Shielded vs. Unshielded Cable

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 service your purposeless well. Let's review the similarities and differences of shielded vs. unshielded cables. 

SIMILARITIES

Both 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 DIFFERENCES

FTP 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.

There are other scenarios that may trigger the installation of FTP cable. Knowing your environment and possible trouble areas might let you get away with installation of UTP instead. Even if FTP cable is run, it is advisable to take all reasonable precautions to avoid spots of heavy electromagnetic interference/radio frequency interference (EMI/RFI).

AVOIDING PROBLEMS

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 LOOP

Improper 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.