STP: Shielded Twisted Pair Cable
Shielded Cable
A shielded cable is an electrical cable of one or more insulated conductors enclosed by a shield that may be composed of braided strands of copper (or other metal), a non-braided spiral winding of copper, or a layer of metal tape. Usually, this shield is covered with another layer of inexpensive insulation. The shield acts as a Faraday cage to prevent electrical noise from affecting the signals, and to prevent electromagnetic radiation that may interfere with other devices.
In single conductor cables the shield usually acts as the return path for the signal and is usually connected to the circuit reference point. In multi conductor cables the shield will be grounded, often only at one end, and doesn't carry circuit current.
High voltage power cables shields balance the stress on their electrical insulation and are earthed to pass any fault current back to the source. Termination of the HV shields during cable installation is of great importance to prevent hazards while miminizing undesired electrical signals or currents.