Damaged Cat 6 cable

[h0b0]

I have a cat 6 cable that goes through my walls and at some point it is damaged. Unfortunately, it’s the one that feeds my internet. It is also the most difficult for me to replace. Is there anyway of detecting where the damage is? I’m thinking something on the lines of my detector for the perimeter fence for my robot mower. That works like an AM radio.

The added challenge is that the symptoms of the issue are that my internet is down from 300mbs to 80mbs. So it’s unlikely there is obvious damage. Also, when I put plugs on the cable I used a tester that showed all cores connected. In a final act of desperation I replaced the plugs with wall sockets to test my ability to terminate and it wasn’t the plugs.

All this makes me think it’s unlikely to find a magic potion but after spending so much time converting from coax to Ethernet to move from 100mps to 300 and now ending at an unstable 80 is killing me.

[megaphone]

I would double check the terminations, if you are testing them correctly, all ends are good, then it probably won't be a damaged cable.

[Andeh1]

How are you testing the speed of it?

Have you a "known good" cat6 you can use to 'test the testers'.

Does it cross any major power cables? Does the cable run alongside any power cables?

Any other sources of major interference nearby?

Physically damaging the cable and yet it still working across all cores at 30% speed is unlikely IMO.

[peekay74]

Could cable be running too close to electrical wire ? Have heard this can affect performance over the Cat 5/6 cables ?

[anonymous-user]

Andeh1 said:

Physically damaging the cable and yet it still working across all cores at 30% speed is unlikely IMO.

^whs, they tend to either work or not work. If you’ve lost most of your internet speed, it’s probably something outside your property.

[essayer]

wormus said:

^whs, they tend to either work or not work. If you’ve lost most of your internet speed, it’s probably something outside your property.

Dropping to 80mbps makes me think it’s connecting with two pairs (100BASE-TX) instead of all four (1000BASE-T)
i.e. one of the pairs is damaged enough to pass a continuity test but not permit reliable comms

We had an alarm cable that had this, it ran under a beam and I think thermal expansion crushed it between the beam and the loft panelling, because it was totally stuck when I tried to pull it out.

Op have your tried different equipment at each end just to see if two other devices can negotiate at gigabit speeds? If not it might just be easier to run a new cable

[matt666]

If all 8 pins aren’t connected properly in the termination it causes those symptoms, it runs at 100Mb not gigabit. Also check the port on the device is gigabit and not 100Mb. Check with known good equipment until you narrow down the cause

[BobsPigeon]

You could hire a TDR cable tester (Time Domain Reflectometry) and test each of the 8 wires but even if you find an impedance break in one you'll need to rip it out so you might as well just pull it through with a new cable and save much time and money. That is if you're certain it's terminated correctly at both ends and isn't suffering cross talk (unlikely on CAT6 in a house) as suggested above.

[h0b0]

I have tested the internet speed by plugging a laptop directly into the ONT (sort of router on the outside of the house). It gives a stable 300. I then tested using the cable that goes into the house. That’s where I’m getting an unstable 80. Sometimes can be as low as 30 though.

I suspected the plugs because it’s cat 6 so changed the terminations first ton new plugs and then to sockets and used a pre-made cable on both ends. The results are the same.

As someone mentioned earlier up the page, the symptoms point to a damaged cable. Finding where it has been damaged may be impossible.

[Mr Pointy]

TDR testers are available for around £400:

https://www.idealnetworks.net/product/cable-verifi...
https://www.test-meter.co.uk/ideal-vdv-ii-pro-voic...

You might be able to hire a tester, but it would probably be one of the bigger Fluke models.

[h0b0]

Mr Pointy said:

TDR testers are available for around £400:

https://www.idealnetworks.net/product/cable-verifi...
https://www.test-meter.co.uk/ideal-vdv-ii-pro-voic...

You might be able to hire a tester, but it would probably be one of the bigger Fluke models.

Thank you for that. Once the snow here melts I will take a look at my options of running a new cable or fixing the existing.

[biggiles]

One cheaper option to check the pairs is to use an "ethernet splitter". As 100mbps Ethernet only uses 4 of the 8 wires, you can send two 100mbps ethernet signals down a single wire. You could use a pair of these to test one half of your wire, then the other half, which will tell you whether it's a wire problem.

The splitters are under a tenner for a pair.

Context: I have a very old long buried ethernet run which sometimes is dodgy - by using a splitter it's divided into two links, and normally only half drops out: so I have resiliency. This might be fine for you if your internet wasn't so speedy! But at least it may help you confirm the area of the problem.

[h0b0]

very oddly, I just retested and got this...



I checked my router and it is reporting these speeds over the last few days. I can not find a reason for the speeds coming up to expectation but not complaining.