Electrical Rough-in Tips
Whether your project is finishing a garage or a basement or building an addition, it’s important to get the rough-in wiring done right the first time. We talked with several pros and got advice on drilling holes, installing boxes and pulling cable. With these tips in hand, you’ll work faster, avoid disasters down the road and put a smile on the face of your electrical inspector.
Which electrical box works best?
Either plastic or fiberglass boxes will do the job, and each is completely code compliant. Some electricians prefer fiberglass models because they’re tougher, but others prefer the plastic models because they’re cheaper.
Whatever style you choose, pick box sizes that have a volume of at least 20 cu. in. Dimmer switches and other smart devices are common these days and take up more room in the box than the simple devices of the past. Plus, bigger boxes just make wiring easier, especially if they’re crammed full of wires and connectors. Boxes destined for exterior walls and ceilings must be equipped with a vapor barrier seal.
Special cable staples
Staples (and drilled holes) need to be at least 1-1/4 in. away from the edge of a framing member. In some cases, that means stacking wires on top of one another and using one staple to secure them. Most standard staples can handle two wires. Never install staples over multiple wires unless the staple is approved for it. The staple package should list how many wires it’s rated for. The staple shown here is good for up to four wires.
Auger nits and angle drills work best
A 3/4-in. spade bit will work OK for drilling the holes, but auger bits drill faster and require less effort. Choose a bit like this Milwaukee ship auger bit that will chew through nails. It’s easier to drill straight holes through the studs with a right-angle drill. You can rent right-angle drills by the day, or you could buy an angle attachment for your own drill.
Install plates before pulling wire
Electrical cables need to be set back 1-1/4 in. or more from the edge of a stud or wood-framing member to protect cables from wayward nails and screws. Install steel cable-protection plates over holes drilled closer to the edge. Keep several plates in your pouch while you’re drilling and install them right away so you don’t forget.
Drill straight, aligned holes
Keep the holes straight and at the same height. Pulling cable through several consecutive holes drilled at different angles or heights is difficult because the cable will snag on the sharp edges and fight you the whole time! Straight, aligned holes make pulling cable a breeze.
Pull rolled cable from the middle
Don’t rip open the plastic wrapper on your spool of cable. Instead, lift a handful of coils from the center of the roll and lay them on the floor. Four loops equals about 12 ft. Following this method helps reduce tangles and keeps the cable contained for easier transporting and storage. If you plan to use all of the cable, just neatly unroll the entire spool across the floor (as if it were a garden hose) to avoid kinks, curls or twists in the cable.
Avoid exposed open spaces
The electrical code doesn’t allow exposed wires in open spaces. When cable is installed in exposed areas such as a garage or an unfinished basement, it needs to closely follow the framing members. Cables that span stud spaces or ceiling joists are in constant jeopardy of nicks and cuts, and it’s too tempting to use the cables for tucking, hanging or trapping all of your toys and tools.
Straighten wires before pulling
Pulling cable through holes in framing is a lot easier if you straighten out the cable first. Walk along the length of the cable, straightening it between your thumb and forefinger as you go.
Once you’ve pulled the cable through the holes, push it back a bit 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 cable out of the way of plumbing pipes or ductwork.
Don't over-bend cables
Sharp bends in cable can damage the sheathing and the conductors, which could lead to a fire hazard. Cable should not be bent at more than a 2-1/2-in. radius (about the same as a soda can). Avoid over-bending it by drilling holes 8 to 12 in. above (or below) the boxes so the cable can sweep down or up into the boxes. Also, never pull hard on cable that has a staple on the other end... that's just asking for trouble.
Mark box locations
Before you drill any holes, go around the room and mark the locations for all the outlet, light and switch boxes. Install the switches 42 in. up from the floor (to the bottom of the box), and the outlets up 12 to 16 in. These are typical heights used by pros. But actually, there’s no height requirement. The important thing is to make all box heights consistent. Many pros use the length of their hammer as a guide to mark the location for the bottom of outlets. Check out these other outside-the-box uses for hammers.
The National Electrical Code requires outlets to be spaced within 12 ft. of each other. The idea is that every appliance, lamp or device is always within 6 ft. of an outlet.
Ceiling Fans Need Special Boxes
A regular round electrical box isn’t sturdy enough to support the weight and absorb the vibration of a ceiling fan. Special ceiling fan electrical boxes usually have an additional brace to stabilize the spinning fan. These types of boxes are a heck of a lot easier to install before the drywall is up, so even if there’s a small chance that you’ll replace the light with a fan sometime down the road, avoid headaches and spend a couple extra bucks on a fan box.
Strip Off the Sheathing
It’s easier to strip the sheathing from the cables out in the open before they get shoved into the box. Remember to leave at least 1/4 in. of sheathing visible inside the box. If there’s only one cable entering a box, install it through the knockout farthest from the stud.
Angle Into Corners
There’s often not enough room to drill straight into an inside corner from both sides. This is one time when you’ll have to drill into the stud at an angle. Fishing the cable through will be easier if you keep the holes at the same height. Sometimes it’s not possible to fish a cable through a corner. In those cases, drill up through the double top plate of the wall, and route the cable up over the corner and down the other side.