PoE Connection degenerating

[Plermpel]

Hi guys,

 

I have a strange phenomenon. I installed two TP-Link PoE APs at a friends house about two years ago.

They worked flawless for almost the whole time. About three weeks ago he told me one of them stoped working, now the second one is stoped working.

Today I looked into it and found out the the connections are not working anymore, they show up as 10Mbit link and loose uplink constantly, I put the APs on a different cable now and they work flawless again.

How can that be? It looks like the cables or ports lost their conductivity.

Every other connection in the house is still fine only the two which used PoE seem to be degenerated.

[OddOod]

Have you inspected the runs? Maybe there has been some critter chewing away at it. Or if they're in high humidity environments they might have corroded.
Sometimes cables just die. The fact that it's not all the time is the surprising part to me. 
I just resolved some connectivity issues with my server by replacing the patch cable. 

[Plermpel]

4 minutes ago, OddOod said:

Have you inspected the runs? Maybe there has been some critter chewing away at it. Or if they're in high humidity environments they might have corroded.
Sometimes cables just die. The fact that it's not all the time is the surprising part to me. 
I just resolved some connectivity issues with my server by replacing the patch cable. 

The runs are embedded in concrete. It is all of the time, one went offline first and the second one a few weeks later, now both runs don't work at all anymore. The rack actually is in a little wet environment, I already suspected that but why only the PoE lines? Is there any good way I can keep moisture away from the copper wires in the patch field?

[OddOod]

6 minutes ago, Plermpel said:

The runs are embedded in concrete

Are they directly embedded or are they in conduit?

6 minutes ago, Plermpel said:

why only the PoE lines

At a guess because they are carrying power and that somehow accelerated the oxidation. 

7 minutes ago, Plermpel said:

Is there any good way I can keep moisture away from the copper wires in the patch field?

The best way would be to not have the rack there. If you can't manage that, you can reduce the humidity with a dehumidifier, but that's gonna be expensive to buy and expensive to run. You could try outdoor grade gear, that tends to be more resilient

[johnt]

What POE switch is it?

[Plermpel]

27 minutes ago, OddOod said:

Are they directly embedded or are they in conduit?

At a guess because they are carrying power and that somehow accelerated the oxidation. 

The best way would be to not have the rack there. If you can't manage that, you can reduce the humidity with a dehumidifier, but that's gonna be expensive to buy and expensive to run. You could try outdoor grade gear, that tends to be more resilient

In a conduit but the contractor messed up the formwork so it's impossible to pull new runs.

I was more thinking about some sort of goo to protect the contacts I have seen that on DSL lines 

23 minutes ago, johnt said:

What POE switch is it?

It's a QNAP QSW M2116P

[Kilrah]

Have you checked the connectors at both cable ends and in the devices for corrosion?

Might just be a matter of replacing the connectors.

[OddOod]

On 3/12/2026 at 12:47 PM, Plermpel said:

it's impossible to pull new runs

Wait, did they fill the conduit with foam or something?
 

 

On 3/12/2026 at 12:47 PM, Plermpel said:

goo to protect the contacts

Like conformal coating? Not sure if that would mess with the contacts, I would advise testing before deploying it
That being said, if you want to roll the dice and go OLD school, you could probably get away with smearing vaseline on the jacks. 
But the first thing to do would be grab a cheap cable tester and check if all the conductors are intact. If you've got a broken wire, no amount of jiggerypokery is gonna save you. Though.... if you have two cables in the conduit and you can find at least 8 conductors that are intact, you could probably frankenstein something to work
 

[DraconisMaximus]

On 3/12/2026 at 11:59 AM, Plermpel said:

I put the APs on a different cable now and they work flawless again.

How can that be? It looks like the cables or ports lost their conductivity.

Please clarify this. It sounds like you said they are working with different cables on different ports. Have you tried different cables on the same ports?

Switchports can fail too. What is the model of the PoE switch you are using? Does it have a management interface with diagnostics?

[OddOod]

@Plermpel

Okay, I'm deeply curious: which of my unhinged proposed solutions made you mark me as the solution?