Extending a branch circuit in a room to add an extra socket is a better choice than using electric extension cords. The simplest method is tapping into an existing receptacle and incorporating wire to bring power to some other site. In the loft space, sheathed cable is fed through the wall into the existing receptacle and again to the new receptacle locations. The cable taps to the power already at the existing receptacle and feeds into the new receptacle.
In the loft space, drill into the wall cavity with a 3/4-inch spade bit over the existing socket you are tapping . Drill another hole to the wall cavity over the new socket place. Use a jab saw to cut out the outline of the remodel socket box in the new site.
Turn off power to the circuit you are working on and verify it’s off with a no-contact voltage expert at the existing outlet. Remove the socket cover and socket in the electrical box with a screwdriver, but do not get rid of any wires. Feed sheathed cable down the wall and to the socket box you are tapping , and into the new socket box location.
Hold the sheathed cable to the new remodel box cable openings before putting the box to the wall. Place the remodel box in the wall and then turn the screws that extend the wings of the remodel box to hold it in position. Strip 8 inches of cable sheathing from every end of the cable, and 3/4 inch of insulation from the end of every wire. Twist the stripped ends of these cables to a U shape with a very long nose pliers.
Eliminate the bare ground wire from the existing socket and twist it with the bare ground wire in the new cable. Leave a tail on the twisted wires to form to a U shape, join it to the green ground terminal on the socket and tighten it firmly. Place the white wire on the silver terminal therefore that the U shape follows a clockwise route. Attach the black wire to the brass terminal. Tighten the terminal screws firmly.
Connect the ground wire to the brand new socket green ground terminal. Connect the white wire to the silver terminal, together with the U shape following a clockwise route, and the black wire to the brass terminal the same manner. Tighten all terminals firmly with a screwdriver.
Twist the wires behind the sockets and push them into their electrical boxes. Fasten them into the boxes together with the screws and set the covers on the sockets. Turn the power back on at the circuit breaker.
Test the new outlet with a neon voltage expert. Place one lead into the wide slot and another in the narrow slot; the lamp should light. Remove the guide from the wide slot and set it into the round, ground slot; the lamp should light. Remove the guide in the narrow slot and set it to the wide slot; the lamp should not light.