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How to do an easy PoE test under 10 seconds

PoE (Power over Ethernet) has become such a commonplace technology that it is easy to take for granted. If we connect a phone, access point, security camera, card scanner, or other PoE-enabled device to a port that supports power, we expect to see lights and activity. Plug and play, right?

What happens though when there is a problem with PoE? Is enough power being sent to a given port to properly power a variety of end devices with different voltage requirements? Shouldn’t we test it just like we do the network before we connect devices that support business-critical applications and services?

How to do an easy PoE test?

In most environments, technicians “test” PoE by connecting the powered device (PD). If it powers up, they move on to the next connection. If not, they conclude that PoE doesn’t work and jump into the switch configuration. However, just because a device doesn’t light up doesn’t mean that PoE is disabled or not working at all. It may be that the link is simply not providing enough juice to power up the device.

It is up to the technician to troubleshoot whether there is a configuration problem in the switch, a cable issue, or if power is being sent at all. The first two things can be accomplished using a laptop (if it has an RJ45 port) and a basic cable tester. The latter though is a little more difficult. Most laptops and cable testers do not have the capability to test the actual voltage level being sent from a switch port to run a given powered device.

How to test PoE voltage?

The LinkSprinter is a pocket-sized tool that will tell you in 10 seconds if proper power is being provided (as well as thoroughly test the network link), and report the amount of voltage at the wall jack. Key point – The amount of power coming out of the switch port (the “PSE” or power sourcing equipment) itself will be stronger than the actual power at the wall jack where the powered device sits. This is because power will dissipate as it travels down the wire, and it is therefore essential that you test PoE voltage at the edge of the network where the powered device sits and not directly at the switch port.

You’re already plugged into the wall jack, so you might as well validate network connectivity while you are there… In addition to PoE testing, LinkSprinter’s automated test will allow you to identify cable faults or validate link speed, switch connectivity, DHCP auto-negotiation (can use a static IP address if needed), gateway availability, and ultimately, get to a target destination in the cloud such as www.google.com from that wall jack.

Additional points to consider:

  • LinkSprinter can run off PoE, so no need to worry about battery life.
  • Most access point connections are installed in or near ceilings, where it can be awkward (if not dangerous) to test with a laptop. The LinkSprinter fits easily into the palm of your hand, making it easy to slip into hard-to-test areas.

Common PoE issues to watch out for

It is important to watch out for a few common PoE issues:

  • PoE is subject to the same distance limitations as standard network cable runs – 100m/328ft
  • Incompatibility between powered device (PD) and power sourcing equipment (PSE)
  • Switch power budget over-subscribed
  • Switch provisioning of PoE
  • Power limited per port
  • Cable faults

When provisioning the switch for the various PoE devices it must provide power to, it is important to calculate the overall power requirement or “power budget” for all devices you are planning to connect to a given switch. The next step is to validate that the switch can provide that amount of power output to each device. It’s also a good idea to document what’s connected to each switch port to make troubleshooting easier as well as moves, adds, and changes down the road.

After each test, LinkSprinter automatically sends your test results to the free and included Link-Live collaboration, reporting, and analysis platform. You now have a documented record of connectivity from each wall jack, including switch slot/port/VLAN details. These test results can also be e-mailed to yourself or other team members so they can be viewed from any mobile device. You can reply to the e-mail and add comments from your mobile device with the wall jack location or other important information that helps you to identify the complete connection path. You can even attach photos to each test. This might include an image of the wall jack, of a connected device, or a serial number or asset tag.

Link-Live Results Report

LinkSprinter makes problem isolation simple

Instead of guessing at the issue when the lights on a PoE powered device are dark, technicians can test and validate PoE before connecting phones, access points, or anything else that runs on this amazing, simple, and critical technology.

Note: If more detailed PoE testing is required, consider LinkRunner AT. LinkRunner AT not only reports the level of voltage at the wall jack, but also reports on what class of PoE is configured and is capable of drawing a 25W load – what we call the TruePower™ test – to measure power, not just voltage.

Download our PoE Reference poster as a quick guide for powered devices.

Author Bio –
Product Manager – Wireless

Julio Petrovitch is a product manager at NetAlly, plus a certified CWNA/CWAP/CWDP/CWSP. He’s worked with network design, testing and validation for more than 15 years. Throughout he’s career he has had the opportunity to work with multiple networking technologies, including POTS, DSL, Copper/Fiber Ethernet, Wi-Fi, Bluetooth, and BLE.