UTP vs. STP Cable: Understanding The Real Difference

Category or “CAT” cables are a family of copper cables used for signal transmission in data networks — they represent one type of structured cable and are commonly called ethernet cables. The International Organization for Standardization/International Electrotechnical Commission (ISO/IEC) standard 11801 contains the specifications for CAT cables as well as other structured cables.

There are eight generations of CAT cable not counting the multiple variations within each generation. CAT 5e was the gold standard networking cable for nearly 20 years, but it has since been replaced by Cat 6 and CAT 6a. However, each cable type and iteration requires different equipment and infrastructure if you want to see maximum performance.

The simple answer is that UTP is short for “unshielded twisted pair” and STP is short for “shielded twisted pair”. Both are types of twisted pair cable, but in this article, we’ll unpack the differences and provide some guidance about when to use UTP vs STP cable.

In order to understand why shielding is important, we need to dive into the crazy world of electrical signals and signal transmission. Ethernet cables are comprised of four pairs of insulated copper conductors twisted together and bundled within a PVC jacket. They often include a spline (to separate the pairs) and ripcord for tearing through the outer insulation and assisting with pulling.

When an electrical signal passes into the conductor, the signal is measured by a transceiver that measures the difference between the voltage of the two wires in each pair. If you could see electrical fields, you would notice that even though each wire is covered with PVC insulation, there is still a halo or weak electrical field surrounding each wire. Insulation prevents electrical shorts, but PVC does not block the electrical field, it only dampens it.

If an electrical field is strong enough, your cable will experience crosstalk, a phenomenon where the electromagnetic interference from one set of wires affects the performance of another cable. This reduced performance is referred to as attenuation. In short, crosstalk causes signal attenuation or poor performance.

From a practical standpoint, even if you install a high-speed data network, if you haven’t planned for and addressed crosstalk and attenuation, you’ll experience reduced speeds and packet loss (where signals are obscured beyond the point of usefulness).

Twisting the pairs of wires together helps reduce crosstalk within the ethernet cable itself and into other nearby cables. However, it doesn’t eliminate the problem altogether.

In order to prevent crosstalk, engineers determined that individual pairs could be wrapped with a foil “shield” and the invisible electrical field emanating from each pair would be funneled along the shield and grounded out at the terminal. Think of the shield as a path of least resistance for that electrical energy. When the entire bundle of four pairs is covered by a single foil shield, it is classified as a shielded, twisted pair or STP cable. In the absence of foil shielding, the cable is classified as an unshielded, twisted pair or UTP. There is another designation for shielded cable known as FTP where each of the four pairs is covered by a foil shield. FTP offers the greatest performance in terms of low crosstalk and attenuation, however, it is also the most expensive by the foot and is more complex to install.

For the purposes of this article, we’ll focus on STP cable for the sake of simplicity, since FTP is a more thorough application of the same shielding principle.

Generally speaking, the crosstalk between data cables is relatively minor. The biggest risk for crosstalk comes from AC power cables or high voltage equipment that may operate near your data cables. If you’ve evaluated the pathways your data cables will run and identified potential sources of high-voltage interference then you have also found situations where STP cable is called a good idea.

But it isn’t as simple as buying different reels of cable and hooking it up to the exact same equipment. Due to the composition of STP cable, you need specific installation equipment, different terminal connectors, and different equipment to take full advantage of the STP performance without causing unwanted problems. Improperly installed STP cable can leave you worse off than just using UTP and dealing with crosstalk.

The various cable types, such as UTP and STP exist because they serve distinct purposes. The type of cable your project needs can change literally from room to room, depending on the environment and the electrical infrastructure nearby.

Your best bet is to partner with a vendor who can look at your building plans, or evaluate your existing layout and determine which cables will perform the best — without losing sight of your budget.

i.e.Smart Systems is a Houston, TX based technology integration partner that specializes in design and installation of audio/visual technology and structured cabling. For more than three decades, our team of in-house experts has partnered with business owners, architectural firms, general contractors, construction managers, real estate developers, and designers in the Houston market, to deliver reliable, scalable solutions that align with their unique goals.