Lavud – Eruvin16b
(excerpted from The Contemporary Eruv)
Overhead cables often weave back and forth. One of the most relevant question concerns the following case: Three utility poles, each consisting of an upright pole and a crossbar across the top, stand in a row. The overhead cable runs directly across the first and third pole in the row, but is connected to the crossbar of the middle pole. Here, even when at rest, the cable does not run directly from lechi to lechi.
Rabbi Meir Arik (Imrei Yosher 2:133. See also Yesodei Yeshurun, ibid., pp. 282-283) submits that a lenient approach may be in order if the cable is within three tefachim of a hypothetical straight line. He explores the possible application here of the halachic mechanism of “lavud” (literally: “connected”). Halachically, two objects within three tefachim of each other are considered connected. Here, we would view the cable as "connected," i.e., repositioned, to its proper hypothetical straight line. Questions, however, may be raised concerning this approach. Rabbi Aryeh Pomeranchek (Emek Bracha, Sukkah, siman 18) identifies only two classifications of lavud, neither of which are applicable to our case. One type of lavud allows us to regard any object within three tefachim of another object as if it were connected to that other object; the other type of lavud – the type employed here, Eruvin 16b) allows us to regard the space between two objects as closed and/or blocked. Lavud does not allow us to reposition an object to a place within three tefachim of its actual location, which would be necessary to correct this problem.