Eruv Glossary
Term Meaning
Lechi Strip used to represent a doorpost. Can be made of anything solid from a length of twine to a 2x4 or I-beam. In the Boston Eruv, lechis are usually made of black plastic U-guard, of the type employed by the telephone company for protecting ground wires coming down the side of a utility pole. The lechis are affixed to the pole using U-shaped nails. The lechi is attached to a utility pole side starting at the ground and continuing upwards until just beneath whichever cable is being used as the vertical member of the Tzurat HaPesach (see below).
Tefach A measure equal to one "handbreadth." The Tefach is used in two general instances. One for the minimal length of a lechi (at least 10 Tefachim) and the second for the maximum distance that the bottom lechi can physically be from the ground (3 Tefachim). For the Boston Eruv, the modern equivalent of a Tefach is 4.2 inches.
Kinyan Kesef Required document to obtain permission/rights to the area contained within the Eruv. This must be obtained from all executive powers (towns, state, etc.). For an example, see a Kinyan Kesef example.
Korah The lintel portion of the Tzurat HaPesah (see below). This horizontal member can be an existing physical structure such as an existing utility (phone or cable, usually phone) cable that is already in place between a set of two poles. If no cables are located where the two Eruv poles are being used (for example along the Massachusetts Turnpike where the Eruv erected standalone poles), a length of plastic (polypropylene) baling twine is stretched between the tops of the two poles. The twine is insensitive to moisture and cold and only mildly sensitive to sun, i.e. ultraviolet radiation exposure. It holds little moisture and does not tend to build up ice during the winter. It does suffer from abrasion damage if tree branches rub against it. However, since it is electrically non-conductive, the various granting agencies allow the Eruv to use it.
Tzurat HaPesach A doorway opening. The construction of two doorposts and an overhead lintel. This construction is used when the Eruv fence or border is open and some way must be found to maintain perimeter continuity. In one case, two poles can be erected at the edges of the gap and a length of non-conducting twine is stretched carefully between the two pole tops. It is critical that the twine be attached to the pole over the absolute top of the pole and not to the pole side. If the latter method is used, the Tzurat HaPesach is invalid. An example of the Tzurat HaPesach construction used along a section of the Trolley Track section of the Eruv is shown in the Figure.
Sources of Materials
  • Twine: Black polypropylene twine, 3 mm diameter, commonly used in hay baling can be procured in 9,000 foot cartons from PolyExcel, Inc. in Clearfield, UT. Their telephone number is 801-728-3888. They are on the web and are very helpful. We use type 9000/130 (the 130 refers to the breaking strength of the twine).
  • Lechi: Black, half-inch, U-Guard can be ordered from Alpha Plastics, a division of FramTrak Industries in Middlesex, NJ. Their telephone number is 732-424-8400 and they are on the web. We purchase sets of 125 8-foot lengths (1000 feet).
  • J-nails: We purchase T-5 (half-inch) straps for affixing the lechi to a wooden pole from Briscon. They can be purchased from an electrical/plumbing supply house. They are available in units of 100 straps or a carton of 2000. You can find Briscon on the web.