Thanks for all the feedback.
The house and garage are twelve years old and everything was installed by the builders except for the Junction Box in the garage which powers the security light (I connected into the lighting circuit some years ago to do that). I also extended the power lead that feeds out of the Fused Connection Box in the garage by connecting into the back of the double socket that the builders installed ( not pictured). Consequently, my knowledge of exactly what is there is a bit limited.
Inside the house no cables are visible and I can only tell that the RCCB feeds the garage by switching it to OFF and watching the garage lights go out. The Consumer Unit which sits above the RCCB only supplies the house so there is no mcb feeding the RCCB. The small grey box adjacent to the RCCB has the name Frieldland on it, and is part of the front door bell system.
Inside the metal box, the seven white wires are serially numbered 1 to 7 but there are no other markings at all. There is no marking on the armoured cable.
The cable running from the metal box to the fused connection unit was clearly dragged along the ground at some time because the markings have all but disappeared. However, that it not too important as I can easily replace it, as I can the rest of the system inside the garage.
A ring has some advantages in that the metal box is at the rear of the garage in a corner and I want to install sockets near to the front, along the rear wall, on the opposite side wall and up in the roof (to feed a door opener). A ring seems to be the obvious solution, but I wasn't sure if this was permissible when it was supplied by a single "cable" (i.e. the white wires). The shed would then be spurred off that ring.
The four white wires operating the two way light, which seem to be the same size as the three delivering power, have changed colour to the more conventional red, black, yellow, earth by the time they appear in the light switch in the house. There is no obvious junction box inside the house where they connect into the ring. I know that they do draw power from one of the rings in the house because the light goes out when I switch the mcb in the Consumer Unit OFF.
It seems to me that the fundamental question is the size of the three underground power (live, neutral earth) cables. Can it be measured ?
One further question, I have acquired an old laboratory bench to use in the garage and there is provision for sockets to be mounted on an upstand on the bench. When assembled, the bench will be immovable. Am I correct in assuming that I will need Fused Connection Boxes on the ring to feed each socket which will be several inches away from rear wall of the garage to which the ring will be fixed. ?
Thanks again for the help.
And needs some TLC.
