Contrary to popular belief, stray voltages are not lethal, according to Jim Burke, executive consultant at electrical consulting firm Synergetic Design, Raleigh, N.C. Though state officials and certain media have blamed stray voltages for a recent string of pedestrian and canine electrocutions on New York City streets, Burke says this is impossible, based on the traditional definition of stray voltages.
“Stray voltage is basically caused by the normal operation of a utility system,” Burke says. “You have what we call an unbalanced current. When the current comes back to the neutral, that creates a voltage. That voltage, which can be transferred into the home or any place, is generally less than 8V or 10V. If you have something sensitive like a cow and a milking machine, that's an issue, but if it's just me touching it, it's not going to kill me.”
The actual culprit in these recent cityscape electrocutions is what Burke calls “contact voltage.” Contact voltage has occurred on city streets when energized wires accidentally came in contact with manholes, metal sidewalk plates, light poles, and service boxes.
Though the steps being taken to prevent these kinds of electrocutions — such as using more durable dual-jacket rubber cables, installing isolation transformers, and coating streetlights with nonconductive insulating paint — may accomplish that goal, Burke says confusion about the difference between stray and contact voltages has led to the passage of laws that attempt to enforce impossible standards. In some states, for example, laws are being passed requiring stray voltages to be less than 5V. In Wisconsin, Burke says utilities must keep stray voltages below 0.5V.
“If you're going to barricade everything that has 3V or 4V on it, you really have to barricade batteries from drug stores,” Burke says, noting that OSHA standards say it takes 50V or more to be lethal — far above the stray voltage range.
“You have a lack of expertise out there, which is really a problem these days,” Burke explains. “All of a sudden the lawyers take over, and now they've redefined stray voltages. Now, to the media, and maybe to the masses, it's all one thing.”
Burke has worked with the IEEE Stray Voltage Group on developing a white paper with clear definitions of stray voltages and contact voltages, but he says it may be a few years before anything is officially released. “I don't know how they'll end up labeling this thing, but just so people know that there are two different conditions they're mixing up,” Burke says. “What may happen here is we'll have to come up with a brand new term that can't be confused.”