Thursday, February 19, 2009

An Eruv-Checking Technological Innovation at the Allentown Eruv

[For reference, to explain Eruv in over-simplified but functional terms: An Eruv is a series of walls, punctuated with doorways, which surround a geographic area as part of converting it into a unified "enclosure" in halachic eyes.

This is important because Jewish law prohibits transporting property through an unenclosed area, or from an enclosed area into an unenclosed area or vice-versa, on Shabbat.

Each of those doorways is composed of two vertical posts, called lechis, which meet a horizontal korah that runs over the tops of the lechis.

Often, a lechi is a post placed against a telephone pole or power company pole, and it runs up to meet a korah wire that runs across the top.

Sometimes a korah wire runs into a telephone/power pole itself, and in such cases, depending on certain technical details, the pole may serve as the lechi. That is called a tachuv.]

I am proud to present the culmination of a project I've been developing with our local Eruv checkers, to develop a new tool for Eruv-Checking.

Here in Allentown, we have what I consider a very good Eruv Checking system. Almost all of our lechis run all the way up to the korah, with one notable exception that stops a few feet short. We check it every week, and we handle developing problems as they come up.

Nonetheless, in my eight years of checking the Allentown Eruv I have found a few on-going problems:

1) Training new checkers properly, with good materials and sufficient time to review each pole and ensure that they understand how it fits into the Eruv;

2) Ensuring that all checkers are looking at the same poles (where the pole does not have a lechi or company number, and is therefore harder to identify);

3) Allowing checkers to compare what they are seeing today with the way the pole has historically appeared, in order to detect deterioriation.

In order to help address those three problems, we have created a Google Map marked with each pole, with:
a) a brief description of the type of connection at each pole;

b) a brief description of any historical problems with each pole;

c) photographs of the pole, with close-up pictures of the Tachuv-pole connection or Lechi-wire connection at each pole.

The map has already proven helpful; we discovered that one pole no longer needed its lechi but was actually tachuv.

It should also prove useful on two additional levels:
1) Allowing more of the community to become intimately eruv-aware, so that they will be able to let us know if they see any problems, and

2) Enabling eruv checkers to modify this shared database, entering any issues they have encountered with specific poles.

You can find the Allentown Eruv map on-line either by:
*Going to and entering "Allentown Eruv", or

*Just clicking here.

Please take a look and let me know what you think!


  1. aha! But won't this make it easier for mischief-makers to disrupt the eruv around Purim? ;)

  2. Shorty-

    Anyone foolish enough to mess with our eruv will find out that we take protecting our eruv pretty seriously in these parts...

  3. The Kew Garden heights eruv went down one shabbos in January, but someone somehow has some video feed and saw that it was down, so they announced in (at least one) Shul that it was down so many men ran home to tell their wives not to come with the kids. The janitor had to push many strollers that day (from kids who were already at shul when the news came in).