Let’s say that you are doing some remodeling and you need to move an existing single pole light switch. Well, the easiest way to do this is to change the existing switch box into a junction box.
To do this, turn off the power and verify that it is off at the light switch. Remove the light switch and determine which wire is the power supply and which one goes to the light. Install a new 2 conductor cable with a ground to your new light switch location.
The wire size is determined by the circuit breaker size. A 20 amp circuit requires 12 AWG wire and a 15 amp circuit requires 14 AWG wire. Typically, lighting circuits are on a 15 amp breaker in a home which would require 14/2 NM cable with ground (romex).
Install the new switch box and insert your 2 conductor cable with ground. When you strip the sheath off of the cable you are required to leave at least 1/2 inch of the sheath extending into the switch box.
Be sure to support the 2 conductor cable within 12 inches of the box and every 4 1/2 feet thereafter. I recommend the plastic staples over the metal ones. There is less chance of damaging the cable with the plastic romex staples.
When you terminate wires on the switch you need to re-identify the white wire as a hot wire. To do this either use a black permanent marker or some black electrical tape. You need to do this to both ends of the wire. Now connect the bare copper wire (ground) to the green screw on the light switch.
Connect the re-identified hot wire to one of the brass colored screws on the light switch. It doesn’t matter which one. Connect the black wire to the other brass colored screw on the light switch. Install the light switch and cover plate.
Now go to the old switch box and terminate the ground wire with the other ground wires. If the box is metallic, then you are required to connect the ground wire to the box as well.
Connect the black wire from the new 2 conductor cable to the black wire going to the light. Connect the re-identified hot wire in the new 2 conductor cable to the black power supply wire.
Tuck the wires into the box and place a blank cover over the box. Turn on the power and test.