Shielded vs. Unshielded Cable

Written by Don Schultz, trueCABLE Senior Technical Advisor, Fluke Networks Copper/Fiber CCTT, BICSI INST1, INSTC, INSTF Certified

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Many people who install bulk Ethernet data cable wonder if standard unshielded cable (UTP) is good enough, or if higher-end shielded cable (FTP) is necessary. Shielded must be better, right? Before we get into which one is “better” let’s take a look at the similarities and differences of shielded vs. unshielded networking cable.

Note on all this UTP, U/UTP, and F/UTP stuff:

Installers commonly and generically refer to unshielded Ethernet cable as “UTP” and shielded Ethernet cable as “STP”.  This is misleading and confusing.  For this blog, U/UTP means fully unshielded Ethernet cable.  Shielded Ethernet cable comes in several different varieties and can be seen as F/UTP, SF/FTP, U/FTP and more.  For the purposes of this blog, the type of shielding is not relevant. Read Ethernet Cable Shielding Types to learn more.

Similarities

Unshielded and shielded Ethernet cable:

• Use keystone jacks, patch panels, and RJ45 8P8C connectors for termination
• Have eight inner wires arranged into four color coded 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 T568A or T568B standard
• May have an internal “spline” cross skeleton to help mitigate internal pair to pair crosstalk.  Splines are typically seen in Cat6 and Cat6A Ethernet cable to help achieve the necessary performance to carry data at higher speeds.
• The tools used to terminate both cable types are largely the same
• Run length distances are the same for both cable types, given ambient temperature is at 68℉ or less.  Shielded cable is not used to defeat normal length limitations, but may help at higher temperatures.  More on that later.
• 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

Shielded Ethernet Cable:

• Is more of a challenge to install due to weight, reduced permitted bend radii, overall construction, and cable thickness
• Costs more per foot
• Requires more expensive shielded connecting hardware in order to work as intended
• Contains shielding in the form of aluminum foil, aluminum braid, or both
• Contains a dedicated ESD (Electrostatic Discharge) drain wire to help drain off static electricity build up in the cable.  The drain wire works in conjunction with the cable shield.
• Must be bonded to ground properly and if not, can actually introduce issues as opposed to resolving or avoiding them
• May induce undesirable ground loops when installing the cable between buildings

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:

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EMI/RFI issues:

• 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 Installations

Outdoor aerial installations bring significant risk of ESD (electrostatic discharge) into consideration. Shielded Ethernet cable, in conjunction with Ethernet surge protection, is used to mitigate that situation. See When Lightning Strikes! Ethernet Data Cable and Lightning Protection for more about that shocking subject.

Ambient Temperature Issues

Shielded Ethernet cable can be used, within reason, to allow additional run length.  No, this does not mean you can use shielded Ethernet to ignore the 328 foot rule.  When ambient temperatures rise above 68℉, permitted run lengths for any kind of Ethernet cable get shorter.  This affects unshielded and shielded Ethernet alike, but the effect is less severe upon shielded Ethernet cable.  See Temperature's Effect on Ethernet Cable Length for specific guidance right down to the foot and degree.

There are other scenarios that may trigger the installation of shielded Ethernet cable:

• PoE installations, especially large bundles carrying 60W DC or higher installed  in conduit, will benefit
• Edge case scenarios where alien crosstalk (ANEXT) is an issue.  Often seen when pushing a large bundle of Cat6 Ethernet cable to 10Gb/s.  

Knowing your environment and possible trouble areas might let you get away with installation of U/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 Mr. Murphy

It is possible to self-inflict problems when installing shielded cable. It requires proper bonding to ground, as the unwanted external interference is channeled down this shield (and the ESD or drain wire) to ground. Shielding in the cable functions as a block and path; it is a path of least resistance.

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The Ground Loop