Piggybacking is a wiring technique that jumps from one junction box to another. As long as the maximum amount of amperage per circuit is observed, this technique is safe. Piggybacking is possible because of the four wiring terminals found on each outlet and is a standard process when wiring a home. Piggybacking is a convenient method of adding a new outlet or switch.
Things You'll Need
10/32 ground screw
Turn off power to the existing switch or outlet at the main electrical panel.
Remove the two screws securing the cover plate on the existing switch, or the single screw for the outlet, with the standard screwdriver.
Remove the two screws holding the existing outlet and switch into the junction box. Pull the outlet or switch from the box.
Punch one of the unoccupied knockouts on the junction box housing the existing outlet or switch using the hammer and standard screwdriver.
Slide the new ROMEX® wire into the existing box. Strip four inches of outer insulation from the new wire. Strip an additional inch from the black and white inner conductors.
Locate the two unused brass, silver, and green screws on the existing fixture. Loosen these with the Philips screwdriver.
Slide the black wire on the new ROMEX® lead into the brass-colored screw. Slip the white wire under the silver, and the bare wire to a 10/32 green ground screw on the threaded hole on the junction box. Tighten all three to secure these in place.
Push all the wires and the outlet back into the junction box. Screw the outlet back to the junction box, and plate to the outlet.
Route the new ROMEX® as needed into the new switch or outlet's junction box.