Shielding is the most efficient way to stop any kind of physical damage against electrical wires. It’s possible to have a 15-ton truck park on it overnight (wouldn’t that be nice). Shielding although it sounds like it may protect from physical abuse, it is quite the opposite. Shielding wire is done for the sake of combating EMI or Electromagnetic Interference, “this is when the radio frequency spectrum, has a disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electrostatic coupling, or conduction” (Wikipedia). https://en.wikipedia.org/wiki/Electromagnetic_interference
Shielding stops 4 large issues that are common with transmission:
Crosstalk: Is when another signal line is wired wrong or has a weak outer shell, which causes connections to meld together. Crosstalk is also when two phone lines begin to connect to one another and 2 separate conversations merge together.
Magnetic noise: Magnetic noise is similar to the others, as it is defined as hissing noise created as a result of transmission lines creating a corona discharge. It is also commonly referred to as audible magnetic noise, magnetic acoustic noise or even electrical coil noise.
Common mode noise: The common mode noise typically has a higher frequency range than other forms of electrical noise. It’s created by something called a “magnetic flux”, which is when differential mode current starts to cancel one another and has no impedance.
Static noise: static noise is a common problem that occurs especially when wires are poorly insulated or have to handle larger voltages. Static noise is caused by other voltage sources that are wired into the same signal circuit
All 4 of these different classifications of noise have negative outcomes for every application they appear in. Shielding is, therefore, the main way to protect the wire. From shielding there comes…
The 3 classifications of noise
High Noise- created typically by heavy motors, generators, power lines, induction heating, relay control and electrolytic processes. The high-level noise is commonly in locations like heavy processing plant, mills and steel foundries.
Medium Noise- Wiring near motors and transformer relay control, which are typically used in the average manufacturing plant.
Low Noise – The wiring source is often located from power lines, motors, and control or power relays. This low noise level can often be found in offices, storage areas and in medical or other forms of laboratories.
When it comes to shielding there are 4 main types of standard shielding options, each of which has its own unique attributes that make them stronger than the others in different applications:
Braid: The braided shield has good flexibility and has the material of the shield interwoven into a tubular structure or a rectangular cross-section. The braided shield is also the oldest form of shielding that is still currently used. These braids come in many different material types like steel, aluminum, copper, tinned copper, silver plated copper & bare copper, while occasionally using fiberglass for the additional strength it offers. The braids only have 55% to 95% coverage. This type of shielding is still used, but the braider (the machine that creates the braid) takes a long period of time and the braid is commonly more expensive than the other alternatives.
- Core size: .012" and larger
- Frequency range: Low to mid frequencies (Up to 100 MHz)
- Flexibility Good
One of Sycor's popular Braid Shield products:
Spiral: Spiral shields often are created out of bare, tinned or silver plated copper strands, while other metals such as steel may be used for additional physical protection. Spiral braids have the highest flexibility and can be easily manufactured with 95% coverage, with less weight than the other shields. The Spiral shields have the wiring material wrapped around a core with 95% to 98% coverage. The spiral shields are effective in applications involving audio frequency and within other audio wiring applications like a microphone or audio applications.
- Core size: .004" - .450”
- Frequency range: Low frequencies (Up to about 1 MHz)
- Flexibility Very Good
Foil: Foil shields appear in the shape of a foil gum wrapper and are almost always constructed with tape being either Mylar or Aluminum. Being typically constructed with drain wire while still providing 100% shielding, allows for effective higher frequencies. Adding an additional drain wire allows for easy termination and it must be in contact with the metallic part of the shield. With the foil shield, the drain wire must additionally be 1 size smaller than that of the conductor it is terminating. The foil shield is also not recommended for continuous flexing applications, while the termination options are often limited. This specific option is also not strong at withstanding continuous flexing applications.
- Core size: .025" and Larger
- Frequency range: High frequencies (Greater than 100MHz)
- Flexibility Poor
Some of Sycor's popular Foil Shielded products:
- Multi-Paired Individually Foil Shielded Computer Cable
- Multi-Paired Individually Foil Shielded (Low Capacitance) Computer Cable
- Multi-Paired Overall Foil Shielded Computer Cable
- Multi-Paired Overall Foil Shielded (Low Capacitance) Computer Cable
- Multi-Conductor Overall Foil Shield
Combination Shields: Are created from 2 or more shields that are created into a single cable. The most common type of cables to combine is the braid over foil or braid over braid. The combination shield is typically used for its 100% foil coverage, mechanical strength, its physical protection, the low DC resistance and flexibility. Combination shielding often comes in a tri-shield or quad shield that adds additional protection to the outer braid. The combination shielding also isolates conductors thereby decreasing the chance of EMI and crosstalk between conductors.
One of Sycor's popular Combination Shielded products:
Additional EMI blocking methods
Being an important part of major telecommunication industries other forms of EMI blockers have been developed and refined. Although these new developments are still not as efficient as shielding, they do offer additional protection where signal reliability is essential. One of the most popular developments in this field is known as “ferrite Beads”. These beads are not a shield, but they do reproduce the effect of shielding and can be used after non-shielded wire has been installed. These beads are placed around each wire and stop any unwanted energy by grounding any electricity.
Shielding is an important part of a cables make up, especially in the communication industry. Each type of shield has pros and cons that work better and worse in different environments. Choosing the right wire can depend on many factors like the type of environment, grounded or ungrounded, amount of flex required and frequency range. Sycor offers all of these shields and has an expert sales team to help guide and answer any questions you may have.
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