An uninsulated wire included in shielded cabling that runs the length of some coaxial cabling or shielded twisted-pair (STP) cabling. The drain wire makes contact with the foil sleeve or mesh along the wire.
The externally exposed portion of the drain wire should be connected to a secure ground connection. This ensures that the wire is properly grounded and that the shielding in the wire operates effectively. It also helps to maintain the two ends of the wire at the same voltage with respect to ground.
If voltage differences form between the ends of a network cable, they can lead to a sudden voltage surge or discharge that can damage attached networking devices.