I'm living in a recently built apartment in Germany. There are many ethernet wall socket in each room. When connected my Macbook to the router directly with a cat 5e cable I can get around 800 mbps but I want to use the ethernet wall socket instead but it gives me only 100 mbps. Note that I have a gigabit contract. I'm using same 5e cat cable. My only theory is that the ethernet cable installed in the walls connected to the socket walls is causing the issue. But when I have opened it it seems like they are using cable cat 7. I have attached a screen shots of the socket. Do you have an idea what can be the issue ? or how can I investigate further ?

Update 1: I have tested all ethernet sockets of the apartment and I found that 3 of them are having issues but I was able to get the 800 mbps with the other wall sockets. Do you know what can be the issues with the 3 sockets that have a limited speed to 100mbps ?

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Update 2: Here is an example of a socket that is working fine:

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and the other end:

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  • One of the pairs that are only used with 1000Mbps Ethernet (pairs 4/5 and 7/8) could be damaged, broken or improperly connected. There are cheap UTP/STP cable testers available that can bring this to light.
    – StarCat
    Nov 11, 2020 at 13:23
  • @StarCat I have tested with another socket and there is no issue. It's this specific socket (and other two) that has a problem. Do you see something wrong in the photo or it's just an assumption ?
    – iOSGeek
    Nov 11, 2020 at 14:02
  • Is this tester enough to confirm that something wrong with the wall socket ? amazon.de/-/en/Network-tester-RJ11-Cable-Different-Selector/dp/…
    – iOSGeek
    Nov 11, 2020 at 14:08
  • I don’t see something in the photo that leads looks obviously wrong, except the fact that the cable seems slightly damaged and might have been bent in a small radius (but this does not look like a problem). The fact that 100Mbps seems to work but not 1000Mbps might be a that one or more pairs do not work, which can be easily tested. There might be other problems such as long cable lengths or improperly configured ports on the other side of the connection. Has the cabling installation been certified by the installer?
    – StarCat
    Nov 11, 2020 at 14:35
  • Are you 100% sure, it's not the LAN cable(s) itself? (Running from the socket to the PC?). We had similar issues in our newly wired office recently, and actually we had bad LAN cables. Once the bad ones were thrown out, all connections worked up to speed.
    – Marcel
    May 18, 2021 at 7:00

1 Answer 1


It seems that on some of the outlets not every wire is correctly connected.
Either a bad contact or 2 wires got swapped around. That can be in the outlet itself, or on the other end of the cables, which will be somewhere in the building close to were the router is located.

100 mb/s only uses 2 pairs of wires. 1000 mb/s needs all 4 pairs. If the installer of the cabling used a 100 mb/s only tester to check the lines when installing the outlets he/she may have missed bad connections on the pairs that are only used with 1000 mb/s connections.
I have seen that happen before... In new buildings, especially housing (instead of offices) a regular house-hold electrician usually also installs the data-cabling, often with only limited knowledge of the specifics of data-cabling.
It is quit possible the electrician didn't even know that his cable-tester wasn't suited for gigabit.

What you can try:

  • If this is a rental get the landlord involved. Don't mess with it yourself.
  • If you own the place: Check if you still have warranty from the builders and have them fix it. It isn't "fit for purpose".
  • Compare the bad outlets with a good one to make sure the cable-colors match. If the wires are in the wrong order you have to pull them out and re-seat them back into the clamps in the right order. You can use a small flat-bladed screwdriver to push the ends of the wires down into the clamps.
  • If they wires are in the right order you can also use the screwdriver to push the cable ends deeper in the clamps to make sure they make good contact.

There are specialized punch-tools to lock the wires into the clamps, but a flat screwdriver works in an emergency. Just use a small one. You don't want a too big blade to spread the clamps so far apart that loose their grip on the wire.

  • I am not familiar with the wall hardware, but typically, the middle two pairs are "shifted" and the photo looks like naive white+color pairing. it seems odd that twisted pairs need separation at the pins but it does have an impact, especially with more length. may not be fixable if the OP does not have access to both ends
    – Yorik
    Nov 11, 2020 at 15:22
  • @Yorik From the numbers on the clamps (87456321) the colors are correct for T568-A wiring, which also matches the A seen below the 12. Obviously both ends need to use the same ordering. Of course the white wire of each pair should go right next to the colored wire of each wire-pair. I can't tell from the photo if that is the case here.
    – Tonny
    Nov 11, 2020 at 15:48
  • @Yorik It doesn't matter if you use T568-A or T568-B as long as both ends of any given cable use the same variant.
    – Tonny
    Nov 11, 2020 at 15:50
  • OK, so the clamp terminals are in paired order but they handle the swap at the pins. I couldn't read the terminal numbers
    – Yorik
    Nov 11, 2020 at 15:51
  • @Yorik It is a fairly common construct on wall-outlets. Makes it easier/quicker to wire them up for the electricians if you don't have to split them too much. Also reduces the risk of splitting them over too large a distance.
    – Tonny
    Nov 11, 2020 at 16:10

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