Selecting the Correct Cable for PoE

Black Box Explains

What Is PoE and How Does It Work?

Power over Ethernet (PoE) lets network cables carry electrical power to any device on a network without an outlet or an adapter. It allows one cable to provide power as well as connect a device to your network.

The way it works is simple. Ethernet cable that meets CAT5e (or better) standards consists of four twisted pairs of cable, and PoE sends power over these pairs to PoE-enabled devices. In one method, two wire pairs are used to transmit data, and the remaining two pairs are used for power. In the other method, power and data are sent over the same pair.

When the same pair is used for both power and data, the power and data transmissions don’t interfere with each other. This is known as "phantom power." Phantom power is accomplished by power being transmitted on the data conductors by applying a common voltage to each pair. Data transmission is not affected since twisted-pair Ethernet uses differential signaling. The center tap of the standard Ethernet pulse transformer is then used to extract the common-mode voltage.

Security cameras, digital signage, video conferencing systems and wireless access points are examples of PoE-compatible devices.

To get the best PoE performance, you need to effectively dissipate heat and keep a cool, stable temperature in your cables. As the temperature of a cable rises, the electrical performance can be degraded. Higher heat dissipation is crucial to increase physical performance and longevity.

What to Consider for Minimizing Heat Generation

Cable Temperature Rating

The temperature rating of a cable indicates the temperature the insulation/jacketing material can sustain. Cables used for PoE have to have a temperature rating higher than 60°C. Common temperature ratings for cables are 60°C, 75°C and 90°C.

Conductor Size/Resistance

Heat generation can be the result of conductor resistance in PoE applications. To improve conductor resistance, choose a cable with a larger conductor size. A CAT6A cable has a larger conductor size than CAT5e cable, providing greater resistance. The greater the conductor size of the cable, the more it can reduce conductor resistance.

Shielding and Jacketing

Twisted pair copper cables for PoE applications are typically F/UTP (four twisted pairs surrounded by some form of shielding in a cable jacket). UTP (unshielded twisted pair cable) is not recommended for PoE applications since it cannot dissipate heat as effectively.

Installation

Installation and environmental conditions can have a substantial impact on PoE performance. To avoid increasing temperature, steer clear of circumstances which could confine heat within a cable such as large bundles, bundles in close proximity and construction or installations that are not within accepted guidelines.

Additional PoE Cable Consideration: Insertion Loss

Insertion loss can be a critical factor when considering the safety and performance of the cable to be used for PoE. Insertion loss can be calculated as the ratio of "received to sent" signal power. More power can result in greater insertion loss levels with rising cable temperatures which may lead to damaged cables.

CAT6A – The Solid Choice for PoE

Your high-performance network depends on the right cabling solutions to deliver speed and power when and where you need it. CAT6A cable is considered future-proof technology that can meet the needs of healthcare, educational institutions, the military and more.

  • Solid copper wire delivers higher performance than alternatives
  • Capable of transmitting 10-Gigabit Ethernet over a distance of 100 meters
  • Offers transmission bandwidth frequency of 500 MHz
  • Improved alien crosstalk characteristics due to insulation and additional, tighter twisting
  • Increased diameter (23AWG) allows for reduced resistance, lower temperature and minimal power waste
  • If you’re planning a large installation in one place, be aware that it also takes up additional space.

All CAT6A Ethernet Cables Are Not Created Equal

By understanding and mitigating risks, demanding quality cables as well as choosing a reputable manufacturer, you can ensure your infrastructure will stand the test of time.

PoE's performance can be affected by inferior cables, counterfeit cables or mislabeled cables. Read more about the danger of counterfeit cables.


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