I have a BT line which terminates at a BT master socket. I also have a Cat 5e patch panel, which is connected to various RJ45 sockets around the property.
I want to convert five of the RJ45 sockets to phone points so I bought some PSTN line adapters from Comlynx:
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the patch panel, I intend to wire five spare ports in parallel back to terminals 2 and 5 in the BT master socket. I can then patch across to the port that has a phone on it.
My question is this: The Comlynx adaptors have a capacitor/resistor/surge suppressor in them. If I use five of them in parallel, won't it mess up the ring tone?
I know that this is the reason that you can't wire BT master sockets in parallel. The same would apply to the adapters I would have thought.
Probably not... the capacitor is only shunting the ring line from one of the exchange lines. Extra capacitance will just *lower* the minimum switching frequency that can "get through" the cap. Since I doubt you will be using pulse dial phones, or ones with real bells for ringers, it should not make any difference.
If you want a more flexible solution, you can pick up a cheap analogue PABX from the far east via ebay. Then it certainly becomes a non issue. (I have a 4/16 line/ext PABX waiting to go it when the required round tuit is acquired and the structured wiring is done)
It depends on the value of those parts. The short story is you've got the wrong items, you just want plug to socket adaptors, not stuff with circuitry in it. Another option is to have a phone socket on the wall next to the rj45 skt.
All you need do is connect the right sockets all in parallel, you dont need a single electronic component anywhere.
Not really - you could replace the cap with a wire and the phones would still work[1]. The more caps you have the more the connection between the exchange wire and the ring wire looks like a "wire"
[1] Many countries use two wire phone systems anyway. The only reason for the inclusion of the ring wire was to prevent the bell on the phone from "tinkling" when pulse dialing on another extension.
Yup, agreed. An ordinary secondary LAU is what is required.
Kind of defeats the point of structured cabling though ;-)
agreed, unless you want to do extra stuff like being able to route calls between rooms etc, or share multiple exchange lines effectively.
It shouldn't as the capacitor will be on the output side of the socket. it bridges to pin 3 on the BT side, and pin 3 won't be present on the cat-5 side.
Looking at the data sheet, it suggests that part 42-212 is a straight-through device with no active components. If you're paralleling up 5 sockets, maybe thats the one to use... (And wire to pins 4 & 5 on the cat-5 side)
No, that's fine. You don't need the resistor and probably not the surge suppressor (unless your cat 5 lines are long and/or between buildings), but they do no harm either.
The capacitors will each be feeding an individual phone -- to say they are in parallel is rather misleading, and as they usually only feed one appliance in this situation (and have to fit in a small space), they're usually quite a bit lower value than the one in the master socket that has to get a REN of 4 though it. Also, the one in the master socket is not being used at all, because when you carry phone over structured cabling, you do not carry the bell wire -- it's recreated separately at each socket outlet by those capacitors.
The bit that matters for parallel connecting, the bell wire (pin 3), isn't being connected at all between your adaptors.
As Owain says, I suppose I could buy some "no components" adaptors and connect the bell wire from the master socket pin 3 to the patch panel. This way would be identical electrically to wiring secondary phone sockets to the BT master.
However, since I already have the Comlynx PSTN master adaptors, I'll try first with just connecting master socket pins 2 and 5 only.
Not sure which of the above two options is "industry standard" when using structured wiring.
I will reserve 8 ports on the patch panel for PABX phone extensions.
If I use a PABX, I have three issues to resolve.
What pins on the patch panel do I wire the four-core PABX outout extension cables to? What RJ45 adapter should I use if want to plug a PABX system phone?* What RJ45 adapter should I use if I want to plug in an analogue PSTN phone?**
You never connect pin 3 through structured cabling. There's no way to balance the current in twisted pairs if you did so, making the circuit much more liable to both generate and pickup interference from other circuits in the structured cabling. You'd need twisted triples, which don't exist in structured cabling (or anywhere I can think of).
You only need all the pin 3's connected together if you've got pulse dialing phones, and bells in other phones on the same line which are liable to 'tinkle' when pulse dialing is taking place (and you care about stopping the bell tinkle). Frankly, that never occurs in phone systems installed on top of structured cabling.
That is not true. A LOT of phones wont ring without the third wire connected.
And what you said about CAT5 and balancing, is with respect, bollocks.
The third wire ONLY carries the ring current.
Which is so low frequency as to be irrelevant to almost anything else using the cabling.
The real reason why the standards are the way they are, is because structured phone wiring implies PABX and PABX use a two wire multiple master system. Or a 4 wire digital system.
I.e. by the time you now you want structured wiring, you are long past the time when its one phone, three extensions and no PABX...
We've run Ethernet and phone down tme SAME cat 5 cables in extremis..splitting the pairs so that different stuff runs on different pairs. No interference.
( note that the BT wiring shows pins 1-6 and also in reverse, 6-1.This is due to a spectacular c*ck-up where the plug and socket numbering is reversed from each other! I tend to always use the designation where 3 is the ring, although you will also see it designated as 4. )
So now you know there are 3 different typed of LAUs ( tha adapters you linked to ).
PSTN masters: contains ring cap, resistor, and surge suppressor. PABX masters: contains ring cap. Secondary: contains nothing, only wiring.
PSTN masters are intended to be used where the 2-wire raw incoming line is presented over the structured wiring on pins 4+5. All the functions of a normal BT master are provided in the LAU, including generating the ring signal on pin 3 of the BT connector.
PABX masters are similar: they take a 2-wire signal from a PBX over pins 4+5 of the structured wiring, and generate the ring signal on pin 3. They just ommit the surge arrestor, since the line is not coming in from overhead plant.
Secondaries require you to have a master ( eg NTE5 ) elsewhere, and take a
3-wire feed in over the structured wiring: the line pair on 4+5 destined for pins 2+5 of the BT connector, and the ring signal on 2 destined for BT pin
In my installation, which is pretty much the same as yours, you should really use secondaries. The raw incoming BT line goes to A+B on the BT master, and then you wire from the extension outlets on the master pins 2,5 and 3 up to the patch panel. The mastering is provided by the NTE5, and the ring signal is carried over pin 2 of the Cat6 to the LAUs. The line pair is carried over pins 4+5 of the Cat6 to the LAUs.
In this way, you will have the same config as normal secondary extensions, with no multiple masters to worry about.
No, any current has to be carried by at least two wires, and irrespective of carrying current, it's coupled through the ring capacitor to one of the pair, and acts as an antenna and/or capacitive coupler to other signals (particularly to other similar unbalanced antennae wires).
The fundamental is low, but from PABX's is usually not a sine wave (worse case square wave), so it's stuffed full of harmonics. The interference is clearly audiable if you stuff two 3-wire phone circuits down the same cable bundle, and that stuffed up modems back when they were in common use.
Loads of PABX's (pretty well all at one point) use exactly the BT system, because they use(d) exactly the same kit. You still never carried the bell wire, as that caused very audiable interference on other pairs. (You would only link it locally between extentions on the same line.)
Ethernet, being properly balanced pairs, will neither transmit nor receive from unbalanced antennae wires (and the frequencies are so different it's unlikely there would be any problem even if they did).
Sorry, but that's not my experience. The unbalanced ring wire will pick up all sorts of HF interference and couple it back, via the capacitor onto one of the speech pairs. If this is done anywhere near a pair carrying a DSL signal, then it will be seen as noise for the DSL signal.
If you are wiring just phones, then ring wire HF interference doesn't matter. (But I can hear ring current crosstalk if pin-3 is extended over structured cabling). IMO, if you are running phones over structured wiring, then you are better using PBX mastering modules, or plug-in converters with ring capacitors to generate the ringing signal on pin 3 at the remote end, so you maintin the twisted-pair integrity of your structured wiring.
If you split the Ethernet pairs, then don't expect auto rate detect to work. You'll have to nail everything to 10Mbps. I spent some time on one job rewiring all the Ethernet cables that had been done by an electrician using 1-2, 3-4, 5-6 & 7-8 for the pairs. It worked fine when everything was 10Mbps, then they started introducing 100Mbps...
Using two Ethernets down one cat-5 cable, keeipn the standard two pairs for one circuit and using the spare two pairs= for the other circuit also works fine - until they go to Gigabit...
The extension cables on the PABX will be 2 wire typically on a analogue PABX. Typically you would use a two wire RJ11 to RJ11 lead and plug one end into the PABX RJ11 socket and the other into the RJ45 socket on the patch panel. (RJ11s fit RJ45 sockets - they just can't connect to the two outer pins)
You want a PABX master - i.e. a ring capacitor and nothing else. Most analogue only PABX are controlled via an ordinary touch tone phone rather than a system one.
So what? Its part of a twisted pair..ground that and its effectively 'shielded'. We aren't talking abiout running broadband on it or teh other pairs. Just audio.
The OP specifically is NOT using a a PABX which is why he HAS to carry the third wire.
So this isn't relevant.
is usually not a
HE ISN"T USING A PABX WHICH IS WHY HE NEEDS THE THIRD WIRE.,
Exactly. Etherenet wont be an issue as its almost 100% immine from low level interference.
As far as crosstalk between the phone exte=nsions goes, well had you not realised that:
NO PABX IS INVOLVED
i.e. they are all carrying the SAME speech circuit.
I,e waht I said at the outset, you are talking standard PABX structured able. He is NOT using it that way. If you run two wire from the BT incoming you need 5 master sockets to regenerate the ring wire locally. AN that is against BT rules for their lines: you are only allowed to run one ring generator circuit AFAICR.
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