Stray voltage: The silent killer
November 26, 2018 - One winter morning in early 2004, PhD student Jodie Lane was walking her dogs through the slushy sidewalks of New York City when all of a sudden, without any warning, both she and her dogs were writhing in pain, hit by an invisible force. A metal sidewalk plate had become energized at 57 V, due to the corrosion and insulation failure of an antiquated and poorly maintained wiring system beneath it.
Passersby attempted to help Jodie, but they got shocked. Two local foot-patrol officers were quickly called to the scene, but after one of them was shocked too, the other cordoned off the area with yellow ‘do not cross’ caution tape.
Staff from a local store raced over in rubber gloves and with wooden mop handles in an attempt to push Jodie away from the metal plate, but first responders blocked them from helping and even threatened to arrest them.
It took more than 20 minutes for Jodie to die. Onlookers continued to plead frantically with the first responders to help her in her final moments, but all they would do was watch the tragedy unfold, safely from behind the yellow tape. Eventually, an electrical utility crew showed up and turned off the power, so an ambulance crew could remove Jodie’s body.
Jodie’s father, Roger, successfully sued the utility for $7.2 million and used the money to set up an education fund at her university and a public safety foundation in her name. One of the conditions of the settlement was that the utility had to make public a city map detailing all stray voltage locations. In this process, more than 34,000 locations were uncovered across the city!
The electrical and political problems uncovered in New York are not unique; they are also occurring in other major cities across North America with aging infrastructure, including Vancouver, Toronto and Montreal, where dogs have been killed or injured by electrified sidewalk plates.
Yet, these street shocks are still often referred to as ‘freak accidents’ or ‘isolated incidents.’ This has allowed municipal governments to dismiss the existence of stray contact voltage in their cities.
To combat the problem, private electrical testing companies have emerged that use high-tech equipment to scan pedestrian-accessible areas and correct any stray voltage conditions they find. Some utilities are asking for this testing to be performed at least twice a year.
How it happens
Stray voltage occurs when an electrical current moves from flowing within an electrical wiring system to another conductive object, such as a metallized water piping system, a steel structure or a concrete floor, and then through a person or animal who comes into contact with it.
By way of example, a bus shelter with electrically powered billboard advertising on the side was found to be energized with 120 V throughout its steel structure. Shortly after it was tested, the utility dug up its feeder and fixed the incorrectly wired installation.
Dangerous when wet
Marinas and swimming pools are also prone to stray voltage issues. One yacht club’s marina was tested to find more than 15 A of stray current flowing in the water between the boats; it takes less than 0.1 A to stop your heart! Concerned more with liability than with fixing the problem, the club’s directors simply installed ‘no swimming’ signs.
When professional engineers closed a community swimming pool where children had received electrical shocks, the mayor attempted to reopen it prematurely for a scheduled swim meet. Some politicians do not understand how life-threatening stray voltage can be!
More recently, a new water park was built directly beneath a 27,000-V electrical distribution feeder. With a high-voltage electrical pole mounted within a few feet of the water’s edge, it appeared to be an accident waiting to happen, though it was apparently built to current electrical codes.
Faulty concentric neutrals on high-voltage underground cables created stray voltage in a U.S. lake, resulting in death for one swimmer and brain injuries for two others. The electrical utility was successfully sued in civil court, but refused to fix the problem, leaving cottage owners unable to sell their properties after the highly publicized event. A similar stray voltage situation also shocked a young swimmer in a lake in Southern Ontario.
Shutting down farms
While dogs on sidewalks and swimmers in cottage country have made headlines, cattle on farms have been dying from the effects of stray current and voltage for at least the past 40 years. Indeed, thousands of cattle have been adversely affected.
Dairy cows are extremely sensitive to electricity. Generally, they will start to notice currents flowing through their bodies at levels between 0.001 and 0.002 A and subsequently produce less milk each day, as well as suffer additional health problems, such as mastitis. At higher levels, they may die.
In Wisconsin in 2008, a dairy farmer successfully sued an electrical utility for $2.3 million over the stray voltage issues from which his cattle had suffered for at least 20 years. He went on to publish a book outlining not only the court case, but also the surrounding electrical technical issues, for other farmers to use as a reference guide.
In some of these cases, dairy farmers sell off their remaining cows and start planting crops on the land instead. One of them, based near Woodstock, Ont., claims he has lost more than 100 cows and $1 million due to utility-based stray voltage issues that have been confirmed by electrical engineers.
In a recent investigation, a farmer spent more than $100,000 to hire five different electricians over four years to solve his stray voltage problems. He found his cows were reluctant to drink at watering troughs or enter automated milking machines. His milk production was reduced by more than 40%.
As he tearfully prepared to sell his dairy farm to cover his financial losses, however, another site investigation led to remedial work, which managed to reduce stray current at the farm from 10 to 15 A to a constant, steady-state 0 A and stray voltage at the troughs and milking machines from 2.5 V to less than 0.02 V.
His farm had experienced a wide range of deficiencies, including main incoming power supply connection issues at the electrical panels, melted neutral/ground wiring systems, electrical equipment contamination, defective lighting systems and submersible heater dielectric insulation failures. Fortunately, all of these issues originated from equipment that could easily be controlled and corrected. Any off-farm stray voltage would have to be corrected by the utility, which is generally an extremely complex, expensive, political and time-consuming process.
A monitoring and data logging system was custom designed and permanently installed at the farm, so as to instantaneously capture and record any future stray current. When wiring or equipment fails, it can be electrically isolated immediately and replaced quickly, without adversely affecting milk production.
If an electrical circuit fails on the ‘hot black side,’ it will normally trip a circuit breaker when that breaker’s fault current threshold level has been exceeded. It is important to investigate, repair and replace the circuitry as soon as the problem occurs.
At shore-power marinas, ground fault interrupters (GFIs) should be installed on all circuits, not just the low-amperage electrical feeders. Both GFIs and stray current monitoring equipment should be installed at all community swimming pools.
Going forward, regular scanning for stray voltage in electrical utility infrastructure systems will need to become mandatory and be strictly enforced by independent policing agencies. And if a problem is found, it should be quickly corrected by the utility before anyone else suffers from it.
The utilities should examine alternative electrical distribution designs. SaskPower, it should be noted, appears to be the first in Canada to require a four-wire service drop for new residential and agricultural customers, which is a step in the right direction. Further, SaskPower recommends the installation of a bond wire between agricultural buildings to establish an equipotential plane, with the neutral bonded only to ground at the transformer or weatherhead, to prevent the ground or bond wire from carrying any current. In California, meanwhile, special electrical utility high-voltage systems designed for farming areas have yielded the ‘happy dairy cow’ designation.
Electrical failures on the grounded or neutral side of a standard system can generate extremely high levels of stray current. Indeed, the equipment may work perfectly, leaving the problem undetected for years until something abnormal happens.
A recently investigated hospital room, for example, had more than 30 A of stray current flowing through it for at least 15 years. A portion of that current would have affected every patient who was operated on within the room!
The costs to society
As illustrated in such examples, stray voltage can sneak into many areas. Electrical equipment will corrode over time and, particularly with outdoor exposure, can fail.
Recommendations for fixing such problems will cost money, raising issues of politics, shareholder returns and legal liability, but how much is each Jodie Lane’s life worth? How much is a child’s life worth at a lake, swimming pool or water park? What is the cost to society when farms are shut down?
It would appear we are now moving in the right direction, but at a snail’s pace. I believe we may still be facing some of the same types of stray current and voltage issues for the next 40 years or more.
Patrick J. Lynch, P.Eng., has been president of Power Line Systems Engineering since 1986. He graduated from the University of Waterloo in electrical engineering in 1975 and has successfully directed Power Line’s completion of more than 1,100 complex site disturbance investigations around the world. For more information, visit www.powerlinesystems.ca.
This article originally appeared in the October 2018 issue of Electrical Business.
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