How to Rough-In Electrical Wiring | The Family Handyman

Do-it-yourself guide with professional techniques for a safe wiring job.

Plastic boxes and flexible nonmetallic cable (commonly called Romex) put electrical wiring projects within the skill range of every dedicated DIYer. In this article, well show you some house wiring basicshow to position outlet and switch boxes and run electrical cable between them. We wont cover many other house wiring details. For help with circuit design and making connections to your main electrical panel, we recommend you consult a licensed electrician.

Besides standard hand tools, youll need a special-purpose tool to cut and strip electric wire. We like the Klein No. 1412 ($18 at hardware stores and home centers). To drill a few holes, use a 3/4-in. spade bit in your electric drill. For larger jobs, rent a heavy-duty right angle drill ($25 per day) and equip it with a 3/4-in. x 6-in. auger bit ($7).

Electrical house wiring mistakes can be deadly, so make sure you obtain a permit from your local building department and have the work inspected when youre finished. Draw a sketch of your room that shows lighting, switch and outlet locations. Review your plan with the inspector and ask whether there are any special requirements.

Measure and mark the center of each box. Use letters and symbols to identify boxes. Add 24 blocks to position boxes away from wide window and door trim.

Position the box so its face will be flush with the wall covering material. Then nail the box to the framing. Double check that the face of the box is parallel with the framing member.

Adjustable depth boxes cost about $2.

First mark the box locations on the studs (Photo 1) using symbols to indicate outlets, switches and lights.

O// = Duplex receptacle; S = Single switch; S3 = Three-way switch;O+ = Light fixture.

Mark the height from the floor to the center of the boxes (usually 48 in. for switches and 12 in. for outlets) or line them up with existing boxes. Then nail up the boxes so the face of the box will be flush with the face of the future wall covering (Photo 2). Most boxes have nibs or marks to help you align the box for use with standard 1/2-in. thick drywall. If youre not sure how thick the final wall material will be, use a special adjustable depth box. Paddle fans require a special box assembly that is rated to support the weight and stress of a spinning fan (see Special Boxes, at the end of this story).

The electrical code limits how many wires you can safely put in an electrical box. To figure the minimum box size required by the National Electrical Code, add:

1 for each hot and neutral wire entering the box1 for all the ground wires combined1 for all the cable clamps combined (if any)2 for each device (switch or outlet-but not light fixtures)

Multiply the total by 2 for 14-gauge wire and 2.25 for 12-gauge wire to get the minimum box size required in cubic inches. Plastic boxes have their volume stamped inside. Steel box capacities are listed in the electrical code.

Bore 3/4-in. holes through the framing members about 8 in. above the boxes. Center the bit on the stud, brace the drill and apply pressure with your thigh for easier drilling of wall studs.

Angle the bit into tight spots. Eyeball the angle to make sure theres at least 1-1/4 in. between the back face of the stud and the cable (Fig. A). Then cover the face of the stud with a metal nail plate to protect the cable where the hole is closer than 1-1/4 in. to the face of the stud (Photo 6).

Rough-in wiring detail.

3/4 x 6 auger bit

With the boxes nailed up, youre ready to drill holes and pull cable. The holes and the cable running through them must be at least 1-1/4 in. from both faces of the stud to prevent nails and screws from hitting the cable (Photo 3).

This means drilling dead center on 24 walls. If you have to drill closer to the face of the stud, protect the area with a nail plate (Photo 6). When you drill floor or ceiling joists, drill toward the end rather than the middle of the span, and keep the holes centered on the width of the joist. You can easily pull two 14-2 or 12-2 cables or one 14-3 or 12-3 cable through a 3/4-in. hole. Drill more holes for additional cables.

When you drill through wall plates (the horizontal framing members on the top and bottom of the wall), keep the hole a few inches from the stud to avoid hitting nails.

Straighten about 12 ft. of cable and thread it through the holes from one box to the next. When you reach each new box, follow the stripping procedure shown in Photo 7, push the conductors and about 1/4 in. of sheathed cable into the box, and staple the cable (Photo 8). Then cut the end still connected to the coil and repeat the process at the other box.

Fish the cable around corners by bending a sharp hook in it. Then stick your little finger into the hole to feel for the cable and guide it through as you apply pressure with the other hand.

Grab the cable at the point you estimate it will enter the box. Cut the cable about 12 in. beyond this spot and strip off all but about 1 in. of sheathing.

Stripping tool, Klein NO. 1412

When youre done drilling holes, pull the cable between the boxes and to the service panel to complete the circuit. Start by pulling about eight loops from the center of the coil and tossing them away from you. Then pull the 12-ft. length of cable back between your thumb and forefinger to remove the twist and straighten it out. The whole process takes only a few seconds and keeps the cable from twisting and kinking as you pull it through the holes (Photo 5).

Once youve pulled the cable through the holes, push it back a little to leave a small amount of slack. This is handy insurance in case you cut the cable a little short and need extra length, and it also allows other tradespeople a little slack to push your wire out of the way.

Photo 6 shows one method of getting the cable around a corner. But keep in mind that its often faster and easier to drill up through the double top plate of the wall and route the cable up over the corner and down the other side.

Remove about 12 in. of the white outer plastic sheathing from the cable before you push it into the box (Photo 7). Use a stripping tool like ours for 12-2 and 14-2 cable, or an inexpensive ($2.50) sheathing stripper that works on all cables. You can also use a sharp knife to slit the sheath, but if you nick the insulation on the electric wire, cut the cable off at that point and try again.

Push the cable into the box so that at least 1/4 in. of sheathing is visible inside the box. The National Electrical Code requires that at least 3 in. of wire protrude beyond the face of the box, but we recommend at least 6 in.

Position outlets so that no point in any wall space is more than 6 ft. from an outlet without crossing a doorway. Install an outlet in every wall section thats 2 ft. wide or wider.

Heres what electrical cable looks like inside.

Punch a hole (or two for two cables) through the knockout area of the box with a screwdriver or the point on your stripping tool. Push the conductors and about 1/4 in. of sheathed cable into the box and staple the cable within 8 in. of the box. The cable must be at least 1-1/4 in. from the face of the framing. Push the first cable aside while you staple the second cable.

Run cable(s) from your completed circuits to the service panel. Leave 4 extra feet of cable for the electrician to work with. Label the cables with the location of the circuit. Then call in the electrician to connect the circuits.

Next staple the cable in place. Position the staples in the following locations:

Because cables must be kept at least 1-1/4 in. from the face of studs, you cant staple them side by side along a 24. The electrical code also prohibits you from placing more than one cable under standard 1/2-in. staples. Instead, weave the cables (Photo 8) or use special cable stackers.

For safe wire connections, cut all the wires to leave at least 6 in. protruding past the face of the box. Leave one bare copper ground wire an extra 6 in. long. Thread the long ground wire through the hole in the top of the special green wire connector and splice all the ground wires by holding them together and twisting the connector clockwise until its tight. Strip the ends of the white and black wires and one end of each 6-in.-long pigtail and splice them with wire connectors. Cover the unstripped end of the black (hot) pigtail with a wire connector for safety.

Group and label the wires in the switch boxes so youll know how to connect them after the drywall is complete.

Fold and pack the wires neatly into the box to conserve space and reduce pressure on connections. Label wires with scraps of cable sheathing.

Complete the rough-in phase of the wiring job by connecting the appropriate wires with wire connectors, adding short lengths of wire (pigtails) where theyre needed and folding all the wires neatly into the boxes.

Photos 11 and 12 illustrate a number of important concepts and handy tips for making up any box. In addition, follow these guidelines:

Protect the cable in 1-1/2 in. or thinner walls by running it through 1/2-in. metal conduit. Anchor a 4 x 4 x 1-1/2 in. metal junction box and attach a length of conduit to it with a conduit connector (youll need two conduits for two cables). Secure another conduit connector to the top of the conduit to protect the cable from the sharp edge of the pipe. Secure the conduit with a conduit strap. Attach the ground wire to the metal box with a ground screw driven into the threaded hole. Finally, cover the box with a plaster ring that matches the wall covering thickness.

Special box: Paddle fan box with bar hanger

Special box: Light fixture or paddle fan box

For an average-size room, youll be able to buy all the electrical rough-in supplies youll need at hardware stores or home centers for less than $100. Heres what to buy:

Have the necessary tools for this DIY project lined up before you startyoull save time and frustration.

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How to Rough-In Electrical Wiring | The Family Handyman