I mean, the simplest answer is to lay a new cable, and that is definitely what I am going to do - that’s not my question.

But this is a long run, and it would be neat if I could salvage some of that cable. How can I discover where the cable is damaged?

One stupid solution would be to halve the cable and crimp each end, and then test each new cable. Repeat iteratively. I would end up with a few broken cables and a bunch of tested cables, but they might be short.

How do the pro’s do this? (Short of throwing the whole thing away!)

37 points

Higher end cable testers can show you where the break is, but it will be far more expensive that a new cable.

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15 points

My TP link switch can detect faults and cable length. I’m not sure it can do both together but it’s possible. Worth checking if you have a switch with those features

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4 points

Hmm, interesting! I have a Synology switch, gotta read up on its capabilities.

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3 points

you can rent a time domain reflectometer for this purpose… it sends out a signal and then listens for the echos back and calculates the distance. problem is they arent accurate the first like 500 feet so you have to add a reel of 500 ft of matching cable to the end first. electrorent.com rents them.

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1 point

I had an AMD Phenom-II era motherboard that claimed it would be able to do that. OP, you might be able to find an old NIC/mobo that could do this for cheap.

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20 points
5 points

Should also be able to do it with a NanoVNA or similar.

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That sounds triggered.

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12 points
*

You can only do 100M runs max anyways, just replace the whole thing? 100M of CAT6 is pretty cheap if you already have a box for it.

Or is this an academic question?

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7 points

Actual, not academic. And I agree that a new cable is cheap, which is what I will do. My question is about avoiding throwing a mostly good cable in the trash.

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3 points
*

Pull it, cut into quarters. Add jacks to each end and test the lines.

Nvm, I see you suggested this…

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-4 points

What is an M? Miles? That doesn’t seem right.

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0 points

M = meters. Mi = miles

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4 points

m = meters. M = mega (x 1 000 000).

That’s why Km is 1 thousand meters and Mm is 1 million meters.

The actual unit is lower case, the multiplier is uppercase.

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7 points

If you just want some spare cable. I’d make 5x 20M pieces. The one that doesn’t work becomes 2x 10M. That bad one becomes 2x 5M … As far down as you like.

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2 points

Isn’t that almost what they suggested except starting at a different size and doing a binary search basically? You’re just starting the binary search after the first step of cutting into 5 lengths instead of 2.

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3 points

The easiest thing to do would just be to pull it out and look at it. The break might be obvious.

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1 point

Yeah, that’s not that easy, unfortunately, because each end of the network cable passes through an insulated wall, through a hole equal to the cable width = smaller than the plug. Even if I find the break, it is likely in the outdoors part of the cable where I would want an unbroken cable without a field repair.

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2 points

Sure, but you’re going to be pulling it out either way. When you do, inspect it.

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