In addition to the benefit of protection against damage to cable components from cable motion and use, proper shielding is essential to many applications as it can keep out unwanted external interference. In many applications, electromagnetic interference (EMI) is a threat to signal integrity. Shield quality is of particular importance in small signal or high frequency applications where a slight variation can have significant impact. All electrical cable will radiate energy to, and pick up energy from, its surroundings. As such, shielding can also be used to contain the electromagnetic energy radiated by a cable, which can protect nearby sensitive components.
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The three most common shield types used by New England Wire for multi-conductor cable are braid, spiral, and foil. A braided shield is made of interwoven conductive wire. A braid can be manufactured using a wide variety of materials and wire sizes and can be applied over an extensive range of cable diameters. A spiral shield is made of conductive wire helically wrapped over the core. As with a braid, a variety of materials and wire sizes can be used, however, spiral shields are generally limited to small or mid-sized cables in order to achieve high coverage. A foil shield is a metallic foil helically wrapped around the cable with overlap. A variety of foil options can be utilized, however, most common is aluminum laminated with a polyester backing. Variations or combinations of the standard types are often used to provide a custom solution to a particular application.
In addition to wire and foil based shielding options, we can also manufacture with semi-conductive tapes, coatings or extruded layers. These are typically used in conjunction with wire based shields to provide additional shielding, but more notably, they are used for low noise or corona resistant high voltage cables.
The ideal shielding method for any application depends on the specific application for which it is going to be used. For example, shielding effectiveness at low frequencies is largely influenced by resistance. Therefore, wire based shields such as spirals and braids are ideal. At high frequencies, coverage becomes the primary factor making 100% coverage foil shields the most effective option. At mid-range frequencies both resistance and coverage are influential so a high coverage braid is typically used.
While shielding effectiveness is often one of the primary concerns for most applications, other impacts of shielding should be considered. Design constraints such as flexibility, flex life, diameter, weight, and cost may influence the shield selection. Furthermore, in order to get the full benefit of shielding, the shield must be grounded properly, consequently, means of termination can play a role in shield selection.
Variations or combinations of the standard shield types are often used to maximize shielding effectiveness for a given application. For example, stacking a foil and braid will provide a shield with 100% coverage and low resistance making it effective from low to high frequencies.
Shielded cables are cables encased in a form of conductive layer. This layer is designed to shield internal conductors from electromagnetic interference, or EMI. Shielding becomes increasingly important when cable is installed near sources of high voltage or sensitive electronics. It assists with data retention while preventing EMI from leaking.
Well for Ethernet Cable you have a few options
Starting with the lowest level of shielding, UTP, this cable provides no shielding from EMI. These cables are generally more cost efficient and easier to work with, at the cost of having no form of EMI resistance.
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F/UTP, or Foil Unshielded Twisted Pair, has an internal layer of shielding that wraps around all of the twisted pairs. This shielding is just below the jacket and has a copper drain wire connected to it. The drain wire grounds electricity after the cable has been terminated, and is an essential part of all shielded cable. As seen below, there is only one layer of shielding that encases all of the conductors, however each individual twisted pair remains unshielded.
For a guide on how to terminate this cable, check out our post on Terminating RJ45 Modular Plugs!
U/FTP, or Unshielded Foil Twisted Pair, has individual foil shielding wrapped around each of the twisted pairs and is essentially the opposite of F/UTP. As shown in our image below, each pair clearly has its own foil shielding. This form of shielding provides high levels of EMI resistance, and is generally more expensive than the types of shielding listed earlier. Due to the shielding being applied to each pair individually, terminating this cable can be difficult when compared to unshielded cable.
The highest level of shielding is S/FTP, or Shielded Foil Twisted Pair. As you can see below, this cable combines the shielding of both U/FTP and F/UTP. This cable features a foil shield that encases all of the conductors, as well as individual foil shielding for each twisted pair. Like all shielded cable, this cable also requires a drain wire to ground the electricity after termination. While terminating this cable can be a harder process than terminating unshielded cable, this cable provides the highest level of EMI protection to help ensure data quality.
For Coaxial cable, there is often a higher level of shielding required when compared to ethernet cable. In fact all coaxial cable requires some form of shielding.
Braided shielding features either copper or aluminum wire tightly braided together. As picture below, this shielding is located beneath the jacket of the cable, and right above the dielectric. The purpose of this shield is not just to prevent EMI, but also to help keep the RF signal inside the cable. For Coaxial cable, the shielding helps to prevent signal degradation of large distances.
Dual shielding, features both a wire braided shield, and a solid aluminum shield. These two shields provide a higher level of shielding and help the RF signal travel further. As you can see in the cable image below, the braid of this shield is not woven as tightly as the one shown above. The cable above features a 95% braided shield, while the dual shielded cable features a 60% shield. This is because the 100% foil shield below the braid provides a high level of shielding already, so a tightly woven braided shield is not necessary.
Quad shielding takes a wire braided shield and solid aluminum shield and doubles it. Once again you can see below, that the braid of this shield is not woven as tightly as the braided shield in the first coaxial cable. In fact, the first braid of this shield is a 60% shield, and the second is only a 40% braid. Still, this level of shielding is dramatically higher than that of the cables before it, as the two layers of 100% foil shielding make up the difference.