Methods and apparatus for determining that all conductors of an Ethernet connection are connected to the same powered device (PD). In one disclosed embodiment, it is first determined that a signal conductor pair of the Ethernet connection is coupled to a valid PD according to a discovery process, and the unused conductor pair of the Ethernet connection is also coupled to a valid PD. However, it is not yet determined whether they are both coupled to the same PD. This disclosure provides for injecting a polluting signal into one of the conductor pairs, and performing the discovery process on the other conductor pair. If the discovery process fails on the other conductor pair as a result of the polluting signal, then it is determined that both of the conductor pairs are indeed coupled to same PD.