Structured Wiring & LAU's

[Osprey]

Completed my CAT 5 terminations (T568B) and my Clarity modified Microfilters & NTE5's have arrived.

Intend following advice given here (Peter Parry amongst others) to patch across only 2 & 5 from the filtered side of the NTE5 to the CAT5 patch panels, and then use PABX master LAU at each faceplate outlet where I want phones.

This is to avoid any issue with the Microfilter not providing enough REN - each LAU having it's own capacitor.

To achieve this I have a number of CAT 5 ways on one of the patch panels 'paralled' so as long as I plug my filtered POTS feed into one 'way' I can patch out from the other 'paralled' ways to any of the outgoing 'ways' on normal panels to room outlets.

I could play about until it works, but does anybody know what connections on a RJ45 plug I need to connect the POTS ?

The LAU's show that it has phone across 2 and 5 of the BT socket (normal) and these connect to pins 5 & 4 respectively on the RJ45 plug. The capacitor is connected across pins 5 & 4 of the BT socket.

This is the bit where it is slightly confusing as the capacitor is normally across 2 & 3 ?

So does that mean standard phones with BT 431 plugs pre-wired will not work ? as they will expect ringing on 3 and it will be on 4

[Dave Plowman (News)]

I've got one filter where the line comes in. Goes to my router and normal telephone wiring. I've got 8 phones and they all ring. They consist of four ordinary phones and 3 cordless base stations.

[Lurch]

On 23 Feb 2007 16:02:44 -0800, "Osprey" mused:

Not quite, REN is the amount of line current available to drive the ringer circuit. Doesn't matter how you wire your phones, the REN is the same.

Think of REN as like your main fuse by the electric meter and the phones like electrical appliances.

Pins 4 & 5 (blue pair on 568B wiring). Why do you need to connect any RJ45 plugs up though, just use a standard patch cable between the voice port and data port on the patch panel and plug the LAU into the data outlet.

I'd imagine the 'capacitor' is in fact a surge arrestor as these are the only things normally fitted across 2 & 5.

Just plug one in, it'll work or it won't.

[Osprey]

No 100% certain it's the ringing capacitor.

You may have misunderstood - I'll try again.

The advice I had (from many here & on Automated home) was to parallel a number of ways on the back of a patch panel .... then by feeding a single POTS feed into the front of this 'paralleled' set ... a patch lead from any other socket on this set will distribute the POTS to the outgoing patch panel sockets.

perhaps this drawing will explain:

allows me to patch in or out phones to the 'paralleled ways' as I want.

Which may be what you describe as " just use a standard patch cable between the voice port and data port on the patch panel and plug the LAU into the data outlet."

The advice given by several people was that while REN is limited by the AC current sent by the ringing generator in the BT exchange - it is affected by being fed by via one ringing capacitor if a single microfilter is being used.

As I have RJ45 outlets in each room, an LAU is used, again the advice here was to use PBX Master LAU.

These most definitely have phone across 2 & 5 and there is a standard ringing capacitor across 4 &5 .. Here is the manufacturers data sheet -

patch across 2 & 5 from NTE5, (to 4 & 5 on patch panels you suggest) .. I am still unsure of the capacitor connection at LAU ... it is across 4 &5 on the BT socket side ... and not sure how that is going to work where a phone expects ringing across 3 & 5.

[Lurch]

On 24 Feb 2007 03:23:38 -0800, "Osprey" mused:

Yeah, that's pretty much what I was getting at. I've got the same setup at home, but rather thean pach the phone feed into the front it's punched down on the back so the patch panel sockets are purely outlets for distribution to data sockets.

Yes, think I see what you're getting at here.

It'll be fine, just plug it all in! If it's wrong, it won't work, if it works then it saves me explaining why it will .

I think you may have counted something upside down somewhere which could be causing confusion, like for instance on a BT431a pin1 goes to pin6 in a BT socket.

Anyway, just plug it all in. ;)

[John Rumm]

Ah, well sort of - you have been caught out by a none to smart bit of engineering.

As you rightly say the ring signal is presented to pin 3 on the plug of your telephone. However in order to make connection to this wire on the BT socket, you need to connect it to the pin labelled 4 on the socket. This is because some bright spark numbered the pins in opposite directions on plugs and sockets. So the correct assignments are pin1 on socket goes to pin 6 on plug, 2->5 3->4 4->3 5->2 6->1

Should all work out nicely in the end!

[Roger Mills]

Be aware that there seem to be two alternative numbering systems in use for the pins in BT modular plugs - counting from opposite ends!

The ringer capacitor in a BT master socket is connected between 2 and 3 in one system. In the other system, this would equate to 5 and 4 - which is what you appear to have with your LAUs. Chances are that they will work ok.

[Andy Wade]

No, there's only one system, but it's true that the pin numbering of the modular connector runs the opposite way to the terminal numbering of the line jack units (LJUs). LJU terminal 1 goes to connector pin 6 and so on. Connector pin 6 is the one nearest the springy latch/release lever. People normally refer to the LJU terminal numbers unless talking about the D-shaped cordage on the phone (CPE) side.

A master LJU has a 1.8 uF cap between terminals 2 & 3 (corresponding to pins 4& 5 on the connector side). Terminal 2 should be the B-wire of the line (at about -50 V to earth when all phones are on-hook).

That sounds right then. Micro filters and LAUs tend to have a smaller value capacitor, which is why they can only support a higher impedance ringer load (lower REN number).

[John Rumm]

Is this to save space, or to allow for the fact that there will often be several microfilters connected in parallel?

[Dave Liquorice]

The single C in the master socket is how the POTS system should be configured with the ringing line distributed to all extension sockets.

I'd be a litle concerned about all the additional C's in the LAUs affecting the response of microfilter in some way and messing up your ADSL. Remember that the POTS side is the filtered side not the ADSL which is straight through.

There are also some reports that connecting the unbalanced ring line back into the NTE filter is not a good idea as it injects noise and thus reduces the ADSL performance. So there maybe a case for only bring 2 & 5 from the NTE to your patch panel but deriving the ring signal there with a single, (proper sized) C for distribution.

[Andy Wade]

It will save space and cost, but I suspect the designer's viewpo "Note that the standard BT PSTN CPE interface is a 3 wire circuit whereby the bell wire is AC-coupled from line B. This bell wire must either be filtered by the filter or left open circuit at the Line Port and recreated at the Telephony Port of the filter. This is may be achieved using a 1.8 µF capacitor between line B (pin 5) and the bell wire (pin 4) at the Telephony Port."

[Osprey]

I read some posts on that - but it added that using a PBX master LAu and therefore a local capaictor for each phone was the solution - hence the way I am going.

I suppose if I have problems all I would have to do is add a single link at the patch panel for ringing back to 3 at the NTE5, and swap LAU master for LAU secondary.

[Osprey]

You right I had forgotten that BT went their own way on numberring - and annoyingly I did know this.

I'll find out today if it works !

[Osprey]

and recreated at the Telephony Port of the filter. This is may be

ahhh ... meets my needs then ? glad BT thought of me :-)

I'll only have 2 & 5 connected across to Patch Panel - as mentioned that can help prevent Broadband degradation due to unbalanced ring back - also avoid third wire acting as aerial when no phone off hook.

[Osprey]

ed using a 1.8 =B5F capacitor between line B (pin 5) and the bell

As mentioned in one of the replies, I think the Tech sheet of the manufacturer was mixing up BT socket & plug numbering ... I finished my CAT 5 termination today and all works perfectly.

For ease of use I have created 2 new 'NTE5 masters' in Node zero ... used a pre-installed piece of CAT5 to do this from the BT demarc point. Did this so in the event of any line issues I can simply pull off lower half front plates of NTE5 to isolate house from lines. To avoid any test issues I removed the Out-of-Service resistors from these 'new' NTE5's ... I just connected A+B legs between the BT NTE5's and my own.

I then connected A+B on my phone only line to Patch panels (2 & 5 on NTE5 to B & A resp) made sure I had -48V on B.

The PBX master LAU then generates the local ringing via in-built capacitor. (as it should)

On the 2nd line - I used a Clarity microfilter faceplate, I again distributed only filtered POTS (2 & 5) to the voice patch panel, and A&B to my DSL router.

Glad to say all working fine.

I was pretty pleased out of 32 terminated sockets only one did not test properly with LAN tester ... that had a bad connection on one pin on the outlet.