Everything You Need to Know about the Shielded Cable

What is the Shielded Cable?
The shielded cable is also called the screened cable. The construction of the cable is a core (conductor), an insulator that wrapped the core, the shield layer that encloses the insulated core, and insulation that jackets the cable wire. The core is insulated by a dielectric material. The shield layer made of conductive materials (metals or conducting polymers) forms a Faraday cage. A Faraday cage contains electric noises, electromagnetic radiation, radio-frequency interferences (RFI), and other electromagnetic interferences (EMI) that affect the signals. EMI tends to occur in an environment that involves the use of high electrical power.

The type of shielded cables is determined by how the cable is shielded. Shielded cables for different applications use different materials and methods to shield the wires. Each method provides the wires with different levels of shielding. The three most common shielded cable types are foil shield, braid shield, combination shield, and spiral shield.

Spiral Shield
The spiral shield, also serve shield, allows for the greatest flexibility of the cable, which makes it more applicable than other types in instruments and portable device applications. The spiral shield is constructed with conductor strands (often copper) that wind around the insulated conductor. It is light, thin, and therefore inexpensive. Cables using a spiral shield are more bendable than other types. However, it terminates easier and is prone to high-RFI environments. It is most effective in low-frequency applications.

Braid Shield
The braided shield weaves metal conductors into a criss-cross pattern to wind around the insulated conductor. Such a construction gives a firm wrap around the core and still allows a certain level of flexibility. Like the spiral shield, the braided shield is also effective in a low-frequency environment. Moreover, it performs quite well in a high-frequency EMI environment as well. It is estimated to provide over 90% EMI shielding ability. Using the braid structure with other shield types can further improve the shielding ability.

Foil Shield
The foil shield is an extremely thin metal film usually made of aluminum. The aluminum film is coated on another flexible plastic film. It is also called metal-coated mylar. The aluminum foil provides low-frequency EMI protection. Since the metal-coated laminate is extremely thin, the foil shielded cable comes in lightweights and smaller diameters. This type of shield offers excellent EMI shielding ability but shows weak noise-shunting ability. Therefore, in some applications, the foil shield combines with other shields to better shunt the noise.

Combination Shield
The combination shield refers to the implementation of both braided shield and foil shield (sometimes more) at the same time. The aluminum foil shield as the inner layer, provides EMI protection while the braid shield, the outer layer, strengthens the structure as well as noise rejection. If you are looking for the highest shielding effectiveness, the combination shield is the best option. It not only has 100% coverage but also good physical protection. However, the use of two or more shields at a time significantly increases its cost.

Shielded cables isolate the power line and data transmission line from RFI and EMI to protect a system and keep it operating safely and properly. The environment where EMI occurs the most includes power plants, electric transmission facilities, data centers, data processing equipment, and more. In these industrial settings, it is mandatory to use the shielded cable instead of the non-shielded cable. In addition to the industrial application, airports and radio stations also use shielded cables because data processing and information exchange in these settings must remain out of interference.

How to Choose the Shield Cable?
Since each shield type offers a different level of coverage and protection to the cable, it is advisable to choose the shielded cable based on the application. For example, a low-to-moderate-noise working environment requires only a foil shield for the cable, whereas the noisier environment may require the braided shield or combination shield for enough protection. You should also put the use of the cable into consideration too. If the cable needs to be bent frequently, the spiral shield is a better option. Choosing the right shielded cable not only ensures the safe operation of your system but also a reasonable cost of installation. Contact Winfox right now if you need more information about our products and service.