Extending electrical circuits

The easiest way of adding a new socket outlet or a fused connection unit (FCU) is to run a spur from an existing socket. Using a continuity tester, check that the socket is not itself supplied by a spur or supplying another spur.

• Cut off the power supply to the relevant circuit from the consumer unit.
• Remove the face-plate from the socket you will be running a spur from.
• Knock out the tab in the side of the mounting box to admit a new cable.
• Prepare the cable route from the existing socket outlet to the position of the new socket or FCU. If you do not wish to cut a chase in the walls, you can conceal the cables with trunking.
• Fix the new socket mounting box to the wall, following the directions for installing a mounting box
• Measure the distance between the old and new sockets and cut a length of cable to fit between them.
• Feed the cable into both mounting boxes.
• Prepare the cable ends.
• At the new outlet, connect the live core (brown) to terminal L.
• At the existing socket outlet, connect the new cable cores to the corresponding terminals. If the wiring is colour-coded according to the old system, you may need to connect 1 red and 1 brown core to the live terminal, and 1black and 1 blue core to the neutral terminal.

If you have floorboards, it may be easier to run the spur directly from the ring main circuit cable under the floor via a 30 amp three-terminal junction box.

• Cut off the power supply to the relevant circuit from the consumer unit.
• Lift the floorboards near an existing socket outlet to locate the circuit cable.
• Check that you have the right cable using a continuity tester.
• Hold the junction box against the side of a joist and cut the cable over the junction box.
• Prepare the cable route from the junction box to the new socket outlet.
• Fix the new socket mounting box following the instructions for installing a mounting box.
• Prepare the ends of the spur cable.
• Connect one end of the cable to the socket face-plate following the instructions for installing a socket.
• Connect the other end to the junction box: connect both ends of the existing circuit cable and the new spur cable to the same terminals in the junction box: earth core to the central terminal; live core (brown/red) to the terminal below right; neutral core (blue/black) to the terminal above left.
• Screw the junction box base to the side of a joist.
• Screw the junction box cover over the base.