PV DC power lines in parallel with PoE link

The PV array parameters are: 2S2P east-west orientation, the panels are 450Wp. The expected Vmp is around 80V the current will vary up to 20A.

I am planning to run a FTP and a UTP cables in the same duct together with the PV solar cables (6mm2). The total length would be around 20-25m.

The FTP will be used to power and run the data (Ethernet) to an IP camera via PoE and the UTP will be user for some sensors purposes. Should say that this will not be a ieee poe but a self made 12V DC over the unused ftp pairs which will power the IP camera on the roof, because it does not support the ieee poe standards.

Is there any potential for some issues either with the PV lines or with the PoE and data In terms of EM compatibility? Should I run them in separate ducts and if yes, is there some practical distance requirement? All is DC except ethernet data. The PV and PoE currents will flow in different direction if it matters as well.

Run the DC PV in a separate metal conduit/sprag.

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I agree with @_a_a_a , I have my DC PV running close to a analog camera line (by which I mean they pass next to each other) and there is clear distortion on the picture (but only during daytime). Keep them apart as much as you can.

Question: What’s an FTP cable?

I would assume that is for Foiled (also Shielded) Twisted Pair vs Unshielded (FTP/STP) Twisted Pair (UTP).
It would be confused with File Transfer Protocol (FTP) that is widely known. Must be why everyone moved to calling them CAT cables for their specification category.

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Aaah ok! Sorry about the dumb question, but I was wondering what File Transfer Protocol has to do with it :slight_smile:

(I’m getting old… I don’t think FTP is used as much for file sharing as it once was).

There is a lot of security risks these days with FTP, so most of it is moving the SFTP which is actually more related to SSH than the old FTP protocol ( SSH File Transfer Protocol).
The nice thing about that is that you don’t need to run a seperate FTP service as it all runs from the SSH service.

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Yes, I meant FTP as Foiled Twisted Pair cable. The foil helps eliminating some interference from outside.
My assumption was that the DC current from the PV could do some magnetic field which may cause issues with the ethernet communicaion (despite it is a digital coding underneath) and the 12V DC power line that will go over the spare pairs of the same FTP cable.

Thanks for the comments so far. If someone else has also done something similar, will worth sharing practical experience.

I have collected a bunch of fibre optic patch leads and will be available in standard lengths. I don’t know about the Tx/Rx gear but it surely is available. This would solve all interference issues…

The thing is - the cables from the PV is not purely DC, they can have significant ripple at higher frequencies.

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The problem with fibre optics is: they are notoriously difficult to use in applications where you have POE, like this one :crazy_face:


Beem me up Scotty!

If the magnetic field was simply constant or fluctuating slowly, it would be of no concern. Physics 101, the so-called right-hand rule. If the current flows in the direction of your thumb, there is a magnetic field around the conductor in the direction of the other four fingers. But if the current is constant, so is the magnetic field, and a constant magnetic field does not induce noise in other conductors. A fluctuating one does.

The trouble however, as @_a_a_a says, is that MPPTs create a significant amount of square-wave ripple at frequencies around 40khz t0 100khz, which is the typical switching frequencies of the buck converter inside, and that turns them into little radio antennas that can create noise in other conductors.

I can see that interference in an outdoor security camera of mine, which happens to use ethernet cabling for the connection. But I don’t know if it’s shielded cable. Camera and cabling came with the house…

What I can say is that your intuition, that you should probably not run them close together, is correct.

When you do run your FTP cable (separately), remember that you should only ground it on one side, otherwise you will create a ground loop. (Maybe not in this exact scenario, but definitely sometimes switch-to-switch.)

Easy way to do this is to use a metal connector at the switch side over the foil, and a plastic connector with the foil cut off on the far end.

Also make sure your switch is grounded – I’ve seen MANY shielded ethernet installations where only the cable <-> switch is connected, but then the switches aren’t grounded (different teams responsible :roll_eyes:). Most cheap ones are not (2-pin plug). The better ones have a grounding screw somewhere. Straight into the earth pin of a standard plug is fine.

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MPPTs need to be mounted close to the inverter for this reason :slight_smile: