Raritan requires a ferrite core to be installed 1.5-3″ from the end of Ethernet patch cables attached to their PDUs if your using on of their external sensor assemblies. I can’t believe that this is to suppress noise from entering into the PDU since PDUs are basically attached to a  giant antenna. The only reason I can come up for this is to reduce cross talk between the Ethernet and sensor wires before they attach to the PDU as their ports are adjacent on the chassis.  Does anyone have a better explanation?