Quick Extension Cabling Question

Evening,

Real quick question about extension cabling. I'm doing some work for my parents and need to install an extension socket (no big deal). I have a spool of CW1724 cable which I understand is basically 2 pair CAT5e cable..

The extension run is about 45ft and the router (VDSL 80/20Mbps) will be plugged into the extension.

Question: Is there any benefit to using the orange pair in the CW1724 cable (which has tighter twists) over the blue pair to connect the extension to the master socket?

Thanks,

Are you wanting to install an extension phone socket for BT 431A plug or an extension RJ45 socket?

Why not experiement ... Try it with the Orange pair, record line stats, attenuation, SNR &c up and down, then try with the Blue pair.

My gues would be there will e some minor differences, but which will be better - no idea.


And yes, CW1724 is Cat5e - you can get 2 & 4 pair versions.

I doubt there would be any noticeable difference. The reason behind the different number of twists between pairs is to reduce crosstalk but if you're only using one pair then there wouldn't be any. But I'd be interested to see the stats for both.

In case you weren’t aware …

fitting an extension from the extension terminals within the NTE will create an issue known as a bridge tap, this will cause varying degrees of FEC errors, and will usually cause DLM to intervene … intermittent sync loss and speed caps.

If the router is at the far end of the extension as the OP has stated it would not be a bridge tap, just a slightly longer incoming line.

@aquilla You need to use the unfiltered extension terminals if have the NTE5C master socket.
A filtered phone extension will not have any Broadband signal on it.

I wouldn't be putting labour into installing phone cable at this point, run an actual Cat5e or Cat6 cable and just use one pair for now, then in the future you can change the ends if you need data.

CW1724 is Cat5e

Not very helpful when it only has two pairs in

Cat5e can have 2 pairs, 4 pairs or lots more.

It was a reply to the OP stating they were considering spending time and effort installing a two pair cable.

But what the OP says is

The extension run is about 45ft and the router (VDSL 80/20Mbps) will be plugged into the extension.

No mention of an SSFP.

If this is a ‘normal’ extension (ie just across 5 and 2 of the standard faceplate) then no matter where the router was connected, either end, that would be a bridge tap.

My understanding of a bridge tap is an *unterminated* pair branched off the main line. This acts as a transmission line to the high frequencies involved in VDSL. The energy goes up the branch and is reflected back at the open end. (It has to go somewhere...) The waves coming back interfere with the waves going up and either cancel each other out or reinforce each other and/or shift phase depending on the frequency and the length of the cable. This interferes with discrete frequencies in the VDSL signal. If the branch is terminated by a modem, this has the right impedance to encourage the energy to continue into the modem in the proper way.

The unterminated branch can also act as an antenna and pick up radio interference.

A suitable terminating resistance, e.g. 600 ohms, could alternatively be used to absorb the energy.

There is another context for 'bridge tap' and this is where a single pair in the distribution network is branched and laid to multiple distribution points for possible future use. I don't know if this was done in UK, but it was in US, where the term may have originated.

There is another context for 'bridge tap' and this is where a single pair in the distribution network is branched and laid to multiple distribution points for possible future use. I don't know if this was done in UK, but it was in US, where the term may have originated.

Correct, and no, doesn’t happen as a rule here.

Don’t agree with the unterminated pair bit.

I disagree, if the router is at the far end of the extension where is the bridge tap?

I would concur with @thinker27 who describes my understanding of a bridge tap.

Your interpretation seems to be different, please explain why you have a different take on the situation.

A TDR would probably see the terminated socket with nothing plugged in, which means it's affecting the signal. It's by no means as much of an issue as star wiring but it depends what sort of SnR headroom you already have on your service.

What do you mean by an terminated socket with noting plugged in? I think the far end of the extension will have a modem/router and possibly a telephone connected.

My understanding is that the incoming line is going into the Openreach NTE and then an unfiltered extension is being installed for the modem to connect to. This NTE will likely show up on a TDR if you went looking for it but I can't see it being a significant event on a trace unless your line is truly marginal.

If you don't also want a phone at the master socket location and you're on an underground feed I'd be tempted to run a new cable through to where the existing underground cable is gel crimped onto the cable that runs indoors and relocate the master. Technically not something you should DIY but it doesn't really matter if you don't screw it up.

This NTE will likely show up on a TDR if you went looking for it but I can't see it being a significant event on a trace unless your line is truly marginal.

If testing at the extension will show a steady stream of of FEC errors… add the bell wire, more still. All these things make for a slightly less happy socket.

Your interpretation seems to be different, please explain why you have a different take on the situation.

20+ years hands on experience faulting these circuits in a myriad different scenarios.

That's not an acceptable answer, just I know best, with no explanation or evidence.

Evening All,

Apologies for the delay in replying. Just been catching up on the comments and thought it would be a simple question.

Thank you for all the comments. I think I will try both pairs (if I have time) and see if there is any difference. I don't expect there to be much difference but I thought someone may have tried this previously.

Just to clarify, there is currently a master (not SSFP) and I will just run an extension which will be a simple BT extension (with BT 431A socket) which is where the router will plug into - nothing fancy (also have a deadline so not much time to go back and forth testing different setups).

Thanks again.

/thread closed..

From the OP’s last post ….

Just to clarify, there is currently a master (not SSFP) and I will just run an extension which will be a simple BT extension (with BT 431A socket) which is where the router will plug into

That set up will produce a bridge tap. There will be errors, and the occasional drop out.