Power over Ethernet technologies, standards and applications

Q: Concern has arisen over erosion and/or damage to jacks caused by plug/jack mating while PoE is employed. Can you describe this issue, and how it can be prevented?

Tremblay: Issues related to invalid PoE device detection, no power delivery, and Ethernet data corruption are commonly related to excessive wear on the gold-plated contact pins inside the RJ-45 connector. PoE equipment suppliers source RJ-45 connectors from various component manufacturers, which can provide a wide range of gold-plating thickness. Recommend deploying PoE equipment using RJ-45 connectors with a minimum of 50 micro-inches of gold-plating thickness.

Jones: IEC 60512-99-001 specifies unmating under load with 500 mA per conductor requirements. Ensure both sides of your connector have been tested to this requirement. But in general, a well-designed RJ-45 pair will have the “wiping zone” a decent distance away from the “seating zone” such that if any pitting were to occur from unmating that the damage would not affect normal operation. Due to the layer of safety IEEE-compliant PoE adds via the mandatory detection (the PSE never applies power until it has discovered a PD that requires power), there is no worry of arc damage on mating. Additionally, a large percentage (in the high-90% range) of PoE devices are placed into service and never disconnected until they are being replaced. This really isn’t an issue unless one is unplugging devices a lot.

Maguire: Unmating a jack-plug connection under PoE load produces an arc that erodes the plated jack-plug contact surfaces at the arcing location. While not a safety concern, when this erosion occurs in the area of the fully mated position, the result is an unreliable connection that can result in bit retransmissions or even cause the network switch to auto-negotiate to a lower transmission speed. Modular plugs and outlets that have designs, such as “crowned” contact geometry, that shift the final mating interface away from make-first/break-last contact connection points ensure that arcing damage occurs far away from the final mated position.

IEC-60512-99-001 was specifically developed to ensure reliable connections for remote powering applications deployed over balanced twisted-pair cabling. It specifies the maximum allowable resistance change that mated connections can exhibit after being subjected to 100 insertion and removal cycles under a load of 55V DC and 600mA applied to each of the 8 separate plug/outlet connections. To ensure reliable performance and contact integrity, modular plugs and outlets supporting PoE should be independently certified for compliance to IEC 60512-99-001.

Straka: When a plug is removed from a jack in a system that is actively running PoE, a spark (arc) can occur briefly between the plug and jack contacts. This spark can create some minor carbon scoring. This issue has occurred in all PoE circuits, but with the higher power standards coming online this arcing and carbon scoring gets more severe. In cases where the plug and jack are removed several times, this carbon scoring can build up and lead to data transmission issues between the plug and jack. This issue cannot be prevented, but with good connector design it can be mitigated. For instance, our jacks are designed so that the place where the arc occurs is at a different location from where the plug’s nominal resting point is. The jack’s contacts also allow for significant scraping when inserted to remove any carbon buildup that may occur.

Tellas: It’s important to note that plug/jack mating isn’t the issue. In order for erosion or damage to occur, there must be a “handshake” between the device and switch to bring power to it. If an active device with a PoE connection is unplugged, then an arc (spark) will occur between the plug and jack contacts. This may cause connection problems and damage jack and plug contact points. The best way to ensure that you don’t create this arc is to turn the device off before disengaging the jack. In addition, the connecting hardware you install should pass IEC 60512-99-001 test methods. In a successful test, after 100 cycles at 600 mA, the contact resistance change must be <20 mΩ. This ensures that, if someone disengages the jack before the device is turned off—or if the device can’t be accessed—an arc won’t cause damage.

Q: Delivering power via PoE can raise cabling-system design and installation issues—for example, bundle-size limits to minimize heat rise, and closely examining cable length/slack to reduce power loss. Please share any design or installation best practices that can help ensure a capable and efficient PoE-ready cabling system.

Malkemus and New: Choosing the highest LP-rated cable or larger copper size would be the first consideration. This provides the highest capability available and will futureproof the installation to allow it to support current and future powered devices. Also, keep under the maximum allowable pulling force for the cable. Surpassing a cable’s rated pulling force can stretch the conductors. Stretched conductors change the copper’s diameter and reduce the current-carrying capability of the cable.

Ensign: There are guidelines by UL, BICSI, and TIA for maximum bundle sizes, which are good to follow. What is going to make this work with the least amount of risk is using the right cable for higher power PoE. It’s always recommended to follow industry best practices and standards from BICSI and TIA. In regard to cable slack, we will want to do all we can to limit the length of cable, as the longer the length, the more power drop, which means less power to the PoE device and the harder the PoE injecting or source equipment will need to run. This also leads to lower overall power efficiency and costs.

To help with bundle temperature increases, it is still OK to install nice-looking well-dressed cable bundles using hook-and-loop straps. If there is an option to “open” the bundles or use smaller bundles to increase the available airflow around the cables, it is a good thing to do to alleviate any temperature increases. At the time the cable is installed, we should have a good idea of what the PoE applications are—but what about three years from now? The PoE power level may be higher due to new applications. We need to ensure we are taking that into consideration, which is why cable selection matters.

Jones: PoE bundling was added to the National Electrical Code in 2017 due to fears of large bundle heating. Nearly right away, the 2017 NEC was amended to add an exception for systems with 0.3 Amps/conductor, and 24-AWG cable (the minimum standard gauge for horizontal cabling), because in these cases the heating is manageable even for more than 192 cables in a bundle. This exception is important because it means IEEE 802.3af (PoE Type 1), IEEE 802.3at (PoE Type 2), and IEEE 803.2bt Type 3 systems can be installed on standard cabling without concern. Bundling only becomes a concern when using IEEE 802.3bt Type 4 PoE or smaller than 24-AWG cable, and even then can be managed easily. If the current per conductor is greater than 300 mA, the following paragraphs provide guidance.

Category 6A is typically 23 AWG and Category 5e is typically 24 AWG; a Category 6A 75 deg. C cable can be used in bundles of 192 and Category 5e 75 deg. C cable can be used in bundles of 91. There is a tremendous amount of power supplied into these theoretical large bundles. This is unlikely to be found in the typical install. Additionally, that large bundle wouldn’t all run from point A to point B. It would get broken down into smaller bundles along the way, further reducing the chance for bundle heating.

For the installer that doesn’t want to think about it, and make it easier on the inspector, go with smaller bundles—37 or fewer cables. Bundles of 24 naturally form from typical network gear. You can loosely group these bundles while still in the air-conditioned telecom room and as they exit the room. Immediately separate the small bundles by 1.5 inches once in the plenum. This will provide a path to an easy inspection and futureproofing in case the new install isn’t presently using Type 4 PSEs by having the cable plant ready for equipment upgrades.

If you are using equipment that is labeled PoE but is not IEEE-compliant (e.g. does not have the Ethernet Alliance PoE certification logo), the installer or designer will have to determine the conductor current and then likely walk the inspector through the design details. In this case, using LP cable is recommended as it will be designed to a specific current level for bundles up to 192. This will make the inspection easier as the inspector can look at the required marking on the PSE and the current capacity of the cable and ensure they properly match.

Tellas: Paying attention to bundle sizes is most important. For example, for our 10GXS cable, the maximum bundle size is 150. If you’re not able to control bundle sizes or you’re not sure how large bundles will be, then it might be worthwhile to deploy LP cable. Underwriters Laboratories developed a Limited Power (LP) certification, which verifies that a cable has been evaluated to carry the marked current “under reasonable worst-case installation scenarios without exceeding the temperature rating of the cable.” This is achieved by manufacturing the cable with insulating and jacketing material that can handle higher temperatures.

Straka: In general, using Category 6A 23-AWG cables with a cable operating temperature of 90 deg. C means that one does not need to concern oneself with bundle sizes on the bulk cable. As long as the cable is installed in a location with an ambient temperature at 45 deg. C or lower, the cable will not exceed the operating temperature in any practical environment. In using smaller-gauge cables like 28-AWG patch cords, it is recommended to limit the cable bundle sizes if all cables will be running IEEE 802.3bt at the highest power levels.

Q: What testing requirements or recommendations should installers and cabling-system end users be aware of and/or implement?

Mullins: For cabling installers, IEEE PoE standards include specifications for resistance of the cabling—not just the amount, but the difference between pairs and each conductor within the pair (typically called “balance”). Resistance problems can lead to lack of power and communications failures. Similar requirements were adopted in TIA and ISO cabling specifications, but because field testers could not measure these parameters, the related testing standards do not require resistance testing. Because installation techniques can impact these measurements, field testing makes sense. Now that field testers can make these measurements quickly and easily, we recommend that installers perform them on any cable that could potentially carry PoE.

For integrators installing PoE equipment, having a tool that can quickly identify the presence and amount of available power on the cable can save a lot of time trying to troubleshoot if the problem is in the switch, cabling, or device. In many cases, the integrator may not have access to the switch to determine the amount of power (if any) that is being supplied.

Tellas: The field test of the channel is most important. Even though it’s not required per standards, it’s also wise to check cable resistance to make sure it’s within the limits. At room temperature, the maximum resistance is 25Ω across all temperature ratings.

Tremblay: The Ethernet Alliance members recognized the growing concerns of PoE interoperability issues arising between PSE and PD. The solution was made available with the Gen 1 and Gen 2 Ethernet Alliance PoE certification program that subjects PSE and PD products to a rigorous test plan based on IEEE 802.3 PoE standards ensuring reliable multivendor interoperability. Approved PSE and PD products are listed on a public registry for easy searching. Gen 1 “EA Certified” or Gen 2 “EA Certified 2.0” PSE and PD logos are also placed on the product, packaging, and documentation providing a clear visual indication of certified PoE products.

Jones: I think it is important to point out that this Ethernet Alliance PoE logo program was written by the same team that wrote the IEEE 802.3bt specification. The group covered all the typical interoperability issues to ensure that a logo product will have a high level of confidence of interoperability with other logo products.

As far as cabling system testing, they should continue the testing that is currently done. It’s important to know the channel resistance complies for efficient PoE delivery and of course the other data-specific parameters.

Straka: DC resistance unbalance both within a pair and between pairs is a key specification for the next generation of PoE. DC resistance unbalance within a pair means that the resistance of each wire within a twisted pair should be very similar. DC resistance unbalance between pairs means that the resistance of each of the four pairs should be very similar.

Items that can affect this are cable construction and design, the quality of jack terminations, and plug terminations within a patch cord. Using cabling and connectors from well-established vendors and installers can ensure that your products perform as required.

Verify that the testing tools being used are capable of testing for these parameters and that the settings being used allow for the testing of them.

Q: The term “Power over Ethernet” is included in the title of the IEEE’s 802.3bt standard. But PoE is not the only technology ecosystem that enables the delivery of power to network devices via data cabling. Can you discuss other forms or remote power delivery and some of the applications for which they are commonly used?

Ensign: PoE is power with Ethernet, and the ability to deliver both over one cable. It will only work with an Ethernet connection with the device, and will not transmit power without it. There are other applications that only need power and do not need Ethernet, which digital electricity (DE) is a great application to support. DE has the ability to deliver power over structured cabling or low-voltage cabling at extended distances with the output being AC or DC power.

When considering power, it all comes down to DC power, which can be delivered via PoE or DE with the power limits set for them at set distances. Here are some good applications for DE, which can be AC or DC related: powering up PoE sourcing equipment; powering low-voltage applications that do not require Ethernet, such as USB charging outlets, small motors such as shades, TVs and more; providing power longer distances of 3000 feet plus; using hybrid cables (copper conductors for power and singlemode fiber all under the same jacket) for remote or longer distances.

For DE structured cabling is the medium. 22-AWG Category 5e, 6, or 6A would work, but to get the best distance and power performance, 18 AWG is recommended. This would be more of a control cable. A new, upcoming trend is to use renewable power, taking that power directly into the PoE sourcing equipment, then delivering DC all the way to the end device with no conversion to AC. This would offer the best efficiency.

Straka: Power over Ethernet is standards-based and is the most common approach to provide power and data via data cabling. In general, Panduit recommends using PoE for most data and power applications. There are other approaches that exist in the market, such as power delivery over a hybrid fiber and copper cable that can enable power delivery beyond 100 meters. This can be useful for applications in areas like outdoor cameras where deployments may be further than 100 meters from the nearest switch. Typically, these devices require media converters where a transmitter converts a copper signal to transmit over the fiber and a receiver that converts the fiber signal back into copper.

There is also a unique technology that is seeing larger adoption, called digital electricity. This technology sends power via pulses and has found a niche with distributed antenna deployments. It is viewed as a very safe and low-cost way to deploy power to the different DAS components.

There is a new technology being developed called Single Pair Ethernet that will offer both power and data over a single twisted pair at lengths of up to 1000 meters. While the data rates and power delivery will be lower than traditional Power over Ethernet (10 Mbits/sec at 7W and 1000 meters) it is believed that they will be sufficient for many applications like sensors and cameras.

Tremblay: The term PoE refers to IEEE 802.3 PoE standards which include Clause 33 titled Power over Ethernet over 2-Pairs (i.e. IEEE 802.3af and IEEE 802.3at) and Clause 145 titled Power over Ethernet (i.e. IEEE 802.3bt). All other remote power delivery methods are typically engineered systems providing unique power technologies tailored to the desired applications which may or may not interoperate with PoE products designed to IEEE 802.3 standards.

Standardized PoE is also extending to new and emerging ecosystems supporting IEEE 802.3cg Single Pair Ethernet which utilizes a different cable model than traditional 4-pair Category cabling. The Single Pair PoE applications include industrial automation, transportation, and building automation supporting power delivery for intelligent lighting, elevators, and HVAC systems to name just a few examples of remote powered devices.

Jones: There are a number of application-specific solutions for remote power delivery, but none of them approach the breadth of application space successfully served by IEEE 802.3 PoE. I am not aware of any other standards specifying delivery of power to network devices via data cabling. Anything that delivers power to network devices that doesn’t comply to IEEE 802.3 likely blindly places power on the cable. That is a bad idea in my opinion.

Tellas: Using data cabling to deliver power is not a new concept. Within the NEC are provisions for Class 2 and Class 3 circuits that use data cabling to deliver power for items such as control circuits, door openers, home theater systems and fire and security systems. HDBaseT also has its own version of power delivery called Power over HDBaseT (PoH). Devices that use RS-485 protocol often use Category cabling to deliver power and serial communications. The list of items is endless and delivery of power using data cabling has been—and will be—with us for quite some time.      u

Patrick McLaughlin is our chief editor.

Power over Ethernet simplified

Power over Ethernet (PoE) is a long-established, well-adopted power delivery technology that injects power over 100 meters of standard Ethernet cable defined in IEEE 802.3 standards. It radically simplifies installation for traditional end equipment such as IP phones, wireless access points, and IP cameras. With increased power delivery up to 90W, new PoE end equipment like intrusion control panels, advanced occupancy detection, industrial lighting, medical devices, professional AV equipment, and digital signage are taking advantage of standardized PoE benefits.

As PoE installations proliferate, so have the range of PoE-capable devices using different brand names and terminology. With no visible way to distinguish between standardized and non-standardized solutions, interoperability issues and market confusion have resulted. The Ethernet Alliance, a global consortium dedicated to market education and advancement of Ethernet technologies, has introduced the Ethernet Alliance PoE Certification Program to distinguish PoE standards-compliant products from proprietary Power over Ethernet implementations. Its goal is to improve end-user experience by vastly improving interoperability and eliminating market confusion.