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Avoiding Common Issues with Power Over Ethernet

Power over Ethernet (PoE) has become a critical technology in today’s enterprise environments. It feeds power to wireless access points, VoIP phones, IP cameras, and an expanding list of IoT devices such as digital signage, wall clocks, thin clients, various sensors, building access controls, and even LED lighting.

As the demand for power to these endpoints has grown, the standards defining PoE have continued to evolve to support the increase. The latest standard, 802.3bt can provide devices with up to 71W of power over Cat5 cabling at lower speeds (up to 1Gbps), or Cat6a at higher speeds, which is enough juice to light up monitors and even laptops. IT is now no longer just in the business of delivering data, but also power to end devices.

Before we go too crazy with providing high-power connectivity to endpoints, it is important to validate the present infrastructure and cabling to ensure that the end device can get the power it needs. In many environments, a rudimentary PoE test is performed during deployment, consisting of connecting a low-power device and watching for the lights to turn on. After this, the link is generally considered “tested”. While this method may seem fool-proof, it often does not fully test the power provided on that connection, especially on links that may eventually support higher powered devices.

In addition to validating the power provided by the PoE system, engineers need to watch out for some common issues that impact a successful rollout of PoE.

Some of the most common PoE issues include:

1. Cable type. Ensuring high-power to end devices requires an end-to-end cabling infrastructure of at least CAT5 or higher. In fact, at some speeds like 10Gbps, an even higher cabling standard is required.

2. Cable faults. Lower-speed Ethernet connections can still continue to function even with some cable problems, such as split pairs or exceeded length. But PoE will often fail in these conditions. Any cabling issues such as shorts, opens, crossed and split pairs should be repaired before the link is used for PoE.

3. Misconfigured Power Sourcing Equipment (PSE). Make sure the configuration of the switch or mid-span injector is correct before connecting the cabling.

4. Incompatible technologies. Not all PoE versions and systems work well together, especially in a multi-vendor environment.

5. Vendor specific vs standards compliant. Some vendors have designed their own PoE methods to deliver power to their powered devices. Before purchasing a powered device, ensure that it supports the 802.3 PoE standards and not just the vendor method.

6. Exceeding switch PoE budget. Especially in higher-power PoE environments, it is easy to hit the switch-side power budget. We usually cannot provide power to every LCD screen on the floor from a single switch!

These issues can all be eliminated during rollout of the PoE network. Having a proper tool for testing PoE before deployment can go a long way in validating connections before they are used to power end devices. The LinkRunner G2 is a highly portable tool that can measure the power and data capabilities of a connection while installing or troubleshooting. The TruePower™ feature (pictured above) applies a load equivalent to the selected class in order to mimic a Powered Device. For more information on the LinkRunner G2 and TruePower, check it out below.


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