Knowledge is Power (...over Ethernet)

By Errol McCall, CXtec Product Engineer


Not all Power over Ethernet, or PoE, switches are created equal.

When it comes to evaluating a PoE solution for your network, there is a plethora of options at your disposal. It’s crucial that you do your research and plan accordingly for the types of devices that are currently on your network, the type of power these devices generate, and what they will require in the future.

PoE vs. PoE+

A PoE switch's maximum output is 15.4 watts per port. Then there are PoE+ switches that can generate 30 watts per port. The most recent version coming out, known as 4PPoE (4 Pair Power over Ethernet) can handle even higher wattages broken down into two new levels of power: 55 W (Level 3) and 90-100 W (Level 4).

To muddle the waters a bit more, a lot of switches are not even full PoE. Which means if you want to run the full 15.4 watts on every port, it may not have enough power. This is often done to keep the cost down because the network does not always call for PoE on every port.

The factor to pay attention to is how many watts of PoE the switch can handle. However, be careful when looking for this information. The “Maximum Power Rating” of a switch may say 480 watts but if you take a deeper look, you will find that PoE power is only 370 watts. This is because some of the power is used to run the switch outside of the PoE features.


Let’s break it down:

When you do the math on a 24-port switch you get:

15.4 W x 24 ports = 370 W

This will work, however, the power does not change when going to the 48-port version of the same switch family.

15.4 W x 48 ports = 740 W

On a 48-port switch you will only be able to do 24 ports of full PoE. 


This may seem like a bad thing but in most cases it's ok. The most important question to ask is, “What are you connecting to the switch and how many watts does it take to power it?” Networks rarely need full PoE on every port. Usually, they are just powering phones – the average phone only needs 3 to 7 watts.

If we go with the high number and use a 48-port switch with 370 watts of PoE, you get a switch that will be more than adequate to support your needs:

7 W x 48 ports = 336 W


But I need more power!

More power, you say? Do you have access points and IP cameras? These devices can pull anywhere from 7 watts to even more than the 15.4 watts of standard PoE. Again, the key is finding out how much power each device that you are plugging into the switch needs, then add it up. If it's lower than the PoE power the switch provides, then you have the right switch! If it’s not, then you will need an external power source to provide the switch with more power if it can except it. Or you will need a switch with a bigger power supply that provides the switch with more power for PoE.

Just like PoE switches, not all upgrades are created equal. Not all users need an upgrade, yet most will jump right into requesting a PoE+ switch that they don’t really need. Here the same problem exists. These switches can also be under-powered for full PoE+ on every port. Secondly, if you only have phones or other devices that do not go above 15.4 watts, then you can save a lot of money by just going with a standard PoE switch.

When to upgrade

In order to make a decision on which PoE switch is right for your network, simply start by asking yourself how many watts does each device you are connecting to the switch need? Does anything require more than 15.4 watts? Keep in mind that if you have even one device that will need more than 15.4 watts then the entire switch must be PoE+.

If you find that you are still uncertain which will work best with your existing network switches, work with a quality technology partner like CXtec. A knowledgeable partner can provide engineers who can help you through the power calculations (like above) to determine exactly what you need.

And a quality partner can supply you with PoE switches, PoE+ switches and can even offer chassis solutions that might combine both PoE and PoE+ into one switch for greater flexibility and cost savings.

With great power (…over Ethernet) comes great responsibility. 

Image courtesy of Pixabay