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Wet, Wetter and Wettest

December 10, 2012

Wet, Wetter and Wettest

Q:

I have two areas under consideration for rejuvenation next year.

  • The first is a sub-division with 40 year-old cable that is in relatively dry sandy soil.
  • The second sub-division has 15-20 year-old cable that is in very wet, swampy soil.

All other things being equal, which area would enjoy the greatest benefit from rejuvenation? Is there any data to support the recommendation? I hypothesize that the cables in the swampy soils should be injected first, since those cables are constantly in water and injecting them might yield the greatest benefit.

A:
This is a really great question because the wetness of the soil at one meter depth is not often discussed and often misunderstood. Fortunately one of my colleagues wrote a paper cited below that unearths the truth of the matter.

Bertini, “Molecular Thermodynamics of Water in Direct-Buried Power Cables,” IEEE Electrical Insulation Magazine, Nov/Dec 2006.

I would encourage my readers to review that paper in its entirety as it dispels many common myths. However, I asked the author to summarize the portion of the paper that relates specifically to your query and he has done so in a YouTube video. Watch this video and learn why both populations of cable are equally wet.

In your inquiry you say, “All other things being equal.” But are they really equal? I would suggest that the first criteria should be: Which of the two areas has had the greatest reliability issues per foot of installed cable? If reliability is equal, I would use age as the next best predictor of future performance.