When looking at cables one should ask themselves about the need for canceling out electromagnetic interference (EMI). While all and any cable type may work for a specific application, it is important to understand where and when the cable will be required to provide protection from power frequency and / or electromagnetic interference (EMI). This is where shielded vs. unshielded cable come into play.
First let’s explore what is Electromagnetic Interference (EMI) or radio frequency interference (RFI) as it may also be called. EMI is a disturbance. This disturbance is generated by an external source affecting an electrical circuit by electrostatic coupling, electromagnetic induction, or conduction. This type of disturbance may lower the performance of the circuit or stop it from functioning all together. Where there is a data path, these types of effects range from an increase in error rate all the way to a complete loss of the data.
Natural as well as man-made sources generate changing electrical currents and voltages that may cause electromagnetic interference. Examples for manmade sources include vehicle ignition systems, cell phones, etc. Natural sources include the sun, thunder storms, etc. Electromagnetic interference commonly affects AM radios, and may also affect FM radios, televisions and cell phones.
Shielded cables reduce electrical noise and electromagnetic radiation. In other words, they help to keep the signal steady, and reduce interference with other devices. This is done with a shield that may be composed of copper tape, a layer of conducting polymer or a braid (made of copper or aluminum mostly), and is covered with a jacket.
There are different levels of shielding. STP, SSTP, FTP. There are also different types of shielding, including braided shield, foil and screening. To make sense of it all, let’s break this down a bit.
The shield can be applied to each one of the pairs in a cable, or to all the pairs together.
Foiled – when the shielding is applied to individual pairs or quads.
Screening – when the shielding is applied to the collection of pairs.
Braiding – a type of shield made of braided strands of aluminum or copper.
UTP – Unshielded Twisted Pair
STP – Shielded Twisted Pair
SSTP – Screened & Shielded Twisted Pair
FTP – Foil Twisted Pair
Shielded cables are thicker than unshielded cables, as well as more sensitive to work with. They are usually used in industrial installations where nearby equipment cause electromagnetic interference.
Unshielded twisted cables (UTP) by definition do not have shielding serving them to reduce interference. They are designed to cancel electromagnetic interference with the way the pairs are twisted inside the cable. Due to its design and nature, unshielded twisted cable is most suitable for office LANS and similar network cabling systems. Unshielded cables are lightweight, thin and flexible. They are also versatile and inexpensive. When properly installed, a well-designed unshielded cable will be easier to both install and maintain than a shielded one.
It is important to know the difference between the types of cables, their applications and pros and cons in order to make a knowledgeable decision which cable type to use, where, when, and why. Choosing the right cable type with enhance the network’s performance, minimize errors and allow for a long life span.