The thin, black line snakes across the St. Louis Park sky, so nondescript it almost disappears. In some places, it's an electric power line. In others, it's just polypropylene twine, attached to a combination of utility poles and mature trees.

But its purpose has nothing to do with electricity. It's part of an eruv, a boundary around the area's Orthodox Jewish community that allows its members to do certain activities, such as carrying things, normally prohibited by Jewish law on the Sabbath.

Now in its 26th year, the 1-mile-square eruv (pronounced AY-roov) makes life more convenient for the 300 Orthodox Jewish families clustered southwest of Cedar Lake, contributing to the growth of one of the few Orthodox Jewish neighborhoods in the Twin Cities.

"For an observant Jewish family [looking to move], one of the first items on their checklist is, is there an eruv here?" said Allan Baumgarten, president of Eruv Minnesota, the corporation that built the eruv. "It's become the norm that Jewish communities of almost any size … have a community eruv."

The eruv requires weekly inspections by a rabbi, and if it's in disrepair, the observant can't carry things outside the home on Friday night or Saturday, even babies, beverages or books, until it's fixed.

But for all its significance to some, many locals don't know it's there or what it means.

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Polyurethane wire, which makes up the 1-mile-square eruv in St. Louis Park, is visibly attached to a tree in Twin Lake Park.

"It's just not that well-known," said Ann Marie Lesch, a 22-year area resident who learned about the eruv just last year.

It has come to have another purpose, said Alexander Davis, a rabbi at Beth El Synagogue: "What I see it contributing is, it defines and sets the Jewish community."

Most of Beth El's congregants, who aren't Orthodox, don't observe the eruv. Nonetheless, Beth El supported its construction, allowing the synagogue to be part of the eruv's "wall," Baumgarten said.

Through the creation of a symbolic, continuous wall around a neighborhood, the boundaries of each family's household are extended to the entire eruv, making tasks like pushing strollers, carrying keys or bringing food to a neighbor's house possible outside the home under Jewish law.

Eruvs exist throughout the United States. New York state has about 50, and there's one in St. Paul's Highland Park neighborhood.

The St. Louis Park eruv went up in 1990, Baumgarten said. The group paid Xcel Energy about $15,000, raised through community donations, to attach a durable wire to posts and trees where there's no power line.

Today, maintaining the eruv is serious business. Each week, local Rabbi Shimon Perez makes the rounds, driving or walking the four-mile perimeter. If he — or anyone — notices a problem with the wire or a utility pole, Xcel must be called to fix it. If it can't be fixed by Friday, observant residents must operate as if no eruv is in place.

There's even a hot line to call to make sure the eruv is intact, he said.

Tzipi Weinberg, whose Orthodox Jewish family owns Prime Deli, chose her restaurant's location because it was in the eruv, where there's a high concentration of people who want her product, she said.

It's mostly people who use the eruv that know about it, she said, since it doesn't affect anyone else.

"This is something we do, and we raise our children to do it," she said. "For us, it makes sense."

Erin Adler • 952-746-3283