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There was a recent lightning incident where fifty people were hurt while standing on wet soil at the moment of a nearby lightning strike that caused an electrical current to flow through the ground. Seven people were hospitalized but fortunately, there were no fatalities.
The incident raises a point that I have seen made as to whether overhead power lines are more prone or less prone to lightning strike damage than buried power lines.
The issue is not as simple as some would have you believe.
Consider the following image in Figure 1.
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Figure 1 An elevated power line and a lightning strike where the power line is isolated from the wet soil current. Source: John Dunn
Apart from a direct strike to the power line itself (I once saw that very thing happen but that’s a separate story), an overhead power line is pretty much isolated and protected from the wet soil’s current paths.
However, if the power line is buried, the wet soil’s current paths can impinge on the power line very much in the same the way as lightning currents impinged on those fifty people (See Figure 2).
Image may be NSFW.
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Figure 2 A buried power line and a lightning strike where the power line is subjected to the wet soil current. Source: John Dunn
It has been suggested from time to time that power line burial is a guaranteed way to protect any power line from a lightning event. That may or may not be true depending on many circumstances, but power line burial is NOT an absolute panacea, not by any means.
Soil composition, the presence or absence of nearby structures, the presence or absence of water mains, various lightning arrestor arrangements, dollar expenditures for excavation efforts, and so forth must all be assessed by experts of which I most definitely am NOT.
In the midst of many buildings—many tens of stories tall—within the borough of Manhattan, New York City, many power lines are located below ground, underneath all sorts of concrete and asphalt. In the borough of Queens, however, where I grew up (Rego Park to be precise); overhead power lines are found all over the place.
There are no simple answers and no clear-cut conclusions. Rather, this essay’s purpose is merely to dispel any simplistic thinking about the issue.
John Dunn is an electronics consultant, and a graduate of The Polytechnic Institute of Brooklyn (BSEE) and of New York University (MSEE).
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