By CAROL EVERETT OLIVER -- It’s been a year since high-power PoE was defined and ratified by IEEE 802.3bt. So what has changed in the low-voltage industry, and what are the challenges for system designers and contractors when selecting and installing cables for high data and high power?
High-power PoE, more commonly known as Type 3 and Type 4, utilizes all four pairs of a twisted-pair cable; hence, IEEE 802.3bt refers to this as four-pair PoE. Type 3 can provide up to 60W of DC power from the source to a typical maximum of 51W to the device, and Type 4 provides up to 100W from the source to up to 71W at each port.
The good news is that with high-power PoE, more devices, such as digital displays, laptops, televisions, wireless access points and advanced IP cameras, can be powered through the network cable versus having to connect with other cables and to an AC outlet. Think of the freedom! Think of the cost savings! So, what’s the downside?
Overview of Power Types by IEEE Standards
|Nomenclature||Standard||Minimum Power at PSE Output||Maximum Power at PD Input||Number of Pairs||Maximum Current per Pair|
Power over Ethernet (Type 1)
|IEEE 802.3af-2003||15.4 W||13.0 W||2-pairs||350 mA|
Power over Ethernet Plus (Type 2)
|IEEE 802.3at-2009||30.0 W||25.5 W||2-pairs||600 mA|
4-pair High PoE (Type 3)
|IEEE 802.3bt-2018||60.0 W||51.0 W||4-pairs||600 mA|
4-pair High PoE (Type 4)
|IEEE 802.3bt-2018||90.0 W||71.3 W||4-pairs||960 mA|
Turning up the heat
Category cables can power the PoE-enabled device as long as there is sufficient wattage at the source (i.e. a powered switch) to power the unit all the way till the end of the cable run and assure that the voltage has not exceeded the specified voltage drop.
The voltage drop is affected by the end device requirement (typically 48V-57V), cable construction based on individual specifications, and distance of the run. To calculate the voltage drop (V), multiply the current or amps (A) by the cable ohm resistance (W), which can vary between cable types.
With higher power going through the cable on all four pairs, the identified inhibitors are heat build-up within the cable and the distance limitations. It’s still classified as “low-voltage,” so be assured your cable won’t melt or burn -- but be concerned that the internal temperature rise can result in increased insertion loss, which decreases cable efficiency and affects the entire cabling system.
There are standards and codes to help with the design and selection of the proper cable for safety and performance -- NEC NFPA-70 (2017), TIA-TSB-184-A and TIA-569-D-2. Note that TIA and NEC differ in their maximum bundle sizes.
NEC’s focus is safety and the 2017 code provides an ampacity chart (Table 725.144) for up to 192 cables, based on the bundle size, maximum current (A) per conductor, AWG size and cable temperature rating. TIA is concerned with assuring the data and power arrive safely to the powered device and identifies the contributing factors as the current (A) per pair, cable category and number of cables in the bundle (not to exceed 100).
TIA provides recommended mitigation techniques and best installation practices to include: reducing the bundle size (manufacturers’ recommendation is not to exceed 24) ; spreading the cable out within the pathway (such as open cable tray) to provide air circulation; selecting a cable with a larger conductor size (i.e. 22 AWG versus 23 or 24 AWG); and adhering to the manufacturers’ specifications for ambient and installed temperature ratings.
Extending the distances
Since the dawn of Category cable history, dating back to 1983, IEEE 802.3 defined the distance limitation of a four-pair copper cable at 100 meters (which includes the patch cords on both ends). Today, this distance limitation has evolved into an age-old dilemma, and many can’t figure out how this rule came into existence or why it still exists. Why does it? Carol Everett Oliver
One hundred meters was a convenient length, due to legacy specifications for data transmission (10Base-T and 100Base-TX) -- and could be backwards compatible. The longer the run, the more the signal degrades -- and the problem was presumed to get worse at higher bandwidths.
For power, the voltage drop and the resistance of the copper affects the length of the copper distance. Basically, voltage drop depends on the power transmission strength sent at the powered source and the gauge of the copper cable. The restricted reach of 100 meters can severely limit the viable locations where end users can operate a remote IP-enabled device.
Most devices requiring the high power PoE extend beyond the 100-meter limitations – think way-finding signage in an airport, or scoreboards at a stadium, or security cameras in a parking lot. Existing alternatives to extending the reach include running a hybrid copper/fiber cable with media converters and transceivers (which will require AC power), or installing extenders or repeaters for the copper cable.
These options will add cost, as well as more points of failure. (For more information, check out our previous blog: http://www.paigedatacom.com/blog/article/living-on-the-edge-the-good-the-bad-and-the-ugly).
Change the rules by changing the game
It’s a fact that the signal can degrade due to external and internal noise, but with the development of newer and better-manufactured cables, there is a more cost-effective and reliable option. That solution is the GameChanger from Paige Electric.
The patented GameChanger cable supports all four types of PoE out to almost 40% farther than the standard 100-meter distance limitation. Power is carried over the cable's larger 22 AWG conductors and distance is only limited by the data bandwidth and the application -- 10/100BASE-T (10/100 Mb/s) out to 260 meters (850 feet); and 1000BASE-T (1 Gb/s) out to 200 meters (656 feet).
The GameChanger cable greatly reduces any voltage drop concerns with a proven 25%-40% lesser voltage drop than other typical Category cables, due to the GameChanger's excellent resistance rating. (See the voltage drop chart on Paige’s website: http://www.paigedatacom.com/docs/GC%20Voltage%20Drop.pdf).
These cables are designed for all environments, meeting all codes – riser, plenum and outside plant – and are available in unshielded or shielded versions. In addition, they carry a UL listing. There’s no trick, as these cables install and terminate like traditional Category cables, and can be certified by most major field test equipment.
Why play by the rules, when you can change the game?
CAROL EVERETT OLIVER, RCDD, ESS, DCDC was recently chosen as BICSI President-Elect. She will serve a two-year term as President-Elect, in 2020 and 2021, then will take the helm as BICSI President in 2022 and 2023. She will be the first woman to serve as BICSI President. Carol, who currently serves as BICSI’s Secretary, is principal of CEO Communications in Cape Coral, FL.