Power over ethernet (PoE) technology allows electrical power for lighting, HVAC and security systems to flow over an ethernet cable rather than standard electrical wiring.
PoE simplifies cabling because only one cable is needed to provide electrical power and other applications to devices in a local area network (LAN) system.
Mark Mullins, marketing manager for Fluke Networks, Everett, Wash., said PoE use is expected to increase more than 12% over the next four years because it makes installation of devices such as security cameras and access points simpler.
“However, a survey by the Ethernet Alliance of over 800 installers, integrators and end-users found that four of five respondents experienced difficulties in integrating PoE systems. Part of this can be traced to the fact that the IEEE offers three PoE standards,” he said.
Mullins said there are three levels of testing that a PoE tester provides.
- The tester can determine the type and amount of power being offered by the power sourcing equipment (PSE), typically a switch or midspan power injector.
- The tester can request power at various levels to determine if the PSE can source the requested power.
- The tester can place a load on the PSE to determine if the voltage will be adequate when loaded. This is to determine if the PSE and connected cable can deliver the requested power level.
“Installing or troubleshooting PoE devices can be frustrating and time-consuming without being able to determine what is going on,” Mullins said. “Most of the time, installers don’t have access to the PSE to see what level or type of power is available, and even then, it may be a 300-foot walk to get there.”
After voltage and power, he said a device that can test cabling is very helpful.
“In many cases, a too-long or low-performing cable will cause a PoE device to fail or work poorly,” he said. “Second, look for testers that have been certified by the Ethernet Alliance for reliable multiple vendor interoperability. Third, basic network tests can ensure that the PoE device will be able to communicate with the appropriate network devices. It’s not much good if the device functions perfectly, but data can’t get to or from it because it is on the wrong VLAN or its IP address is incorrect.”
Mullins said Fluke’s MicroScanner PoE Cable Verifier and the LinkIQ cable+network tester are Ethernet Alliance certified for IEEE-Std 802.3af/at/bt. Some testers, he said, don’t support the latest 90W installations.
“Fluke recommends that the cable be certified to meet the appropriate requirements for resistance when it is first installed. However, certifiers are much more costly than the PoE testers discussed here and are best reserved for a dedicated product,” he said.
Lisa Schwartz, director of business development and product marketing at AEM Precision Cable Test, Chandler, Ariz., said as buildings become smarter, having devices in a LAN powered by PoE optimizes operations and maintenance while reducing the carbon footprint.
AEM Network Service Assistant
“There are different products out there that make varying depths of PoE testing,” she said. “We believe there are key components to the measurements they must have, in order to get a complete picture of PoE.”
Schwartz said testers should be able to:
- Emulate the end device requiring power by plugging into the network in place of that end device and telling the tester what level of power is needed. In doing so, the tester will now communicate with the PSE.
- Confirm if a PSE is present. (It happens; sometimes a device requiring PoE is plugged into a standard switch.)
- Measure available voltage, PSE type, PD class, PoE cable pairs in use and allocated power that the switch should be able to provide, based on the 802.3 or UPoE standard selected.
- Perform an actual load test, whereby the needed level of power from the PSE based on the standard selected and the tester reports back what is truly available at the jack. Results should be reported in voltage, current and wattage, all in “real power.”
“These are important measurements to be able to make when a device doesn’t turn up, to be able to test to see if the problem is maybe that the PSE is over provisions, not configured properly, [or if ] the device plugged into a switch is capable of providing power,” Schwartz said.
“Having test equipment that can perform this level of in-depth PoE testing is key to understanding a problem domain fast. In our case, our test equipment also has the ability to test the physical cable itself as well to ensure that isn’t the potential cause of the issue,” she said.
Schwartz said AEM’s TestPro multifunction cable tester and service assistant provides a packed set of cable testing and wired and wireless network testing, along with the most in-depth suite of test capabilities of any PoE test equipment.
Dan Barrera, director of product innovation at Trend Networks, Rockaway, N.J., said PoE-powered devices are coming to market that can make use of the full 90W of power that PoE can provide at the switch or up to 73W to a device at the end of a link. Integrators need to ensure that the installed network can support these new high-powered devices and systems.
PoE testers fall into three categories.
“The basic type can detect the presence of PoE on a twisted pair cable, but not identify the type or capabilities of the PoE system,” Barrera said. “Think of this as the equivalent of using a voltage detection pen on an electrical circuit. It will tell you that a voltage is present, but not much more.
“Intermediate PoE testers will provide some information about the classification of the PoE supply power sourcing equipment. There are nine PoE classes ranging from 0 to 9, each with different power capabilities. A tester with PoE class detection might tell you whether the system is 2-pair or 4-pair PoE, or which class is available. This tester might provide the voltage available on each pair to a PoE device, and while helpful, it can be misleading.
“The last type of PoE tester will negotiate with the PSE to determine the highest class it supports, and then it will simulate a PoE device by placing a load on the line to determine how much power is available during operation. This will provide the user with a voltage and wattage measurement so they can be certain that the circuit will support the devices that are intended to operate on it. Think of this type of tester as a battery tester that puts a load on the battery and measures the voltage and amperage delivered under load to provide a true measurement of the battery’s capability.”
Barrera said a PoE tester that loads the circuit will tell the user the voltage and current delivered to the device, which is reported as watts. The ability to load the circuit can be used to quickly determine if an installed cable will work with the intended application, and if not, whether the problem is with the cabling or the PSE.
“If a test fails to provide the expected wattage at the PoE device location, the technician can troubleshoot by repeating the test while connected directly to the PSE/switch,” Barrera said. “If the test fails again, troubleshooting can commence on the network side of things. The switch port could be set to a power-restricted mode, or it could be over-subscribed, meaning it is delivering the maximum total power for all ports combined. If the test at the switch port passes, it can be assumed that the cabling is limiting power to the device.”
PoE standards are based on 100 m/328-foot channels of 24 AWG category 5e or better. A 24 AWG pure copper cable may be able to operate at 125 m or 130 m and still provide full power.
However, several companies are marketing cabling systems that can reach more than 200 m/650 feet, specifically for PoE applications with the intent of reducing system costs by providing long-reach links without the need for additional telecom rooms to repeat/boost signals. Long-reach links are typically constructed of 23 or 22 AWG cable to reduce DC resistance and voltage drop.
At the opposite end of the spectrum, installers need to be aware of low-cost copper-clad aluminum (CCA) network cable. CCA cable is constructed from aluminum conductors with a thin layer of copper coating. CCA cable supports data relatively well because the high-frequency signals travel on the outside copper skin of the cable with little resistance. On the other hand, DC current travels through the center of the conductor and the aluminum has much more resistance than copper, limiting PoE distance.
A PoE load tester doesn’t know or care how long the cable is, or what it’s made of. It simply performs electrical measurements to inform the user of available power at the network device location.
There are a wide variety of testers available that include PoE testing functions.
Trend Networks PoE Pro tester
“The simplest is an LED that lights on a circuit, to testers that measure voltage on the pairs but don’t report watts. For example, Trend Networks’ VDV II Pro will detect PoE and show voltage, but it won’t perform a full PoE test,” Barrera said. “This might be fine for a technician who usually installs new cabling with occasional troubleshooting, but is not a good solution for someone who needs to verify PoE compliance.”
Header image: Fluke LinkIQ tester, www.flukenetworks.com