A system and method for using an Ethernet physical layer device to identify cabling topologies. A power sourcing equipment (PSE) can power independent powered devices (PDs) using two sets of wire pairs in a single four-pair cable. Higher power PSEs can power a single PD using all four wire pairs in the cable. Conventional power over Ethernet (PoE) analog techniques (i.e., voltage, current, etc.) have a difficult time distinguishing where the wire pairs are going from the PSE. By using information (e.g., negotiated speed, link energy, distance diagnostic, etc.) generated by the physical layer device (PHY) subsystem, the PoE system can determine whether the two sets of wire pairs in a cable are powering a single PD or two independent PDs.