Power may be supplied to a spur via a maintenance free junction box inserted in the ring main, provided the limitations of the regulations are not exceeded. An older style screw terminal junction box may also be used provided that it is accessible for inspection, testing and maintenance, and is also securely fixed in position.
You must make quite sure that this circuit is indeed a ring main. If you are not absolutely certain, consult a professional electrician.
1. Plan for the new socket outlet. There will need to be sufficient slack in the existing cables to connect to the junction box. Make sure you check this before starting any work. If there is insufficient slack, new cables will need to be fitted or you may consider Extending the Ring Main to provide power to the new socket.
2. Switch off the power at the consumer unit for the circuit concerned. If you have removable fuses at your consumer unit, switch off the power at the consumer unit and remove the fuse for this circuit.
Adding the new cable
4. Determine the nearest point at which the existing ring main passes the location of the new socket. Run a length of appropriate cable from here into the new socket box ensuring that you allow enough cable for making the connections there and at the junction box.
5. With the new cable fed into the new socket box, strip the cable end ready for connection. See our Cable Stripping Guide for detailed information on this.
6. Cut through the outer sheath of the cable carefully using a pair of side cutters. Be sure not to cut into the insulation of the conductors.
7. Peel back the sheath to reveal the conductors and grip the end of the bare earth conductor with a pair of pliers. Draw the wire back through the sheath like a cheese wire.
8. Cut off the excess sheath with a pair of side cutters.
9. Separate the conductors and trim the insulation of each back by about 1/2" with wire strippers.
10. Insulate the earth conductor using the separately sold green and yellow sleeving. This should be cut to length and fed over the conductor so that about 1/2" is left exposed at the end to match the other conductors.
Connecting the cable to the new socket outlet
11. Slacken the screw of the appropriate connection terminal. Insert the brown (old cable colour = red), live conductor into the hole in the terminal marked ‘L’.
12. Ensure that the conductor is fully housed and that there is no exposed wire showing. Fasten the screw and make sure the wire is firmly secured.
13. Repeat the process for the blue (old cable colour = black), neutral conductor, fixing it into the terminal marked ‘N’.
14. Repeat the process for the green/yellow sleeved earth conductor fixing it into the terminal marked with the earth symbol.
Metal Boxes Only
15. If you have a metal box like the one shown here, an earth tail may be required. One must be fitted between a socket outlet and metal back box where both socket fixing lugs are adjustable. If this is what you have, cut a suitable length of the earth conductor from some cable of the same size as that used for the circuit. Sleeve this with green and yellow sleeving allowing ½” conductor to be exposed at either end.
16. Connect one end of this earth tail to the earth terminal provided at the back of the metal mounting box.
17. Connect the other end of this earth tail with the earth conductor secured to the terminal marked with the earth symbol on the socket outlet.
Fixing the socket outlet
18. Double check that all your connections are to the correct terminals, and securely fastened.
19. Carefully push the face plate back, gently folding the cables as you go, so that they sit neatly into the box.
20. Fasten the face plate with its retaining screws. Tighten the screws alternately to draw the plate back evenly.
21. As you tighten these, ensure that the face is level. One or both of the screw mountings will have allowance for a small amount of vertical adjustment which assists with this.
Connecting to the Ring Main
22. As mentioned earlier, the connection of the spur to the ring may be made with a maintenance free junction box or, a standard junction box provided this is fixed and accessible for maintenance, testing and inspection.
Maintenance Free Junction Box
23. At the point in the ring main where the junction box is to be connected, cut the ring main cable, and strip and prepare the ends.
24. Strip and prepare the end of the new spur cable at this point as well so that you now have three cables ready to be connected to the junction box.
25. Use a maintenance free junction box with push type or cage clamp type terminal blocks of a suitable size and ampage. The box shown here is a Wagobox which is very quick and easy to use.
26. In the pictures you will see 3 pole cage clamp terminals being used. With these, the clamp for each terminal is lifted and the conductor fully inserted so that there is no exposed wire. The clamp is then snapped back down and the conductor securely held.
27. Insert and secure each of the live, brown (old cable colour = red) conductors of the ring main and the live, brown (old cable colour = red) conductor of the new spur into one of the terminal connections and secure.
28. Repeat the process for the neutral, blue (old cable colour = black) conductors of the ring main and, the neutral, blue (old cable colour = black) conductor of the new spur.
29. Repeat the process for the sleeved earth (green/yellow) conductors of the ring main and, the sleeved earth (green/yellow) conductor of the new spur.
30. Double check that the connections are correct – only conductors of matching colour share terminals – and that the insulation of each conductor butts right up to the terminal.
31. Insert the three terminal connectors into the maintenance free junction box. In the pictures you can see how these are held in a slot at the end of the box. Secure the three cables in the cable clamps at the outlets of the maintenance free junction box. This should be clamping a sheathed section of cable so that there is no unsheathed cable outside the box.
32. Secure the junction box. On some models, there is a fixing bracket that can be positioned first and the box then simply attached.
33. Clip cables securely.
Standard junction box
34. Alternatively, provided that the junction box will remain accessible for testing, maintenance and inspection, a standard junction box may be used. Mount the 30 amp junction box by screwing to a suitable surface. You may need to fit a wooden batten to support it on.
35. Depending on the type of junction box, you may need to tap out three of the blanked side access points. Other types allow the cover to be rotated to provide the required number of access points.
36. With the cover of the junction box removed, lay the ring main cable alongside. Cut the cable at the middle of the box.
37. Strip and prepare the ends of the cut ring main cable ensuring that each conductor is long enough to reach its terminal. Note too that where the outer sheath has been removed from the cable, this section must stay within the junction box.
38. Strip and prepare the end of the new spur cable in a similar fashion.
39. Slacken the terminal screws in the junction box. Fit the exposed section of the live, brown (old cable colour = red) conductor in one of the outer terminals and fit the live, brown (old cable colour = red) conductor of the new spur with it.
40. Tighten the screw to secure these conductors.
41. Place the three earth (green/yellow) conductors in one of the other terminals and secure with the terminal screw.
42. Repeat the process for the neutral, blue (old cable colour = black) conductors using one of the other terminals.
43. Double check that the connections are correct – only conductors of matching colour share terminals – and that the insulation of each conductor butts right up to the terminal.
44. Ensuring that the unsheathed sections of cable are well within the box, replace the junction box cover, rotating if necessary to suit the entry points and fasten its retaining screw.
45. Clip cables securely.
Completion of work
46. Once you are sure that all work has been completed correctly, switch the power back on at the consumer unit. In the case of removable fuses, replace the fuse for the circuit, and switch the power back on.
47. Check your new socket to ensure that it is working properly.