Netonix Forums

I'm wondering how accurate cable diagnostics are.

I'm seeing this result even after putting new ends on a cable.

Pair 1 Status
Ok

Pair 2 Status
Ok

Pair 3 Status
Short

Pair 4 Status
Short


Pair 1 Length
29.53
ft / 9m

Pair 2 Length
29.53
ft / 9m

Pair 3 Length
19.68
ft / 6m

Pair 4 Length
3.28
ft / 1m

Cable diagnostics is pretty accurate but somethings can throw it off like things like Ethernet Surge Protectors, stretch or kinked wires, bad ends, and some devices.

There are many posts I made about this, here is one: viewtopic.php?f=6&t=644&p=4604&hilit=stretched#p4604

Some devices on the other end will cause cable lengths to be reported incorrectly when they are plugged in but not powered up.

As far as seeing this:
OK
OK
SHORT
SHORT

This is normal with any ubnt airMAX 10/100 device as they have pairs 3 and 4 shorted together to carry POE power.

As far as pair lengths being reported different that can be caused by 3 things:
1) Cable was damaged during installation, it was stretched or kinked
2) Some devices when not powered up will cause pair lengths to be reported incorrectly.
3) Ethernet Surge protectors - results vary depending on unit used.

Why not search for all the posts you can find on this issue searching for things like "Cable Diagnostic", "cable test", and such as I have done some LONG WINDED posts on this already.

It's pretty typical for the pair length to be slightly different even in perfect cable.
I ran a Fluke DTX-1800 on many a cable and they almost never come out the same length.
Mostly because that's the wait the cable is designed. If you look closely there is a different amount of twist for the pairs. This makes some longer and some shorter.