Picture of Power Over Ethernet (PoE) Adapter

Power over Ethernet or PoE, is the technology used for power transmission in network equipment, via network UTP cable, together with data. PoE is useful in situations when we want to connect network devices that are far away from a power source. In this situation we take advantage of the Ethernet cable, because there are 4 pairs of wires, but for the majority of networks, only 2 pairs are used for data transmission. PoE uses 2 unused twisted pairs, for electrical transmission needed to power the device.

There are several architectures of PoE and many of them existed before the technology being standardized, due this fact not all types of PoE are compatible. PoE devices receive power directly from the network cable, but should be noted that according the manufacturers, specs like nominal values of voltage and current, and even pairs used to transport electrical energy may be different.

Source here.

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Applying a voltage across terminals not dimensioned for that, may damage the network device. To avoid this, the best way is to make a PoE adapter, separating the two input signals, via two simple circuits, an injector and a splitter. The injector will feed the network cable with power and this circuit is placed near the origin of the installation, where we have a modem or a switch, and of course a power plug. Then we have as outputs of the Ethernet cable, data and power that will connect to the device. Now we connect the splitter circuit, which receives data and power. From this circuit leaves an Ethernet cable and a DC plug avoiding applying unknown voltages to the devices.

As example consider the eLab case, which have a switch on the back of the room and we want to feed a 12V wireless router which is at the opposite end of the room, to obtain greater coverage by departmental area, in a place near a windows without power sources nearby. The network diagram is the one above.
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can I use only one wire for positive from 4 and 5?
same as one wire from 7 and 8? because in my lane cable two wire is not shown continuity means damage so I have only 6 wire.can I use POE protocol with 6 wire ?

eLab (author)  bhayanichirag7772 months ago

Hello. Well you can use only 6 wires, although the current for powering the device will be more limited. Usually we use 2 wires for positive and 2 wires for negative so it allows for less resistance in the wire, therefore less voltage drops. If you only use 6 wires, the resistance of the cable will be higher which translates to more voltage drops. What this means is that your maximum length of the cable must be much shorter.


I used 6 core from wire and my cable length is 10m and my internet is working.let's hope I will not face problem in future.

thanks guys this site is very useful....

eLab (author)  bhayanichirag7772 months ago

I'm glad it worked out! ;)

MikB2 years ago
If you are worried about voltage losses in longer cable runs (and you should be!) then certainly feeding a higher voltage and converting down remotely is a good idea.

Simple: 7805 or 7812 regulator to drop from a higher voltage. Gets warm, wastes power, current in (at say 15v) is same as current out to device.

Slightly Harder: Something like this http://www.ebay.co.uk/itm/140906034058 fitted at the remote end will take whatever's available from about 7v upward (this module goes to 24v) and transform it down to 5v.

It's a switching converter (buck converter) meaning it draws less current than the load. This is good. It reduces the losses in the wiring, and is even more efficient.

It's not exactly PoE standards compliant, it's not 48v, but it works.

I'm using some of those modules (and similar) to power remote IP cameras (draw 400-500ma, at 5v) from a centralised "injector" -- actually a hacked 8 port router with an extra PSU to give 15v on pins 4,5 and 7,8 on 7 of the ports (not the UPLINK port), just as shown here, but internal to the router

Each port can source 500ma (limited by it's own polyfuse), the load from a single camera is now down to around 280ma.

The voltage does drop too much to just feed 5v and hope for the best, especially on long runs.

eLab (author)  MikB3 months ago

Thanks! That is certainly a good idea.

AndyGadget2 years ago
Nice write-up with plenty of information and the appropriate warnings. I'll be using something similar to run a remote IP webcam. Be aware that in some countries 568A is the norm so check the connections carefully. (I love standards - There's always so many to choose from #;¬)
Curious, does the standard you choose really matter?
So long as you use the same pin out on both adapters it seems like the wire in the middle wouldn't matter all that much.
I took a short Leviton certification course 12 years ago, and if I remember correctly when making your cables you can choose either A or B, so long as you use the same one on both ends of the cable. (if you don't, you end up with a cross cable)

If this is incorrect then let me know, as I'd love to try this to free up an extension cord. :)
You are correct, you can go either way, but following the standard in your environment will make troubleshooting much easier. According to Comptia, two B ends would be used for a straight through cable. While two A ends would work as well, two B ends is the standard. If I were to find an A on one end, I would assume the cable is crossover; that is why following the standard is important.
eLab (author)  darman123 months ago

That is correct.

Plus, it is a good idea to stay in good practice whether it is in a department with other IT staff or it is in your own office/home.
eLab (author)  adillbeck3 months ago

Yes you're right, as long as you use the same standard in both ends, everything will work the same way.

One reason to be concerned with this is if you are working in a facility that requires a second party inspection of all work prior to being used. Granted in that case, this POE solution would not be expected to be used, but it's good to keep it in mind. It also needs to be kept in mind if you are going to be running this solution through a patch panel for facilities. Make sure that any ports that will be carrying voltage that is unusual for your facility is clearly marked.
eLab (author)  adillbeck2 years ago
As long as you use the same norm in both adapters, it's all fine ;)
You're absolutely right - As long as you're connecting the same both ends the standard won't matter. My comment was more of a 'heads up' in case anyone was using a mix of off-the-shelf components which could be marked differently.
(If you use anything other than one of the recognised standards, ensure the signal pairs are consistent otherwise the transmission characteristics would be affected.)
eLab (author)  AndyGadget3 months ago

Thank you!

eLab (author)  AndyGadget2 years ago
Thank you! We wanted to keep it simple but with all the necessary info.
miguipda2 years ago

here is a cheaper way : http://www.seeedstudio.com/depot/passive-poe-cable-set-p-1175.html?cPath=207

It's only cheaper if the power plug and jack are compatible with one's equipment. This Instructable shows you in a general way how to built injectors and splitters for virtually any situation.
eLab (author)  pcooper23 months ago

Yes, you're right :)

eLab (author)  miguipda3 months ago

There are lots of cheap devices everywhere. But the main goal of this post was to show everyone how simple it is to build a generic adapter, it's just contributing for the community knowledge and boosting the DIY culture.

Gadget932 years ago
This is a really cool and useful idea. As a CCNA and a CCDA I must mention though that due to the power and data running next to one another, there will be interference and noisy data. Alot of packets will be dropped and other problems will cause problems with data. Although if you don't have any other choice, go ahead...it is better than nothing.
stajp Gadget931 year ago
That's not the case if UTP is used. Even in CCNA learning literature there is an explanation why the UTP is twisted: to combat crosstalk. DC power, which doesn't change in regards to voltage or current, has minimal crosstalk to other twisted wires. The whole IEEE PoE standard takes a lot of consideration for optimizing this idea (and Cisco has PoE devices done according to standard), but there are similar projects to this which are used for years without any noticeable loss in data.

The only problem here is the quality of work when it's made and used. If it's done badly, then don't expect miracles, and crosstalk and other problems would arise :D
eLab (author)  stajp3 months ago

You're quite right! There are commercial devices already with built-in PoE. But the way it's done should be the main cause of success or failure.

eLab (author)  Gadget933 months ago

In any kind of situation there will eventually be lost packages, but the networking protocols are also designed to handle those situations. But for as far as we have tested this montage, everything has worked perfectly.

Good Afternoon From UK, Linda. I have a query, although I am no technical wizard, but is there no danger of this device generating Radio frequency interference, given that the cables over which the power travels may act as an antenna. This has happened many times here in UK, Europe and North and South America. I am not saying this WILL happen, only quoting the experience of what is called Power Line Transmission devices, which uses power cables to pass data between distant points in the same building. You are to be praised for your efforts posting, and this is a genuine concerned enquiry. Thanks for youre time, Best Regards, Gary
It is sending low voltage, low amperage voltage over a data line. It is NOT the same as data over power line, PLT, as the cable is made for data.

I use a similar set up in my shack with no RF problems at all.
eLab (author)  MW0GKX3 months ago

You're right.

We also have been using this for over 4 years now, and it has worked without any problems.

whitewolf, I believe that the problems with Power Line Transmission devices that you are referring to have to do with sending (analog or digital) signals over building mains wiring—AC powerlines—as with X10 and other devices or protocols.
eLab (author)  skinny*k3 months ago

Yeah, after reading your comment I realized the same thing. PLC devices are not the same as PoE devices, so there might have been a confusion in whitewolf comment.

eLab (author)  whitewolf4992 years ago
Thank you! Well, that is a common concern about PoE adapters but Ethernet communication is "kind of immune" to this type of electromagnetic radiation, besides the power lines being used in these cases are very low power. Therefore using some wires for power and some wires for data in the same cable, should not affect the transmission of data packets or the speed itself.
GregS2 eLab1 year ago

The power on the ethernet wires is not your power company's grid power, but the power coming from a power adapter. The power adapters are usually a DC output and as such have filter capacitors to stabilize the power they provide. Due to this, the power adapter would have the side-effect of low-pass filtering out any back-fed RFI and preventing it from entering the power grid.

eLab (author)  GregS23 months ago

Sure, the power adapters are usually well design to prevent those situations.

maestro_au eLab2 years ago
I'd add two more reasons - twisted pairs used in ethernet cable (and phone lines) are paired & twisted in an effort to minimise radiation/induction with an AC / RF signal on the wire.

PoE is DC and tends towards embedded devices with a steady current draw, therefore limited scope for radiation even from a straight wire conductor.
That is a good point. Also note that the use of STP (shielded twisted pair) network cables rather than UTP (unshielded twisted pair) network cables will reduce the likelihood of interference.
eLab (author)  darman123 months ago

Yes, higher category cables should always help to reduce interference.

eLab (author)  maestro_au3 months ago

You're absolutely right!

eLab (author)  whitewolf4993 months ago

I just realized you might be talking about PLC devices, or Power Line Communication, which uses the mains AC line as a mean to transfer data packages. That has nothing to do with PoE, and it does have its problems. PLC devices may cause many interference, noise among other problems. But it is completely different than what this instructable is about.

alleoOtechnoO6 months ago

Help me..

Tp-WA5210G received high ping, Some times the router page doesn't even load all the way or properly.

I'm use (PoE) Adapter for setup my Tplink WA5210G and different Lan Cable (Poe slot = Cat6 20meter) (Lan slot=Cat5e 1meter) is any speed effect on this case?

eLab (author)  alleoOtechnoO3 months ago

Hard to know :/

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