Shielded cable is offered in a variety of wire and cable products such as shielded tray cable, shielded cat 5 cable and VFD cable. The most common reason for a shielded cable is to cut down on cross talk between conductors, neighboring cables and any other electromagnetic energy that the cable encounters. A shielded cable allows a signal that is being carried to transfer cleanly and without loss of transmission. It should be noted that some shielded cables actually have an exposed shield. This type of shielding is for mechanical protection rather than transmission purposes.
The construction of shielded cables is fairly simple. A shield is usually applied over the conductor or conductors of the cable with a jacket applied overall. The shield is composed of conductive materials so that energy cannot readily pass through and interfere with the conductors. Some shielded cables have multiple shields. Coax cable for example has up to 4 separate shields on one cable. A shielded cable with multiple pairs may have each pair shielded to protect itself from the cross talk of the individual pairs. These shielded cables also have an overall shield to protect the entire cable from outside interference.
Shielded cable is offered in foil and braid shields. The shielded cables constructed with a foil shield are wrapped in a conductive material made of aluminum or copper. The braided shield is a mesh of tiny wires that are woven around the conductors or cable. The braid is made of metals such as aluminum, copper or steel. A shielded cable comprised of a foil shield is more likely to have complete coverage however the foil is not as easy to attach to connectors. A shielded cable with a braid comes up short in that the braid cannot provide the overall coverage that foil can. When the braid is weaved into a braid there are inevitably holes. When the cable is flexed the holes will open up wider allowing more interference to the dielectrics.
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