969. An Eiruv That Is Lost or Destroyed

Eiruvin 6:11

Whenever a person makes an eiruv techumin, he is given a four-cubit (approx. six-foot) perimeter around the eiruv. Therefore, if a person puts his eiruv at the end of the Shabbos boundary and it subsequently rolls two cubits beyond that boundary, the eiruv is still valid because it is not considered to have left its place. However, if the eiruv rolls farther than two cubits, it ceases to be valid because it is outside the Shabbos boundary and, as we have stated, an eiruv outside the Shabbos boundary is invalid because its owner is unable to access it.

Eiruvin 6:12

If an eiruv rolled more than two cubits beyond the Shabbos boundary, or if it got lost or burned up, or if it contained terumah and was rendered ritually unclean, in all of these cases, if the mishap occurred before Shabbos began, the eiruv is invalid. If it occurred after Shabbos had already started, it is valid because an eiruv takes effect during twilight. If there is a doubt as to when the mishap occurred, the eiruv remains valid because when there is a doubt as to the validity of an eiruv, we rule leniently. Therefore, if an eiruv was eaten during twilight period, it is effective.