Quick question about Cat 5

No3ntry · 3 Sep 2011 at 03:05

I bought 100m of very cheap Cat 5e off a famous auction site and when it turned up it wasnt twisted pair (in fact the outer sheathing was very loose) I wired one wire up to a network port and tested with a cheap network cable tester and it tested ok (no computers on site at present to test network speed)

My question is what difference does the twisted pair make as far as a 10/100 network is concerned, cable lengths will be absolute max 6m (most likely less than this)

My first thought was that I am reluctant to use it but it seems a shame to throw it if it can actually be used.

Thanks
James

bremen1874 · 3 Sep 2011 at 03:13

Cat5e has a fairly loose outer sheath.

Inside the sheath there are 4 pairs of wires.

Each pair of wires is twisted together. If the pairs aren't twisted then it definately isn't Cat5e.

If it really isn't twisted pair then it's not worth bothering with and needs to go back or into the bin.

No3ntry · 3 Sep 2011 at 03:36

it was advertised as cat 5e, it defo isn't twisted pair.
The colours aren't in spec either.
1 dark blue
1 light blue
1 dark green
1 light green
1 red
1 white
1 dark grey
1 light grey

dunno what it is, I paid £14 inc delivery I dont think it is worth the hassles of trying to send it back tbh.

Have just ordered some more now, made sure it is UTP this time though.

Thanks
James

bremen1874 · 3 Sep 2011 at 03:50

It all sounds very odd. Is the suspect cable labelled down its length?

Tealc · 3 Sep 2011 at 09:11

The cable will need to be twisted pair for it to have any form of interference suppression. It sounds like you've been supplied with a generic 8 core unshielded cable.

Each of the four pairs in a Cat 5 cable has differing precise number of twists per metre based on prime numbers to minimize crosstalk between the pairs. On average there are 6 twists per 5 centimetres

Electrically the cable will work if you substitute colours for Cat5e colouring and wire both ends up with respect to that. Signals though won't be so good though and I certainly wouldn't use the full 100m but I'd have thought it would be just about ok for small runs of a few metres at 100mbps.

No3ntry · 3 Sep 2011 at 13:38

On further inspection today, 2 pairs are twisted, the other 4 wires are not.

I think for the sake of £14 it isnt worth taking the risk of running into problems down the line, even though I agree with you Tealc that i would probably be alright using the short runs that I intend to.

Thanks
James

Dist · 3 Sep 2011 at 14:40

If you only care about 10/100 Mb/s then 2 pairs is all you need, you only need all 4 pairs if you want 1000 Mb/s, so you could just use the 2 pairs that are twisted.

That being said though, even if there are 2 pairs twisted it would be hard to tell if they are consistently twisted and twisted the correct number of times for x distance.