Poe over 2 pairs to olimex esp poe

I’ve searched quite a bit but I couldn’t find a final answer.
Is it possible to connect the olimex Poe esp module (or any other Poe device)to a fast Ethernet (4 wires, two twisted pairs) and have both, Ethernet connection and Poe?
I found out that the standard Poe uses only two wires, but I couldn’t finally find out if a fast Ethernet cable is sufficient for that.


You can go all the way to gigabit if you have the right Cat5e or 6a ,cables, here is one explanation:

Depends. With 802.3 compliant PoE, there are basically 3 ways to transfer power to your device: mode A, mode B and 4 pair. Mode A uses only 2 wire pairs, it sends the power over the same two pairs as the data. Mode B separates data and power, sending the power down the two unused spare pairs. Both mode A and B only support Fast Ethernet at 100mbps. 4 pair mode uses, as the name implies, all 4 pairs to send both power and data and supports Gbit Ethernet.

In your scenario you need mode A. The mode is selected by the PSE (power sourcing equipment, typically your PoE router or injector). The good news is that according to the standard, the powered device (your ESP PoE module) has to accept all modes. The bad news is that not all PSE will support all modes. You need to make sure that your PSE supports mode A. Many PoE switches do, but not all.

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@Kdem i am not aware of a 4 wire gigabit connection. I think your article also only refers to 4 pairs (8 wires). I was laying a new line but only could fit one cable through one hole. I want to use the 4 pairs for two separate connections including Poe. So a 8 wire solution is not possible for me.

@HeyImAlex thank you very much for your detailed explanation. That should do it.

I understand what you are trying do now, but I suggest you consider the following. IMHO it will be almost if not impossible to terminate your single cable(I am assuming you have at least a Cat 5 cable) to two rj45 connectors and maintain the standard required for fast Ethernet (100Mb/sec), or POE. It may work, it may not work reliably; I would recommend looking into a POE powered splitter/switch (sometimes called extenders) and use your single cable to feed both devices that way. Just my 2 cents…

Why wouldn’t it work? I don’t doubt you, but I simply want to know the reason.
It’s a Cat7. The problem is that the connection is in a remote area where to electricity plug is available… IF there were no complete disconnections, I still would be fine with 10 Mbit/s. I guess I just need to try. There’s no way of fitting another cable or even electricity line to that area.

The twisted pairs, wound at different pitches inside the cable help resist external noise and magnetic effects (EMI), and ensure balance. The speeds high speed Ethernet operate at require good cables and connectors, and there are a lot of factors, which may or may not matter. To maintain the standards the twists, spacing and any shielding needs to be maintained as close as possible and even into the connector. This will be impossible as you split the cable some cm from the rj45connectors. The equipment you are attaching to is a possible source of EMI, and the connection is right on it.

I suggested something like this, I am not recommending this exact one, as I have no experience with it:

Just that this should allow your one cable to feed 2 POE devices, and it is powered by the POE, no power plug required. You need to check the power levels needed from the all the POE devices, but at a glance it would work. If sharing the band width on your single cable poses an issue, your Cat 7 cable(properly terminated) can do gigabit, if you can find a splitter/switch that will do that
I have done exactly what you are trying to do (without POE), with mixed success, at high speeds I had problems with the split cable, but not always.

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You don’t need active repeaters or anything like this on 100mbit. This isn’t 10Gbit ethernet. I have several runs wired like what your are planning, for pretty much the same reason (can’t fit more cables through an existing conduit). They work perfectly fine, over large distances (100m and even above, violating the standard, but still working without any issues). I use them for IP cameras, so there’s constant data flow on both 2-pairs. There are no interference problems at all, I get the data rate I expect on both separate 100mbit connections. 100mbit is a lot more fault tolerant than higher data rates. You’ll be fine.

To separate them out, I use splicing boxes like these (sorry for the French Amazon link). And on the patch panel, I just use two adjadcent slots to wire a 100mbit 2-pair on each from a single cable.

Just make sure to use high quality CAT6/7 with full copper core wire. Not that copper clad aluminium crap that you find all over Amazon.

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@HeyImAlex Sounds very promising.
Yes my plan is similar. I thought of a regular dual network outlet/plug, divide the pairs and connect my patch cables there.
I will try it.

Thanks for your help

If at some point in the future you need full Gigabit support on that link, then you can always swap to all 4 pairs. I wouldn’t use a splitter like the one Kdem linked to, these are for extending the cable length more than anything else. I would use a full fledged managed switch that is both powered by PoE and offers PoE ports, like the Netgear GS105PE. These are called PoE pass-through switches.