Problem Understanding Phone Wiring

[vince366]

I realise that nobody other than BT can modify the master socket, but the pic below shows how my old-style socket is wired up.

I have just moved into a new house and just want to get an understanding of how the phone sockets are set up.

Does this look like official BT wiring? I think the previous owner may have added wiring to this!

Thanks in advance,
Paul.

 

[electronicsuk]

A rather odd arrangement you have there. I'd say the white cable has nothing to do with BT, it seems to be for an extension that has been added to a master socket that isn't really designed for hardwired extensions. That isn't to say it wont work, but BT wont support it.

Were there ever two lines in the property? The black cables have been jointed using jellies which suggests a proper job, but all 4 cores of the incoming drop wire are used, and it only takes 2 to carry a single line.

 

[OLD]

The centre black cable has a line on gn/bk and another line is wired on or/wh which connect to w.bl/bl.w of out going cable those wires are going somewere else. your line is on 2&5 of the old type master socket and connect to the w.bl/bl.w to go to a extension in the white cable the w.or should be connected to 3 its the bell anti tinkle wire you can see a bit still there.

 

[vince366]

A rather odd arrangement you have there.

Almost as bizarre as the old wallpaper!

I'd say the white cable has nothing to do with BT, it seems to be for an extension that has been added to a master socket that isn't really designed for hardwired extensions. That isn't to say it wont work, but BT wont support it.

This is what I suspected - There is a phone socket in every room of the house, so I imagine the white cable goes off to serve some if not all of these!

Were there ever two lines in the property? The black cables have been jointed using jellies which suggests a proper job, but all 4 cores of the incoming drop wire are used, and it only takes 2 to carry a single line.

Again, this is what was confusing me! We only have one line so I can't understand why all 4 wires from the drop line are connected. The strange thing is that all extension sockets in the house do actually work, so I'm stumped as to where the 2nd black cable actually goes off to!

I haven't found a 2nd master socket anywhere either.

Is this how BT add a 2nd line then - they use the remaining 2 wires?

Could it have been used for an alarm system? I don't know how they use phone lines so I'm meerely speculating.

I only expected to see the green and black wires connected to the master socket.

Do you think that if the "2nd line" connections and white cabling were removed that just leaving the green and black connections would result in a working master socket (not that I plan to do this myself of course).

I realize that this would render all remaining extensions unusable.

Regards,
Paul

 

[Chri5]

Paul, if you did as you say, you're summary is correct.

Two lines from a drop wire and no obvious reason for the 2nd line?

If you live in a flat or semi, it might serve the neighbours!

Otherwise if your house is stand alone / detached it must be legacy from the previous owners.

Reason could have been for work use (do you have office / study area?), for the nanny / lodger, outbuilding.
Most alarms are BT redcare and that is overlaid on a normal line which can be used around the house.
BT Redcare alarm lines can't carry broadband, so you might have had a line for redcare and another for broadband + voice??

Cut it and see

 

[Taylortwocities]

Yes, that would be my guess too . If you remove the white cable the only socket that will work is the one on the photo. I assume that the master socket in the photo actually works??

The Orange & white on the black incoming cable are probably a (now) redundant second line. One way to check is to cut the orange wire and see if your phones still work!

You could check to see if there is 50v DC betwwen orange and white but it may still be connected at the exchange, even if the line has been disabled by BT.

 

[plugwash]

why are you messing with this in the first place? have you been having problems of some sort?

 

[dal5band]

The normal way is incoming line pair goes to pins 2 & 5 in the master socket.
Any ongoing extension (slave) sockets are connected pins 2,3 &5, all in parallel (i.e 2 to 2, 3 to 3 etc). There is a colour scheme used for wires, if you have BT standard 4 wire around the house.

2 Blue with White Bands
3 Orange with White Bands
4 White with Orange Bands (not actually used for anything)
5 White with Blue Bands

I've never understood the need for pin3, the anti-tincle wire. Other countries seem to manage with just the two line wires.

 

[vince366]

My main reason for looking at this is that I like to know exactly how the house I live in is wired up!

I've done this for every house I've ever lived in and draw up plans for electrics/plumbing/gas etc.

It never hurts to know exactly where everything lives and how it works.

 

[barch]

From my rudimentary understandings of the UK telephone system, we use, possibly used, three wires because the third wire is connected the the bell capacitor which makes, made a BT phone ring. If the thrid wire wasnt connected and you had a old BT rented phone on the line, it wouldnt ring. It would work, but not ring. Most if not all phones manufactured these days would not require connection to a master socket to make them ring because the phones sense a voltage drop between the two line wires when a call is being received.

 

[vince366]

Just wanted to say thanks to everyone who helped me - I have some searching to do over the weekend to see where all these wires go!

At least I now understand what I'm looking at

 

[Space cat]

Most if not all phones manufactured these days would not require connection to a master socket to make them ring because the phones sense a voltage drop between the two line wires when a call is being received.

Some early non-rented phones won't ring without the third wire. I know because I've got one. I also know of a cordless phone that gives a single ring when a dial-up modem hangs up.

Are BT charging you for anything you don't think you've got?

 

[Anteaus]

Some early non-rented phones won't ring without the third wire.

True, although I think you find that the majority of phones these days conform to the American two-wire standard. Why the idiosyncratic three-wire system was ever introduced is a mystery. It does have the advantage that you can stop a phone ringing if you want to, but makes the wiring much more awkward.

The third wire goes to the capacitor (yellow) BTW, which only permits AC to go to the bell. But, the phone usually has an internal capacitor anyway, making the one in the master faceplate redundant.

 

[aptsys]

It's also not that unusual to find someone has (accidentally?) fitted more than one master socket so those phones will still ring without the third wire.

 

[plugwash]

btw removing the third wire is highly reccomended if you use ADSL with multiple seperate filters. From the pic it looks like the orange wire was previously connected on the extention wire but was later removed when someone got broadband.