I did one place where I needed to pull back a cable running to an outlet. Nothing looked wrong at the receptacle; it was just a conventional 7/.029 T&E (Romex-like). The only problem is, when I started tugging on the cables in the attic I found the top end of it was a 7/.052, or some other much larger cable.
In the end, I found a splice about halfway up the wall and directly above the socket, all buried under plaster in a box of the type we normally use for our "cooker" (range) panels.
It looked like somebody had removed the old range switch and outlet, then just chanelled down to fit a socket below and spliced the smaller cable in the old box. They'd then just stuffed a piece of drywall loosely into the box and plastered over it.
