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Cabling and Connectivity for Power over Ethernet

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LEVITON.COM/CROSSTALK 1

Cabling and Connectivity for Power-over-EthernetPower over Ethernet (PoE) has made great strides in recent years. Driven by the demand for ease of installation and boosted by new standards that expand support to more devices, PoE is expected to see explosive growth rates that match the period shortly after the technology was initially introduced in 2003.

There are some appealing reasons for adopting PoE. Foremost, by running power and data transmission over the same cable, PoE eliminates the need for additional wiring installations, saving on money and redundant cabling. This consolidation also allows for faster deployment at the endpoint, especially to devices at far off building locations such as warehouse transactions work areas, security cameras, sales kiosks, etc. And remote power feeding allows power to be consolidated into one central location.

While earlier standards limited the types of devices that could be supported by PoE, recent standards have allowed for higher power transmission, expanding the range of devices supported in the enterprise and in turn further driving adoption rates. However, higher current PoE brings important cabling and connectivity considerations when ensuring utmost performance in the network.

Cabling for PoEOne of the biggest issues that can affect performance is heat generation in cable bundles. When power is added to balanced twisted-pair cabling, the copper conductors generate heat and temperatures rise. The heat dissipates into the surrounding area until a stable temperature is reached, with the cable bundle at a higher temperatures than the surrounding ambient temperature. High temperatures can lead to higher insertion loss and in turn shorter permissible cable lengths, as well as higher power costs due to more power dissipated in the cabling. As recent PoE standards allow for higher power transmissions, temperature concerns will likely become even more prevalent.

Cable temperatures should not exceed the temperature rating for the cable, and cables for commercial typically have a maximum temperature rating of 60 degrees Celsius. The Telecommunications Industry Association (TIA) recommends 15 degrees as the maximum allowed temperature rise above ambient as a result of power over the cabling.

The TIA suggests a number of ways to help lower cabling temperature:

continued on pg. 2

By Grayling Love, Senior Product Manager for Leviton Network Solutions

VOL. 5 ISSUE 6 NOV / DEC 2014Your Source for Industry News & Insight

PoE

The November/December 2014 CrossTalk will be the last printed issue. If you currently receive a print only subscription, you can request the electronic subscription at Leviton.com/crosstalk.

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PAPERLESS!1 Reduce the number of cables per bundle

Separating large cable bundles into smaller bundles or avoiding tight bundles will minimize higher temperatures. For example TIA tested the temperature of a bundle of 91 cables, and then separated that bundle in to three bundles of 37. The temperature in the center of a 91 cable bundle was higher than the worst case temperature in centerpoint of three bundles. Physically separating the three bundles from each other further reduced the maximum temperature.

Use Higher Category Cabling

Higher category-rated cable typically means larger gauge sizes, and as power currents increase, these larger conductors will perform better than smaller cable. Figure 1 shows TIA testing that compares temperature rise to increasing cable bundle size for different category ratings and their wire gauges. All cables were tested using a current of 1000 mA per pair. The test shows that higher category-rated cable allowed for larger bundle sizes under the maximum 15-degree temperature increase. The allowable bundle size was 52 cables for Cat 5e, 64 for Cat 6, 74 for Cat 6A, and a similar increase for Cat 8.

2

Number of Bundled Cables

Temperature Rise (°C) — 1000 mA per pair

Cat 5e (24 AWG) Cat 6 (23.5 AWG) Cat 6A (23 AWG) Cat 8 (22.5 AWG)

52 15.0 12.4 10.9 10.161 17.4 14.5 12.7 11.764 18.1 15.0 13.1 12.274 20.7 17.2 15.0 13.991 25.4 21.1 18.3 16.9

(source: TIA TSB-184)

Figu

re 1

Cabling and Connectivity for Power over Ethernet • continued from pg. 1

2 LEVITON.COM/CROSSTALK

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0 10 200 300 400 500 600 700 800 900

Current Per Pair, mA

Tem

pera

ture

Ris

e, D

eg. C

Category 5e

Category 6

Category 6A

(source: TIA TSB-184)

3

Figure 2 compares the temperature rise in 100 cable bundles of Category 5e, 6, and 6A, as the current per pair increases (over all four pairs). Again, the higher-category cabling is able to support more current capacity at the maximum allowable 15 degrees, as the Category 6A bundle supported 865 mA per pair. It becomes clear that higher category cabling will be necessary to minimize temperature increases while supporting PDs that require more power. For this reason Leviton recommends using Category 6A for new 4-pair PoE applications.

Install Shielded Cabling

Leviton engineers recently tested how heat affected performance in Leviton Category 6A cabling. They compared three cable types: Unshielded Twisted Pair (UTP), Foiled Unshielded Twisted Pair (F/UTP), and cable using Leviton patented Noise Canceling Helix Technology (NCHT). NCHT cable includes a metallic “isolation wrap” that surrounds the 4-pair core, and features separations in the wrap to prevent a current from flowing along the length of the cable. This isolation wrap provides additional alien crosstalk suppression, but eliminates the need for grounding and bonding typically required with shielded cabling.

The samples of cable were tested carrying a PoE+ current of 600 mA per pair over all 4 pairs at an ambient temperature of 60 degrees Celcius. Each cable type was coiled into a separate 90 meters length and terminated with jacks at both ends. They then applied the current while monitoring the temperature rise of the bundle.

If the test result passed insertion loss requirements from TIA-568-C.2 and ISO/IEC 11801 Class EA, they would end the test for that cable type. If the result failed, they removed 1 meter of cable from the coil, re-terminated, and re-applied the current, then took another measurement. They continued this process until obtaining a passing result.

The insertion loss length de-rating varied considerably between the cables tested, as listed in Figure 3. The UTP cable exhibited the worst performance, as it required more than 9 meters of length to be removed before it returned a passing insertion loss result. The F/UTP and NCHT cables performed significantly better, with the NCHT cables requiring only 1 meter of length removed, and the F/UTP cable still passing at 90 meters.

The large difference in performance between UTP and the other cables at elevated temperatures is likely because UTP cable has no shield or isolation wrap barrier between the insulated conductors and the outer cable jacket material. In turn, there may be an interaction that changes the dielectric constant around the conductor and contributes to greater attenuation at higher temperature.

It is important to note that while insertion loss varied between F/UTP and NCHT cable types, there are pros and cons for every cable type. While F/UTP fared the best, NCHT offers the benefit of no grounding or bonding, and it is easier to terminate. These considerations should be made based on your specific network application.

Figure 3: Insertion Loss vs. Temperature for 90m PL

Temp Cable PL LengthIL Margin (dB)

TIA ISO

~20 °C

UTP

90 m 4.1 1.9

60 °C

90 m -4.5 -6.6

89 m -3.9 -6

88 m -3.4 -5.5

87 m -2.9 -4.9

86 m -2.5 -4.6

84 m -1.1 -3.1

83 m -0.9 -2.9

82 m -0.4 -2.3

81 m -0.1 -1.9

80.8 m 0.6 -1.8

~20 °C

NCHT

90 m 4.1 1.9

60 °C90 m -0.1 -0.4

89 m 2.7 -0.2

~20 °CF/UTP

90 m 5.8 3.6

60 °C 90 m 3.9 1.7

Connection ReliabilityAnother consideration with higher current PoE is the potential for damage over time to RJ-45 connectors in the network. Specifically, when a patch cord is unplugged while the connection is charged, an electrical arc will occur between the connector and the plug. While there is no immediate damage (and the arc is not dangerous to users), the integrity of the connection can become weakened over numerous disconnections.

To add extra protection and longevity to the life of the connection, Leviton recommends using connectors with 50 µm gold-plated tines (as specified by TIA standards), as well as designs that distance the connection point between the connector tines and plug from the arcing damage. They should also meet contact resistance requirements found in the IEC 60512-99-001 standard covering connectors for electronic equipment.

Leviton tested the placement and severity of pitting on the Leviton connector tine set resulting from electrical arcing across the contacts when plug and connector are disconnected in an energized PoE+ application. The test found that pitting developed on both the connector tines and the plug contacts after 25 insertion cycles, with increased damage after an additional 25 cycles with reversed current flow.

Green line = Point of contact between connector tine and plug when mated

Red line = Point where pitting damage occurs from PoE+ disconnect while energized

Figure 2

However, the location of the pitting in Leviton connectors is sufficiently far from the point of contact between the tines and plug contact when the connectors are mated, as shown in Figure 4. This means that the pitting does not affect the electrical performance of the connectors within a channel, providing additional longevity.

Read more about connectivity and standards for PoE at Leviton.com/CrossTalk.

Figure 4

Email: crosstalk@leviton.com

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INDUSTRY802.11ac wireless access point market penetration has nearly doubled every quarter, taking increasing share from 802.11n access points, according to the Infonetics LAN Equipment and WiFi Phones report.

Leviton opened a New Office in Mexico City in September. The opening included a ribbon-cutting ceremony and guided tours of the new facilities. Leviton was also a Gold Sponsor of this year’s DataCenter Dynamics

Converged convention in Mexico City, held October 1-2. The event included a presentation by Leviton VP Data Center Technology, Maurice Zetena, on optimizing the data center’s physical layer.

LEVITON.COM/CROSSTALK 3

Cat 6A cables are heavier than Cat 6 and 5e, and require modifications to traditional structural and support techniques.

PRODUCTNew Compact DIN Rail-Mount Boxes are ideal for network patching inside industrial automation and control panels. The boxes are available empty or with a Leviton 6-Port QuickPort® Decora® insert installed, and can be opened to install other QuickPort Decora inserts if required. The back panel of each box can be configured to allow cable access at either the top or bottom, thereby increasing flexibility within tight control enclosures. Box depth is suitable for Cat 5e and Cat 6 connectors.

The Network Solutions Data Center Design Team works closely with customers to understand their needs and provide an optimal plan for deploying structured cabling solutions in the data center.

Recently, the team played a vital role in assisting with the deployment of an advanced structured cabling solution for a major cloud-based customer relationship management firm. The customer required a unique leaf/spine configuration that was an entirely new topology for the company. To ensure the customer was getting the full benefit from their network, a member of the Leviton team arrived on site to get a first-hand look. He created a mockup of the network for the customer, and it was deployed shortly after. Since installation, the customer has replicated the Leviton-recommended design in four other facilities around the world.

The team also recently aided a high-profile global communications company with a leaf/spine topology incorporating SAN. Again, a member of the Data Center Design Team traveled to the site to obtain a clear understanding of the customer’s requirements. He compiled an in-depth design proposal and a customized bill of materials that precisely outlined the customer’s connectivity needs. The proposed layout is currently being installed and will include Leviton flat and angled e2XHD patch panels, MTP® cassettes, and MTP fiber trunks.

“The Leviton Data Center Design Team has more than 75 years of combined data center expertise, including Leviton Vice President of Data Center Technology, Maurice Zetena, who works directly with international data center customers,” says Scott Robinson, Leviton Senior Director of Technical Services. “Working with the Leviton Sales Team, we strive to engage our customers as soon as they need us, wherever they need us. And by providing custom bills of material, custom rack and cabinet drawings, and custom design materials, we are able to deliver tailor-made solutions that meet our customers’ specific requirements and maximize their return on infrastructure investment.”

Learn more at Leviton.com/datacenter.

Leviton Network Solutions Data Center Design Team

YESTERDAY’S NEWS1954: DYSEAC, built by the National Bureau of Standards for the US Army Signal Corps, was one of the first “portable” computers. Portable in the sense that it could be loaded into a tractor trailer and transported to other locations as needed.

Tips for Handling Cat 6A Cable Bundles

COMPANY

Follow the tips here to help ensure a smooth installation:

1. Use stronger anchors and threaded rods to support CAT 6A cable

2. Use properly-sized J hooks and other supports to accommodate bundle size

3. Limit bundles to 50 cables to prevent damage to cables on the bottom

4. Do not exceed cable support manufacturer’s recommended capacity

5. Space cable supports randomly between three and four feet apart to prevent system degradation due to sagging

6. Do not use ceiling support wires or other ceiling components to support communications infrastructure

In November we introduced New Software Features for the Intact Intelligent Port Management System. With these enhancements, Intact now provides asset management capabilities by extending monitoring beyond the telecom room, all the way to the desktop, detecting the presence of active equipment throughout the channel. The software enhancements can be downloaded at Leviton.com/Intact.

Intact Intelligent Port Management System

6

ASK THE EXPERTSQ: If OSP cable is kept in conduit, can contractors run past the “50-foot rule” before converting to ISP rated cable?

A: Yes, as long as the conduit is uninterrupted. The transition has 50 feet once the cable exits the conduit. For example, if the cable enters the entrance room, exits the conduit, and enters another conduit to leave the room, the conduit is interrupted and the 50-foot rule (NEC Article 800-50) will be applied.

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CROSSTALKVOL. 5 ISSUE 6 NOV / DEC 2014

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