Types of Shielding: How do They Benefit Cable Assemblies?

FACTS CHECKED BY  Jose George​

With the advancements in technology, companies have improved the rate of data sent per second. To achieve such speed, they have to use complex cable structures. However, the signals have to experience increased electrical interference failures due to such circuits. The most common types of disturbance include Radio Frequency Interference (RFI), Electrostatic Interference (ESI), and Electromagnetic Interference (EMI). Cable manufacturers think insulation alone can protect the signals from such “noise.” You require additional shielding over your wires to lessen the noise effects. There are different types of shielding available. Let us see them in detail.

Wiring Box
Wiring Box

Understanding Shielded cable

You protect it from external factors such as abrasions, moisture, and heat as you insulate the wire. However, to insulate the signals from the noise, you need shielding.

Regardless of the situation, the conductors are shielded from the noise radiation. There are two ways that the shield can affect the noise. It reflects the noise and can provide its path to the ground. A small amount of energy remains in the system, but it is so weak that it does not affect the other signals.

The shielding performance varies according to their electrical environment. In addition, the cable’s cost, diameter, flexibility, and weight all play a role in determining how much shielding is needed.

The commercial settings also use unshielded cables in some of their projects. However, the area is typically inside a controlled environment in a metal cabinet. This enclosure metal act as a barrier to protect the electronics, thus shielding the system from ambient noise.

Common Shield Materials

Since shielding is essential, you have to choose the material that best suits your implementation. Some common shield materials that the manufacturers opt for are

  1. Aluminum Foil
  2. Fiberglass
  3. Galvanized steel
  4. Stainless steel
  5. Tinned copper
  6. Bare copper
  7. Kevlar

Among these materials, copper and aluminum is the first choice of most manufacturers. Moreover, Conductive nylon tapes are also used for shielding the wires from noise. However, it is not effective as other materials.

Common Types of Cable Shielding

You can see five common types of cable shielding in the market.

Metallic Braid Shields

Braided shielding is both rigid and flexible at the same time. It is formed with groups of thin wires wound together on bobbins. A braiding machine takes these bunches of wires and woven to create a braid. In most cases, this shield can insulate most parts of the wire. 

To create an equal layer on conductive surfaces, you can use strip braids as it is beneficial even at high frequencies. Moreover, using it with other shielding forms a highly effective electromagnetic interference barrier. 

Harness manufacturers have to frequently braid and unbraid the wires to terminate the cables, which can be time-consuming. Many companies have developed tools that can do braiding work at high speed to solve the problem. Also, the tools cut the wire into preprogrammed lengths. These tools have high demand in the Military and aerospace.

Braided Shielding in a cable

Caption: Braided Shielding in a cable

Spiral Shields/Serve Shields

Today, served/spiral shielding is still in use, and its versatility is one of its primary advantages. Because it is wrapped around the conductor, the shielding is simple to unwind and terminate, but it is also susceptible to being relatively inductive. A lug or termination post, in most cases, is used to secure the shielding in place. It is frequently employed in audio-related applications.

Spiral shielding for decreased interference

Caption: Spiral shielding for decreased interference

Twisted pairs are another type of spiral shielding that Alexander Graham Bell developed and patented in 1881. This shielding is still in use today.

In twisted pairs, two insulated conductors uniformly twist each other throughout the entire length of the harness. The noise coming from the surrounding cables reduces to an absolute minimum in such structures.

Twisted pairs

Caption: Twisted pairs

Moreover, in cable, solid conductors are more common than stranded conductors. However, stranded conductors are highly flexible, so you can bend them to fit across corners. Hence, the spiral shielding uses the stranded cable rules for manufacture.

Foil Shields

Foil shields are made up of a light (0.0003 inches) metallic-coated, soft plastic film covering the insulated wire to provide protection. As the aluminum makes the foil, you have to crimp the film in different places. Moreover, people frequently use it in conjunction with a non-insulated drain cord (current diverter) within a cable. The drain cable contacts the foil, and its other end is linked to the ground, providing a grounding path to eliminate EMI transmission.

Aluminum Foil shielded cable

Caption: Aluminum Foil shielded cable

Combination shields

In combination shielding, you will use two types of shielding at once. For example, many cables have a loose braid over the foil shield for maximum protection. These cables are applicable in areas where you need frequent bending of cables during installation and maintenance.

You can also find a twisted pair cable with metallic foil in other cases. It also helps in reducing the effects of EMI on the signals.

Combination shielding featuring Braided – Foil layer

Caption: Combination shielding featuring Braided – Foil layer

Solid shields

Solid shielding is another most effective option. The metal tube is either rigid or semi-rigid in construction and made of copper or aluminum that surrounds and protects the insulated conductor. It provides complete safety against electromagnetic interference (EMI). Moreover, you may construct the larger cables from the plastic laminated tubing.

So which shield type is best?

Indeed it is a tricky question. It is because the best shielding method is the one that provides you with maximum protection from interference. For example, the signals face much resistance from the cable in lower frequency areas. In that case, braid or spiral shielding will provide you with good coverage. However, it would help to have 100 percent protection against noise in higher frequencies. In such a situation, foil shielding is your go-to option.  

It’s essential to think about how shielding will work in most cases, but you will also consider how it will affect other things. It might be hard to choose the correct shield because of flexibility, flex life, diameter, weight, and cost. Additionally, you have to ground the wire to terminate it properly. It means that the termination method can play a role in shield choice.

Moreover, you can also combine different shielding types and use them to stop noise interference. For example, putting a foil and braid on top of each other will make a shield that covers 100% of the area and has low resistance, making it good at low and high frequencies.

Practical Guidelines for Effective Shielding

Here are a few guidelines to achieve an effective shielding on your cables

  1. Ensure that you choose the right type of shielding for your intended implementation.
  2. Also, in the case of areas with more twists and turns, use spiral wrapping cables since any other type of cable will face scratches and cuts over the surface, losing its effectiveness.
  3. Check the grounding system of the wire. I prefer using the earth grounding and keeping an eye on the connection point. Moreover, eliminate resistance on the ground path so that the excess charges can flow easily.
  4. Ensure that the connectors also have proper shielding since the signals can also scatter at this point. Many connectors do offer metal, plastic, or foil coating. So, choosing the terminal that gives you better performance in application circumstances.
  5. Ground the cable only from one end. It will reduce the chances of ground loops and provide only one path to the noisy signals.

Conclusion

Shielding the cables is essential to reduce interference in the signals. Moreover, you can combine two types of shielding to give your lines 100% protection from electrostatic interference. You can use foil, braided, spiral, or solid shielding. Here at Bloom, we offer wiring harnesses and cable assemblies. Your connection is made with attention to detail.

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