Siman 395

It is a mitzvah to seek out shitufi mevo'ot just as one seeks out eruvei chatzerot, so that they do not stumble into a prohibition of carrying on Shabbat in the mavoi. And one collects bread or another item from every homeowner in the mavoi, or he grants them merit from his own through another person, and that other person lifts it a handbreadth and acquires it on behalf of all the residents of the mavoi. And he recites the blessing "Who has sanctified us... regarding the mitzvah of eruv." And even though we call this 'shituf'—this is to distinguish between it and eruvei chatzerot, as written at the beginning of siman 386. However, the essence of the name is 'eruv'—for it mixes all the residents of the mavoi to dwell in one place. And he says: "By means of this eruv, it shall be permitted for us and for all the residents of the mavoi to take out and to bring in from the courtyards to the mavoi, and from the mavoi to the courtyards and to the houses, and from the houses to the courtyards and to the mavoi." And it is necessary to mention 'houses', because we rely on shituf in place of eruv. And all the more so for us, as we only place one eruv for the entire city. And it appears to me that for us, it is necessary to say 'from houses to courtyards and to the streets and to the marketplaces, and from them to the courtyards and to the houses, for us and for all who dwell in this city.'

And when does one recite the blessing? The Tur and the Shulchan Aruch wrote: at the time he collects from the residents of the alleyway, or if one person grants them merit—he blesses at the time of the granting of merit. That is to say, and not before, but afterward—he may bless. And we have a general rule that the blessings are not indispensable; therefore, if they collected for the sake of an eruv and forgot and did not bless over it—the blessing is not indispensable. And it appears to me that the statement "With this eruv" is indispensable, for if not so, from where is it recognizable that this is an eruv? However, according to our custom, where the shamash makes the eruv by the command of the community and grants merit to all the residents of the city, and places the eruv in the synagogue, which is a great recognition that this is an eruv—then even the statement "With this" is not indispensable. (The Levush wrote that their custom was to collect flour from every house, and the shamash would bake from it for the eruv and eat the rest—it is not an eruv if they forgot to bless, since there is no granting of merit here and not everyone's portion entered into the eruv. And the Taz disputed him, because each one gives the small amount of flour so that the entire community will merit in it; see there.)