When the "Gadol Ha’ir" ("leader of the city"), which nowadays would be the congregational Rabbi, prepares his Erub Tabshilin on Ereb Yom Tob, he has in mind for it to cover all members of his community. Hence, if a member of his community forgot to prepare an Erub Tabshilin, or if he remembered to prepare an Erub but it was lost before Friday afternoon, he may rely on the Rabbi’s Erub. Since the Rabbi had all members of the community in mind, members who forgot to prepare an Erub Tabshilin or whose Erub Tabshilin was lost before Friday afternoon are still covered, and they may therefore cook on Yom Tob for Shabbat.
This Halacha, however, does not apply in cases where an Erub Tabshilin was prepared incorrectly, such as if someone used rice as the cooked food item of the Erub. As noted in a previous edition of Daily Halacha, rice is not valid for the Erub Tabshilin since it is not commonly used with bread ("Le’lafet Bo Et Ha’pat"), as opposed to cooked foods like eggs or cheese (which is pasteurized). If a person used rice for his Erub, and then on Yom Tob hears the Rabbi deliver a class about Erub Tabshilin and learns that rice is not valid, he cannot assume that he is nevertheless covered by the Rabbi’s Erub. In this case, since he prepared an Erub, he implicitly established that he wishes to rely on his own Erub, rather than the Rabbi’s. Thus, he is not covered by the Rabbi’s Erub, and his Erub is invalid. (In a future edition of Daily Halacha we will, please G-d, discuss the options that are available to a person in this case.)
Summary: If a person forgot to prepare an Erub Tabshilin before Yom Tob, or if he prepared an Erub but it was lost before Friday afternoon, he may nevertheless prepare on Yom Tob for Shabbat, as he may rely on the community Rabbi’s Erub. This does not apply to one who prepared the Erub incorrectly.
