Figure below is an old-fashioned housing building of 7 floors. The ammeters are distributed over floors. There are three ways to approach power line communication: 1. Using one bridge only in the building. It will save costs, but the connectivity to end-users will fail because of signal attenuation resulted by the too long coupling line; 2. Using two bridges in the building (see figure below). Although costs are increased, the signal will be much more stable; 3. For those housing building with mechanical ammeters, it is suggested that each unit be equipped with one PLC bridge. The injection point should be at the upstream node of the unit's power line. We can apply direct signal injection with an adaptor.