In 2018, the IEEE 802.3bt (PoE++) standard for Power Over Ethernet was approved. It offered more power, allowing devices like high-powered security cameras to be run on PoE. Which is great – until the installer uses the wrong cable to connect a camera and can’t figure out why it won’t power on.
Having multiple standards makes
troubleshooting PoE issues more complicated. For example, many field technicians
or network engineers don’t realize that upgrading to new pan-tilt-zoom cameras
or to Wi-Fi 7 access points with multiple radios will require a PoE upgrade as
well. As offices and warehouses deploy more smart devices that need PoE++, testing
becomes more important. This article will explain the PoE++ standard, best
practices in PoE deployment and testing, and how to solve several common
problems.
What
is the PoE++ Standard?
PoE++ is a Power Over Ethernet standard that provides more power -
enough to run high-performance Wi-Fi 6E/7 APs, digital signage, smart building
gateways and managers, power-hungry security cameras, and even some laptops
(using PoE++ to USB-C converters). It is part of the IEEE 802.3bt standard approved
in 2018 and formally published in 2019.
Here are the four types of PoE and the wattage they deliver:
● Type 1 (IEEE 802.3af): Delivers up to 15.4W.
Sufficient for basic VoIP phones and simple sensors. Not sufficient for most
modern devices.
● Type 2 (IEEE 802.3at / PoE+): Delivers up to 30W. The
standard for Wi-Fi 5/6 access points, VoIP and video phones, most IoT sensors,
and some cameras. It uses two twisted pairs in the Ethernet cable.
● Type 3 (IEEE 802.3bt / PoE++): Delivers up to 60W. It uses all
four twisted pairs in the Ethernet cable.
● Type 4 (IEEE 802.3bt / PoE++): Delivers up to 90W. It uses all
four twisted pairs in the Ethernet cable.
Common Causes for PoE++ Problems
Here are the four most common causes
of PoE++ problems. There are other possible causes, like a misconfigured power
sourcing device or using the wrong port. Still, if the device is plugged into
the right port but not working, one of these is often the culprit.
1. Powered
Device and Power Source incompatible: Many organizations using PoE++ still
use PoE+ and/or PoE as well. This mix of standards means not all devices can be
powered by all power sources. Older PoE or PoE+ switches cannot power newer
PoE++ devices. This is why those new Wi-Fi 7 access points won't run off your
existing PoE infrastructure (unless it was updated recently). Make sure you
account for this when planning to deploy new devices!
PoE standards are
backward compatible, so a modern PoE++ switch can power older PoE+ device, for
example. The switch and device negotiate the correct power level, so there’s no
risk of damage.
2. Wrong
cable type: PoE+ and PoE++ standards require the correct cables. For PoE+
(30W), Cat6 is the recommended professional baseline for
reliability. For PoE++ (60W and up), Cat6A is recommended. Using
undersized cables is actually a fire hazard because of the heat involved.
Pushing 60 or 90 watts through a cable generates a significant thermal load.
The thicker copper conductors in Cat6A have lower resistance, which means they
generate less heat and can handle the thermal stress far better than Cat5e or
Cat6.
Using cheap cables like
copper-clad aluminum (CCA) will also cause excessive voltage drops. This is
often seen in projects where CCA is used to save on costs.
3. Bad
cabling: If the cable itself is damaged the connected device may not work.
PoE++ uses all four twisted pairs in the cable, so opens, shorts, splits or
crossed pairs can cause the cable to not deliver enough power. Unbalanced cable
pairs or a bad punch-down when the cable was installed can also cause problems.
Length is also a factor. The
max length for reliable data transmission and PoE delivery according to the Ethernet
cable standard is 100 meters (328 feet). However, pushing a cable past this
limit is possible when using PoE extenders or other proprietary solutions. If
you must use a cable longer than 100 meters, testing the actual wattage
available in real-world conditions is vital.
4. Exceeding
the power budget: Every PoE switch has a maximum wattage it can supply
across all ports. If the total power requirements for all devices connected to
the switch exceeds that budget, some devices won’t power on. This is a very
common issue in new deployments.
To prevent this, avoid maxing
out your PoE power budget. Your total device load should be no more than 75-80%
of the switch’s total budget. This allows for future growth and does not stress
the device.
Testing and Troubleshooting PoE++
Proper PoE testing is key to make
sure PoE++ devices work as intended. Just plugging in a device and seeing if
the LED comes on does not cut it! That will tell you if the device has power –
but if it doesn’t you have no information to diagnose the problem.
A good handheld PoE test tool should
allow you to measure voltage drops, actual power delivered and even show you the
cable pairs being used. Not only that, it should allow you to emulate any PoE class
in order to validate you can negotiate and draw the exact wattage your device
needs.
In conclusion, as devices demand more power, assumptions
that worked for PoE and PoE+ no longer hold. Understanding PoE++, and having
the right test tools to validate real-world performance, is no longer optional
if you want reliable, safe deployments.
Wireless Product Manager
