94:24 In many communities, they combine all the roads and streets with an eiruv in the shape of a series of doorways and they rent the property from the secular authorities so that they can carry all throughout the city. This must be carried out through a rabbi who is an expert in this area. In these communities, it is customary to place the eiruv in the shul because it is community property and it need not be a residence.
94:25 In a place where the community has not set up a general eiruv but residents whose homes are in the synagogue courtyard make an eiruv, they may not place it in the shul. In this case, it must be placed in a residence. (If they do place it in the shul, it doesn't work - Mishnah Brurah 365:40.)