Baffling phone socket wiring

[Mark Carver]

A friend of mine asked for my help with his daughter's house she's just moved into.

The issue was that she had a telephone socket on a cable hanging in mid-air in a door way. The cable vanished into the door frame at the top. They wanted to know whether it could be chopped off, as she had her broadband working using another socket found in the living room.

Anyway, I went round.

1970s mid terrace house.  First thing, I could find no evidence where the BT cable entered from outside.

The working socket was a dual socket, non branded, unable to be removed because a radiator pipe passed horizontally across the top of it. In any case the fixing screws appeared to have been sealed up with No More Nails.

The other side of the wall was a little white BT branded junction box. I took the lid off, and inside was a single bit of 4 pair cable, and using 'Jellybeans' the Orange/White, Blue/White, and Green White cores had been paralleled together, as had the White/Or, White/Blue, White/Green.

The 'Brown' pair wasn't connected at all.

Finally the offending hanging socket was a BT branded master socket. I plugged a phone in and it worked. I checked for continuity with the brown pair on the mystery junction box. Nothing.

In the end, because that appeared to be the actual real master socket, I shortened the cable, and re-attached the socket to the wall at the top of the door frame. Impossible to determine WTF was going on. The use of Jellybeans, indicates BT involvement, generally not used by DIY bodgers ?

Another wacky discovery was a BT ISDN terminal on the wall in the spare bedroom, feeding two sockets. Again impossible to see where the cable from the outside world was coming in.

[williamwright]

No good turn goes unpunished.

Bill

[Mike Humphrey]

That is odd - but I think it's likely that one pair goes to each of the sockets on the double socket, and the third pair somehow leads back to the master socket. I can't see why it would be done like that rather than making the connections in the socket backbox though.

Is this an NTE5? The type that has a split in the middle? If so, you should find one of the pairs from your junction box connected to the front half. If not, there's another junction box somewhere.

Jelly crimps would tend to suggest professional involvement, yes - though of course an initially sensible installation could have been altered later. And anyone can buy jelly crimps on eBay if they want...

This is starting to sound like there's a good bit of redundant wiring about. ISDN in a home is quite unusual - presumably someone had a home office in the spare bedroom. Most likely both of these will go back to the same point where you'll find the missing junction box.

Mike

[Mark Carver]

No. It was a little 68mm square thing, like this:-

Only Pins 2,3 and 5 were connected (using the correct colour codes)

Just to add to (their) confusion was a legacy ntl branded NTE-5 :-)  That was traceable back to the outside.

Also, the package they have doesn't have any phone line, either VoIP or POTs. The line still had 50v across it. No dial tone, just silence, though if I randomly bashed the 'hook' on and off, I could provoke an NU tone.

So it wasn't possible to see whether the ring circuit was working at all sockets, as part of the diagnosis.

[Dave Plowman (News]

BT connections for single line domestic

Here are the standard colours of cable, flex and their terminals.

Old Terminal New Cable Cord Function 1 Green/white Orange Spare Blue 2 Blue/white Red B wire (Line) -50v Brown 3 Orange/white Blue Shunt wire. (Bell) Green 4 White/orange Green Local earth (Not usually used) Orange 5 White/blue White A wire (Line) 0v 6 White/green Black Spare

[Mark Carver]

Yes indeed. Only really 1.5 pairs are used. I was more interested in using the brown pair to work out if at any point I was at both ends of the same cable. It seems I wasn't.

And the craziness of effectively paralleling 1,2,3 together, and 4,5,6 together on the end of the 4 pair cable. As Mike said, most likely they were going to the un-removable double socket the other side of the wall. Both sockets on it were active BTW.

[SH]

There used to be a product called Home Highway that was based on ISDN aimed at people who wanted more speed than a 56k dial up could provide.

ISTR Home Highway offering 128 kb/s....

[Roger Hayter]

If there was a Home Highway ISDN connection at some point the BT supplied terminal equipment had connections for two different PSTN-emulating connections and two analogue numbers were part of the package. So the two sockets could be using two different pairs to connect to two separate circuits. There could then be two different ring wires, utilising three pairs in all.