Drain Wire


Definition of Drain Wire in the Network Encyclopedia.

What is Drain Wire?

Drain Wire is 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.

Drain wire
Drain Wire (red circle)

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.

Practical guidelines for effective shielding

  1. Make sure you have a cable with sufficient shielding for the application’s needs. In moderately noisy environments, a foil alone may provide adequate protection. In noisier environments, consider braids or foil-braid combinations.
  2. Use a cable suited to the application. Cables that experience repeated flexing usually use a spirally-wrapped shield rather than a braid. Avoid foil-only shielding on flex cables since continuous flexing can tear the foil.
  3. Make sure the equipment that the cable is connected is properly grounded. Use an earth ground wherever possible and check the connection between the ground point and the equipment. Eliminating noise depends on a low resistance path to ground.
  4. Most connector designs allow full 360° termination of the shield. Make sure the connector offers shielding effectiveness equal to that of the cable. For example, many common connectors are offered with metal-coated plastic, cast zinc, or aluminum backshells. Avoid both overspecifying and paying for more than you need or underspecifying and getting poor shielding performance.
  5. Ground the cable at one end. This eliminates the potential for noise inducing ground loops.

A shielded system is only as good as its weakest component. A high-quality cable is defeated by a low-quality connector. Similarly, a great connector can’t do anything to improve a poor cable.

External references:

What is Drain Wire?

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