Misplaced insulator proves fatal

Article By : John Dunn

The insulator on a guy wire supporting a pole was placed above the lowest 12-kV line, leading to a catastrophic power line accident.

A ghastly story recently appeared in Microsoft News about the electrocution of one man and the terrible injuries inflicted on another man, the loss of both arms, as the result of a power line accident.

Here are a few snippets from that article, which originally appeared in the Chicago Tribune:

“… ComEd engineers testified that one of several wires connected to the pole was not properly insulated.”

“… the guy wire — the metal line that runs diagonally from the pole to the ground to provide support — was loose and made contact with a ComEd line, electrifying the portion of it below the insulator and posing a serious threat to those nearby.”

“If the guy wire had been installed according to state code and federal guidelines, an insulator would have been placed below the lowest power line to stop it from electrifying portions of the guy wire closest to the ground. Instead, the insulator had been placed above the 12-kilovolt line, allowing a deadly level of electricity into the wire …”

“In images captured by Google Street View in 2013 and frequently referenced in depositions, the insulator on one of seven guy wires supporting the pole is clearly above the lowest 12-kilovolt line.”

Trying to fully understand how this tragedy occurred, I used Google Maps and succeeded, I think, in finding a photograph of the site of the power line and the pole.

misplaced insulatorThis image shows the power pole and improperly placed insulator.

I suspect that the top-most wires carry far greater high voltage than 12 kV. It looks to me like the 12 kV wires are located about midway up the pole. Please note that one guy line’s insulator is placed high above the 12 kV wires. Its placement, as I understand from the article, led to a catastrophic accident as shown below.

misplaced insulator broken wireIf the wire above the insulator gets broken, the wire below the insulator falls onto the 12 kV line.

When a guy line was “loose,” the guy line wire below the insulator came down and made contact with a 12 kV line which brought that high voltage all the way down to street level where the two victims were hit.

A key point in the article is that this installation dates back to 1968. For 50 years, over the course of half a century, nobody ever noticed the hazard and no inspector ever flagged an issue. Then the guy line came down.

The regulatory agency responsible for utility oversight and the utility company itself look to me like they are playing “CYA” with the situation. Alarmingly, the article’s authors suggest that this kind of hazard is not unique to this location and that we should all start looking around at the utility wiring where we live and work. Heaven forbid, we might find something similar.

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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