that, for non-utility vehicles that must get close to the lines in order to perform their work, “We may send someone from the utility over there to be an observer or a safety watch and watch them. We may do some specific grounding, but that's a very rare case.”
For those vehicles that can't ground to the neutral, Erga says they are required to keep their vehicles at least 10 feet away from overhead lines. MacCollum recommends the use of modern technologies to meet this requirement. “Your tools that are available are very helpful,” MacCollum says. “There are proximity alarms that work, there are insulated links that help, and there are range limiting devices, which program an envelope that the boom can move in when they're working close to a power line.”
Because results from the Electri research project are not expected for at least another year, linemen and electrical contractors operating mobile construction equipment will have to rely on current work practices and studies from the past.
Until then Mattiford says he looks to guidelines such as IEEE 524, various ASTM standards, and OSHA 1910.269 when considering the safety precautions Henkels & McCoy employees should take with mobile construction equipment near overhead power lines. Also, OSHA's 1926 Subpart V covers standards for construction of electric power transmission and distribution lines.
However, Mattiford notes that OSHA regulations are really more performance standards, as opposed to a step-by-step guide of how something should be done. “They give you sort of like the end game — here's where we'd like you to be, and we know there are multiple ways of getting here,” he says.
For now, Erga says, “It's either ground to the neutral or totally insulate or isolate the truck. And I know more utilities are going to what they call a cradle-to-cradle rule where they require the truck to be grounded before the boom comes off the cradle — it stays grounded until it gets back into the cradle — and then take other precautions.”
Sidebar: Tips for Working Near Overhead Power Lines
The following tips come from a December 27, 2005 report produced by the Washington State Fatality Assessment & Control Evaluation (FACE) Program.
Employee and supervisor training Employers should ensure that their employees and supervisors are trained to recognize the hazards of working near overhead power lines and how to use proper procedures to eliminate or minimize these hazards. Supervisors and employees should know the location of all overhead power lines before starting work. Check the height of your vehicle's load and the height of the power lines before you go under.
Safe distances Maintain safe working distances from all overhead wires and power transmission lines. When operating mechanized equipment, make sure that the equipment or material being moved is at least 10 feet away from power lines. Voltage levels over 50kV require distances greater than 10 feet.
De-energize or insulate Contact utility company or owner of overhead power lines prior to the start of work to de-energize and ground the lines or install insulation, if feasible. Work closely with the utility company throughout the project to eliminate or minimize the risk of contact with energized power lines.
Spotter A trained, qualified worker should be assigned to observe the clearance of equipment operating near power lines when it is difficult for the operator to judge and maintain the required distance.
Warning devices Electronic warning devices installed on cranes or other equipment can be used to alert the operator if the boom is coming too close to an energized line.
Sidebar: Grounding to the System Neutral
Following are the conclusions of a 1991 study by Brian Erga, IEEE 91 SM 312-9 PWRD, also known as “Test Results of Grounding Uninsulated Aerial Lift Vehicles Near Energized Distribution Lines.” This study primarily addressed aerial lift vehicles with uninsulated booms and was conducted using a 1969 Ford C-600 Cab-over digger-derrick line truck.
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Tests showed that contacting an ungrounded aerial lift vehicle at the same moment it contacts an energized distribution line can be fatal to unprotected workers.
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No protection was provided to the worker with the vehicle grounded to a temporary ground rod.
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Nearly maximum fault current was generated when the truck was grounded to the common neutral or pole ground, allowing for very short clearing time and lower body current.
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The electrical flash and smoke created at the contact point of the truck's boom could produce electrical flash injury for workers within several feet of the contact point.
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If vehicle grounding is used, this report recommends that additional safety equipment be used, including insulated booms and/or conductor cover-ups, as well as vehicle barriers or personal protective tools, including rubber gloves or boots.
