What is POE?- Power Over Ethernet Technology Explained

In this blog, we will learn “what is Power over Ethernet Technology?”, which is also commonly known as PoE. And we will also see some standards which are used for this Power over Ethernet technology.


Now, as we know, Ethernet is the networking protocol that is used to establish the local area network or LAN, And data is carried using the network cables or Ethernet cables.

power over ethernet technology

What is POE or Power Over Ethernet?


Now, in PoE or Power over Ethernet Technology, along with the data, power can also be carried on these ethernet cables. And using this, the different network devices can be powered up.


Generally, the network devices which require less power are powered up using this power over ethernet technology.


So, the IP phone, wireless routers, and IP cameras are examples of the network devices which can be powered up using this power over ethernet technology.


And today if you see, this power over ethernet technology is so established that millions of devices in the world are powered up using this technology.


Now, there are several advantages of using this power over ethernet technology.


Advantages of Power Over Ethernet Technology:


  1. You don’t require additional wires to power up these network devices.


  1. You can also install these network devices in inaccessible locations where it is difficult to provide the power supply. 


So, using this power over ethernet technology, it is possible to maximize the saving on the installation cost.


Techniques used in this POE Technology:


Now, there are several techniques for transferring the power over these Ethernet cables, which are defined under some IEEE standards.


And here is the list of IEEE standards, which are commonly used for transferring the power over these ethernet cables.

power over ethernet standards

Now, under these standards, several things are defined. Like, how much maximum power can be transferred over ethernet cables, what should be the length of the cable over which we can safely transfer the data, or what should be the maximum voltage or current which can be applied over these ethernet cables.


So, before we see these standards, let’s, first of all, understand some basic POE terminologies.


POE Terminologies:

So, the equipment which supplies power to the network devices is known as the Power Source Equipment or PSE.


And the network devices which receive power over these ethernet cables are known as the Powered Devices.


So, now before supplying the power to the network devices, the first thing PSE checks is whether these devices are PoE enabled or not?


And to check that This PSE sends signals in the form of voltage to these Powered devices. And in response, it receives the signature of these powered devices, which is nothing but the resistance across this Powered Device.


Now, every powered device has some internal resistance that is isolated from the main circuitry.


And once the signature detection procedure gets completed, and if the powered device is eligible to receive power from the PSE, the actual circuit will get exposed to the Power Source Equipment.


So, now the resistance that is detected by this PSE is in the range of 19 Kilo ohm and 25-kilo ohm, then this powered device is eligible to receive power from this Power Source Equipment.


And if this resistance is less than 15-kilo ohm or greater than 33-kilo ohm, then this PSE will not supply power to this powered device. That means this powered device is not eligible to receive the power from the power source equipment.


So, now this entire signaling procedure for detecting the resistance across this powered device is known as resistive power discovery. Now, the entire signaling procedure is defined under this IEEE 802.3.af standard.


So, now once this procedure gets completed, the PSE finds out how much power is required by the powered device. And to find that it applies the specific voltage to the powered device. And in the response, it receives the current that is flowing through this powered device.


So, in this way, the power source equipment decides, how much power should get supplied to this powered device. So, under IEEE 802.3.af , the maximum power which can be supplied by this PSE is 15.4W, and the maximum power which can be received by the powered device is 12.95W.


And obviously, the received power will be less compared to the supplied power because some of the power will get lost across the cable resistance.


So, now let’s find out how this PoE-enabled network switch is connected to the powered devices, like IP cameras using this ethernet cable.


So, now if the network switch is PoE enabled, then we can directly connect this power source equipment with this powered device like an IP camera.


So, if the switch is not PoE enabled or in other words, it can not supply power to the powered devices, then you will require another device which is known as the Midspan. So, this Midspan adds the PoE capability to the standard networking switch.


And if you see the wiring arrangement of the ethernet cable, it will look like this. So, the data pairs will go as it is and power is supplied by this Midspan over the spare pairs.


So, now if you don’t know about the ethernet cable wiring the ethernet cable has 8 numbers wires. And under the 10 base T and 100 base T network, out of these 8 wires, only 4 wires or two twisted pairs are used for the data communication and 4 wires remain as spare.


While in the case of 1000 base T network or Gigabit ethernet network, all the four pairs are used for the data communication. 

poe applications

So, now there are two possibilities or two different types in which we can provide the power over this ethernet cable.


The first method is known as Type- B or alternative B method. In which power is supplied over the spare pairs of this ethernet cable. 


While in the case of Type A or alternative A method, power is supplied on the same pairs over which the data is carried.


And this technique is known as the phantom power feed technique.


So, now as I said earlier, three different standards exist for this power over ethernet technology.


So, now we have already discussed this first standard. That is IEEE 802.3.af, over which the maximum power which can be supplied by the PSE is 15.4 W. 


While if you see the second standard, which is also known as the PoE +, over which the maximum power which can be supplied by the PSE equipment is 30 W. 


While if you see the third standard, the third standard can support up to a maximum of 100 W of power at the PSE end. But this standard is still in the development phase. And this standard can be used for the Gigabit Ethernet network.


So, as I said earlier, in the Gigabit Ethernet, all four pairs are used for the data transmission. So, under this standard, the power will be carried on all four pairs of the ethernet cable, and as all the four pairs are used for the power transfer the maximum power which can be delivered across the power devices will be also more.


So, now once the devices over this standard will be commercially available, we can use them to power up not only IP cameras but even the LED bulbs at our house or at our offices.


Ir maybe it can be used to power up the POS terminals at the billing counters of the shopping malls.


So, these are the different classes of power that are supported by these three different standards. And according to the standard that is supported by these powered devices, these powered devices are classified under four different types.


And here is the complete list of the different properties of each standard. Like what should be the maximum voltage, what should be the maximum current, what should be the maximum cable resistance, and many other things under the particular standard.


So, I hope in this article, you understood what is power over ethernet technology.

If you want to know more about PoE technology, then visit the Wikipedia page

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