Shielded Twisted Pair

What Does Shielded Twisted Pair Mean?

Shielded twisted pair (STP) cable was originally designed by IBM for token ring networks that include two individual wires covered with a foil shielding, which prevents electromagnetic interference, thereby transporting data faster.


STP is similar to unshielded twisted pair (UTP); however, it contains an extra foil wrapping or copper braid jacket to help shield the cable signals from interference. STP cables are costlier when compared to UTP, but has the advantage of being capable of supporting higher transmission rates across longer distances.

Techopedia Explains Shielded Twisted Pair

The additional covering in STP cable stops electromagnetic interference from leaking out of or into the cable.

STP cables are often used in Ethernet networks, particularly fast-data-rate Ethernets. The effectiveness of the additional covering varies according to the substance used for the shielding, such as:

  • Frequency
  • Thickness
  • Type of electromagnetic noise field
  • Distance from the shield to the noise source
  • Shield discontinuity
  • Grounding practices

Some STP cablings make use of a thick copper braided shield which makes the cable thicker, heavier, and in turn much more difficult for installation as compared to the UTP cables.

The other usual STP cables, often called foil twisted-pair cables or screened twisted-pair cables, make use of just a thinner outer foil shield. These cables are thin and more affordable versus the braided STP cable; but they are very difficult to install. Except in cases where the maximum pulling tension and minimum bend radius are strictly observed, these thinner cables may be torn during the installation process.

Furthermore, STP cables have some other drawbacks. STP cables function by drawing external interference to the shield, then getting rid of it into a grounded cable. If the ground cable is not properly grounded, STP’s noise-canceling functionality can be seriously compromised.


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Margaret Rouse

Margaret Rouse is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical, business audience. Over the past twenty years her explanations have appeared on TechTarget websites and she's been cited as an authority in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine and Discovery Magazine.Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages. If you have a suggestion for a new definition or how to improve a technical explanation, please email Margaret or contact her…