Why Use Shielded Cables?
Applications where cable assemblies are used can be electrically noisy environments. Understanding the environment in which your assembly will be used in may determine whether or not your application will require shielded cables.
Electrical Noise in Cable Assemblies
Electrical noise can be either radiated noise or electromagnetic interference (EMI). In noisy environments, a cable assembly has the potential of being a main source of transfer for EMI, both as the source and as a receiver. A cable assembly can produce noise and pass it along to other equipment or act as an antenna to radiate noise. A cable assembly can also be a receiver and pickup EMI generated from other sources. When a cable assembly receives or generates noise it can seriously disrupt the function of equipment and electronic components around it, or seriously disrupt the transmission of data within itself.
Outer Sheath or Jackets
Cables used in an assembly are typically designed with an outer sheath or jacket which protects each cable from scrapes and abrasions, and also environmentally protected from moisture and spills. Outer sheaths however, are transparent to electromagnetic energy and provide no protection from EMI.
The most effective method used to resolve EMI issues in cable assemblies is cable shielding. A cable shield surrounds the components within the cable and will impact EMI in two ways. The first way the shield impacts EMI is by reflecting the energy. The second impact is that the cable shield picks up noise and conducts or transmits it to ground. In either instance the EMI is stopped from reaching the inner components of the cable. Some energy will pass through the shielding, but the energy that does pass through is so highly attenuated it will have zero impact on the assembly.
In summary, a cable assembly needs to have the proper shielding based on the application it will be used in. A shielded cable, however, will not be effective if the equipment it is installed on is not properly grounded. The connector and the cable shielding effectiveness must match.