In my case the new cable goes round the outside of the house. Perhaps there's two cables one up, one down but that sounds unlikely knowing BT. I'll check when I get home 
Lol. Sorta. Gotta love the phone wiring for this house. Three cables come out from behind the entry cover and go around a corner and up the wall. Two of them go into a hole half way up - they are feeding what I can only describe as a 'double master' socket in the second bedroom. It's a twin socket with a horizontal cut along the middle. Curiously it's marked up with what seems to be a range of numbers:
705324 - 705327 (no, not my current number <g>). Can two sockets really provide four numbers?
Anyway the third cable runs along the roof line, around another corner and down to feed the only active master in my study. Presumably one pair goes up to the new master, and the second pair connects back to the original master. So it's dodgy wiring as suggested :-/
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Andrue Cope
Brackley, UK
Edited by Andrue (Thu 01-May-14 20:20:23)