In message , Mike
Humphrey writes
Steven Campbell wrote:

Is it correct that the BT drop wire only has 2 wires connected in the
junction box?
Yet the output side of the junction box that goes to the actual telephone
sockets has 4 wires. So in effect 2 of these wires weren't doing something
or were they?


The external line has only two wires. The master socket splits off a
third, and in some cases a fourth, so the internal line has (up to) four
wires - not all of which are necessarily needed.

The pair that connect direct to the external line are usually blue and
white-blue. These carry voice, ringing, and ADSL. An ADSL router
connects direct to this pair (if you use a filter, the ADSL port is a
pass-through). Phones connect to this pair via a filter, or direct if
ADSL is not in use.

The orange wire is the bell wire, which carries only ringing. Most
phones don't need this and get their ring signal from the blue pair -
unless you have phones with actual bells in. Leaving this unconnected
can improve ADSL - the blue wires are a twisted pair but adding an extra
untwisted wire introduces noise.

The white-orange wire is earth. Nothing uses this nowadays on a standard
phone line, so this is not connected.

The green wires, if present, are not used.

There's something rather odd about your photo. The black cable is
presumably the incoming BT cable. Two pairs are connected, so presumably
two lines. One is crimped to the blue wires leading off the bottom of
the photo, so presumably that leads to a BT master socket. The other
pair goes into the junction box, where it all gets a bit confused. This
is BT's side of the master socket, so there should only be one cable -
but there are two, and the top one looks like cat5 rather than phone
cable (it is marked 4pr, phone cable has only three pairs). Also the
bottom terminal has three wires attached.
There should only be one cable on the right-hand side. The blue wire
should be attached to the top terminal, the white-blue to the bottom
terminal, and nothing to the middle one. The orange and green wires
should not be connected to anything. This should run to a BT master
socket. Any extensions should run from there - either from the removable
front if it's a linebox, or via a plug if it isn't.
It looks like someone has run an extension on the cheap by tapping into
the junction box. If BT find out this has been done then they can refuse
to fix any faults until they've corrected it - which they charge quite a
lot for. Also as the line isn't on a proper pair, it won't do ADSL speed
any good.

Have a look at:
http://www.wppltd.demon.co.uk/WPP/Wiring/UK_telephone/uk_telephone.html

--
ian