How to install a new circuit; connect to the service panel

Before you install a new circuit in your house, check with your local electrical inspector about the materials and procedures required to meet electrical code requirements. Buy cable, breakers, connectors, ceiling and junction boxes, and receptacles as he advises.

Readying cable for connection Shred 8 inches of plastic sheath from the ends of an NM (nonmetallic) cable with a ripper; cut off shreds with a utility knife. If you’re using BX cable (wires cased in a flexible spiral of galvanized steel), cut through one spiral at a right angle with a hacksaw. Firmly grasp the cable at either side of the cut and twist it apart. Unwrap a couple of turns of paper directly under the armor; rip it off. Bend the copper grounding strip over the outside of the cable. Push a fiber bushing into the cable end to its sharp edge from cutting the wire insulation and causing a short circuit. Strip 3/4 inch of insulation from each wire of the NM or BX cable with wire strippers.

Your cable must reach from the service panel to the first new outlet; splicing is not permitted. If you’re running the cable along rafters, joists, or studs, staple or strap it fast or run it through 5/8-inch holes.

If you’re running the cable behind a wall, you’ll need a fish tape, a 25- or 50-foot reel of flattened steel spring wire. Drill holes into the wall, floor, or ceiling so that you can fish the cable from one location to another. Loop the stripped ends of cable wires over the fish-tape hook, then secure the bond with electrician’s tape.

Installing a junction box

Make a template of the box (minus its ears and mounting plate) by placing it facedown on a piece of cardboard. Pencil this outline on the plasterboard wall, then cut it out with a utility knife. Secure the box with bracket tabs. Screw the plate holes to the wall.

In a plaster-and-lath wall, locate the studs; plan to install the box on the lath away from studs. Use a hammer and cold chisel to chip away enough plaster to fully expose a wooden lath strip. Make a template (including ears) as described. Pencil the outline so that the box will be centered on the lath. Drill 3/8-inch holes for screw tabs at two diagonal corners of the outline. Insert the tip of a keyhole saw into one of the holes and saw out the pattern. (Use a saber saw with a metal-cutting blade to cut through a metal lath.) Adjust the ears of the box and mark screw holes on the lath for securing the ears; drill the holes.

Slip a cable connector onto the end of the cable sheath; screw it fast. (Skip this step if the box is equipped with cable clamps.) Using an old screwdriver, push in a knockout hole in the box, then feed the cable end through this hole. Fit the box into the wall so that it is flush. Screw the box onto the lath, then secure the cable connector to the box. Patch the plaster around the box. Wire the receptacle, then screw it to the box.

Connecting to the service panelĀ 

First turn off the main breaker; this shuts off all circuits. With a hammer and nail set, remove the central ring of a multiring knockout from the panel; pry up the next ring by levering a screwdriver with pliers; pull off the pried-up ring sections with pliers. After you have secured a connector to the cable sheath, flush to the stripped edge, connect the cable to the service panel through the knockout hole. If the panel’s breaker space is limited, replace a standard breaker with a piggyback to which the leads of the old circuit and the new can be wired, or use two skinny (half-size) breakers.

Attach the bare ground and white wire to the ground bus, and the black wire to the piggyback breaker; screw them fast. Don’t turn on the new circuit until it has been checked by an electrical inspector.