Shielded vs. Unshielded Cable
Written by Don Schultz, Networking Consultant & trueCABLE Customer
Many people installing data networking cable wonder if standard unshielded cable (UTP) is good enough, or if higher-end shielded cable (FTP) is necessary. Generally, unshielded cable will serve your purposes well. Let’s take a look at the similarities and differences of shielded vs. unshielded cables.
SIMILARITIESBoth types of cable:
- Use RJ45 connectors
- Have eight inner wires arranged into four twisted pairs
- Usually contain a rip cord to open the cable jacket, although most of the time you will use a strip tool to achieve concentric ends
- Are always terminated according to the TIA 568 A or B standard
- May have a “spline”
- Splines are an internal, cross-shaped plastic skeleton that keeps each twisted pair together, but also separate from the other pairs. This greatly reduces cross talk and attenuation between pairs. Splines further assist in maintaining twists in the pairs and reduce kinking during installation
- For the most part, you may use the same hand tools to perform cable preparation and termination...however this is not always the case
- And both cable types perform the exact same basic function, which is the delivery of data signals and possibly PoE (Power over Ethernet) from point A to point B
THE DIFFERENCESFTP Cable:
- Is more of a challenge to install due to construction and overall cable thickness
- Costs more per foot and requires more expensive shielded connecting hardware in order to work as intended
- Contains shielding in the form of aluminum foil, aluminum braid, or both
- Usually contains a dedicated ESD (Electrostatic Discharge) drain wire to help drain off static electricity build up in the cable
- Must be grounded properly and if not, can actually introduce issues as opposed to resolving or avoiding them
- Due to cable thickness, might require a stronger/larger termination tool for shielded RJ45 connectors
HOW DO I KNOW IF I NEED SHIELDED CABLE?
In the decision process between unshielded (UTP) vs. shielded (FTP) cable, it is the environment the cable will be installed in that makes the ultimate determination. If one or more of the following common scenarios applies, then shielded cable is strongly suggested:
- Alongside (parallel) with common AC wiring, especially inside walls
- Proximity to high voltage wiring or panels
- Within a few feet of generators or electrical motors
- Outdoor installation
- Critical backbone connections such as switch to switch, switch to server, or when the connection absolutely must have the highest possible speed the devices on either side can support.
AVOIDING MR. MURPHY
It is possible to self-inflict problems when installing FTP cable. It requires proper earth grounding, as the unwanted external interference is channeled down this shield (and the ESD or drain wire) to ground. Shielding in the cable is not a “block”, it is a path of least resistance.
THE GROUND LOOPImproper installation and use of FTP cable may result (in rare cases) in equipment damage, due to unintended consequences like ground loops. Ground loops occur when there is more than one path to ground and one of those paths happens to have a different voltage potential. Take, for example, two buildings. Each building has electrical service (known as a “main”). Can FTP cable be run safely between these two buildings, especially if there is a path to ground at both ends of the cable? If there is a different electrical potential between the grounds of those two buildings, then issues may occur. In most cases, the cabling will present intermittent problems like packet loss on the network which will be difficult to track down. In more extreme cases, a piece of equipment will receive a voltage injection and end up destroyed if the voltage potential between AC grounds is large enough. There are workarounds for this, well beyond the scope of this article.
THE ANTENNA YOU DID NOT KNOW YOU HAD
So, what could happen if FTP cable is installed without the shield being properly grounded? The FTP cable in question has no place to channel unwanted external energy safely...so it may very well act as a massive antenna.
More commonly, improper installation of FTP cable will simply result in wasted money, time, and effort. Murphy's Law will dictate what else might occur if the proper installation technique is not observed.
Check out this infographic on selecting Shielded vs Unshielded cable.
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