Shielded cables are used to minimize Electromagnetic interference (EMI) and radio frequency interference (RFI) from external electronic devices such as computers, power lines, cellular networks, air conditioners, and fluorescent lighting. EMI is unwanted signals from a neighboring transmission circuit. Shielded cables help prevent the transmitted data from EMI and cross-talk between close cable pairs and unintended coupling. This results in fewer data errors and an increase in transmission speed.
Why should you use Shielded Cable?
If your home or office is located near power lines or overfilled with electronic devices and appliances, you may consider using shielding cables. Properly installed shielded cables are designed to mitigate EMI and crosstalk while ensuring data integrity and maintain high transmission speed and performance. Shielding not only prevents crosstalk between cables but it can also protect machines and devices, but people as well.
Cables placed inside metal cabinets, enclosures, or away from other sources of noise, typically will not have to be shielded, as they are already protected from noise and EMI. It should be noted that although shielding makes the cable more rigid and robust, they are not to be used in wet locations or direct burial unless they are specifically manufactured for those applications.
What are the Types of Shielded Cable?
Shielded Cable usage is determined by the application. There are various types of shielded cables available in the market, but the 3 most popular types for low voltage signal cables are braid shield, spiral design, or metal-coated Mylar or foil shield. Depending on the design and construction, shielding can reduce noise by 85% to 100%.
Braid Shield 
Braid shielding is constructed by weaving aluminum and copper wires interlaced together. It can reduce noise by up to 90%. Braid shielding can cover up to 85% of the wire and signal noise can leak between gaps in braided weave design. This amount of coverage should be sufficient, especially where applications do not require constant movement flexing. The downside of the braid shielding design is that it is more costly and adds weight to the final design.
Spiral Shield 
A spiral shield is made of conductive wire wrapped in a spiral around the inner cable core and can mitigate noise up to 98%. As with a braid, a variety of materials and wire sizes can be used, however, spiral shields are usually limited to smaller or mid-sized cables in order to attain higher coverage. They are best suited for audio applications because they are not effective above the audio frequency range due to the coil effect created by the inductance or served wire strands.
Foil Shield 
Foil Shields typically use an aluminum foil laminated to a polyester or polypropylene film. Foil shields provide 100% cable coverage, provide strength and added insulation needed for electrostatic shield protection. Foil Shield eliminates the gaps that exist with braided designs to deflect 100% EMI. Foil shielding does not perform well in high-flex applications compared to spiral or braided designs, but they have less weight, bulk and cost less than spiral or braid shields. Tinned copper drain wires are used with foil shields to ground electrostatic discharges and make them easier to terminate. It is important that shielded cables are grounded properly on both ends, in order to get the full benefit of shielding.
Multi-Shield 
Cables may be constructed with multiple layers of shielding with both the braided and foil designs for noisy environments. Communication cables are also designed to be paired and individually shielded, to further aid in preventing cross talk and coupling. Overall shielded cables are where all wire pairs are wrapped inside a single shielded material.
What is the best type of shielding?
The ideal shielding for any application really depends on the specific application for which it is going to be used. Twisted wires are designed to minimize some EMI in unshielded cables, but the added shielding in shielded twisted wire cables is more effective in protecting interference. Shielded cables should also be used with shielded connectors that have some sort of metallic screen or casing that will absorb EMI/RFI and channels the unwanted interference to a ground connection. Shielding efficiency is influenced by resistance, thus making wire-based shields such as spirals and braids shielding ideal for lower frequencies applications. Coverage is the primary issue at higher frequencies making foil shields with 100% coverage the best option, especially in network and communication cables.
For all your shielded and unshielded cable needs, contact Syston Cable Technology. We have a vast range of bulk cables in riser and plenum rating for all your low voltage applications.
As always we are here to help, and if you have any questions about any Syston Cable products, please feel free to contact us via our website or Facebook page.
**Written by Syston Cable Team **
References:
www.wireandcabletips.com
www.wikipedia.org