How to Divide a Circuit When Wiring a House

Turn off the electrical power to the supply line circuit. Mark the breaker to indicate to others that it must remain in the "Off" position.

Check the supply cable wiring to ensure the power is off using a voltage tester. Place the test probes on the tips of the black hot wire and the white neutral wire.

Insert the 12-2 grounded ROMEX® branch cable into the slotted hole of the supply line J-box. Pull approximately 4 inches of the cable into the box.

Remove 3 inches of sheathing from the supply cable and the branch cable with a utility knife.

Remove 1/2 inch of insulation from each wire using wire strippers.

Connect the black hot wire from the supply wire to the black wire of the branch circuit with a wire nut. Tighten the nut clockwise by hand.

Connect the white neutral supply wire to the white branch wire using a wire nut.

Connect the bare copper ground wires together with a wire nut.

Wrap the nuts clockwise with electrical tape. Overlap the tape onto the insulated wires.

Tag the branch circuit wires for future identification. Indicate which is the supply line from the main panel and where each of the branch circuits are used. Masking tape and a permanent marker can be used for this purpose.

Push the wires neatly into the J-box and install the J-box cover. Tighten the box cover using the appropriate screwdriver.

Mark the outside of the J-box with the marker to indicate which circuits are supplied from it.

If you use a grounded metal J-box, connect a bare copper pigtail from the ground wire connection to the ground post screw in the J-box. Record the locations of the J-boxes you use. If installed between wall studs, ceilings or basements, knowing where they are will be helpful when working around these areas in the future.