Dealing with boxes in ceilings

Light fixtures and fans require an electrical box installed in the ceiling. (Fans are heavy and require special boxes. If you use anything else, the fan might fall out of the ceiling.) An unfinished attic gives you plenty of access to the joist. All you have to do is drill a small pilot hole at the proposed box location into the ceiling from below and poke a section of metal hanger up and into the attic (check the approximate location in the attic first for obstructions and wires). This will enable you to see if there are any obstacles in the attic such as existing wiring or framing that might be in the way of a box. Once you’ve established that the location will work, you can either …

• Cut the round hole for the box with a hole saw.
• Use a keyhole saw or a drywall saw for cutting the hole.

Ceiling boxes can be either nailed to a joist or attached with bar hangers. Nailing to a joist is simpler, but your light might fall between two joists and thus require hangers.

How to deal with plasters?

Plastering is quite a craft. Older plaster jobs consist of three coats of material applied over wood or metal lath. Some old plaster (Victorian homes come to mind) is a little on the crumbly side. If you’re careful cutting through it, you’ll keep your repairs to a minimum.
To cut through plaster …

1. Determine the location of your new box (next to a stud if possible, but do your initial cutting at least a few inches away to make sure nothing gets in the way of the saw blade).
2. Place a drop cloth or a piece of plastic on the floor.
3. Drill a test hole so you can determine where the edge of the stud is located. (Ignore this if you’re not going to be near a stud.)
4. Place the front of your new box against the plaster, and use a pencil to draw around it (ignoring any plaster ears) to give you a line to cut into. You can apply masking tape around the outline to help keep the plaster from chipping when you cut.
5. Drill a hole in each corner to provide starter locations for the keyhole saw or scroll blade.
6. Hold a straightedge against the pencil lines, and score the plaster several times with a sharp blade.
7. Carefully saw through the lath in smooth movements. Go through about 7/8 of the way on one side and then cut the other side completely, returning to cut the remainder of the first side. This prevents the lath from excessively shaking the plaster.

If you have metal lath, you can’t really saw through it. You can try to chisel it out, but this can cause further cracking if you’re not careful. I’d just drill as many holes as you need, following the pencil outline to minimize the chiseling. Once the metal lath is exposed, cut through it with tin snips and smooth out the plaster with a saw blade or a rough file, or tap it with a small hammer.

How to deal with walls?

Running cable through finished walls or ceilings is a nuisance. Once you’ve determined that a circuit can be extended or a new one added, you should plan the circuit’s route and figure out the least-disruptive route for the cable. An existing circuit can be extended from an electrical box provided that …

• The box is sized to accommodate the additional cable.
• The box isn’t at the end of a switch loop (an end-of-the-run switch).
• The box isn’t a switch-controlled receptacle (unless you want the added device to be controlled by the switch as well).

Your best and easiest route is through an unfinished basement or attic, If you’re drilling into a crawl space, place a flashlight over the top of your drilled hole and turn it on. This makes it a lot easier to find the hole when you’re crawling under the house. If you have several holes to drill, insert a piece of scrap neutral wire into the hole; you’ll be able to see its white insulation more easily and mark each hole. It isn’t always easy to determine the location of a box when you’re up in an attic or down in a basement. From an approximate location in an attic, you can drill a very small hole on the outer edge of the wall’s top plate through the ceiling below and then poke a section of wire hanger or scrap wire through. From the room below, you can locate the necessary drilling location, go back to the attic, and adjust your coordinates. From the basement, you can drill a pilot hole from above (if you’re adding a receptacle) through the sole plate or bottom plate of the wall using a long, narrow twist bit. Then drill the larger hole from below. If the floor is only covered with subflooring material such as plywood, you can use your drill or drive a 16d finish nail through a location near the base of the wall where your new box is going in, looking for the nail down below. If you don’t object, you can do the same through carpet; just be sure to place the nail near the very edge of the baseboard and use a nail set to pound the head below the surface of the carpet
What if you have wood flooring? If you cannot accurately determine where to drill from the basement, drill the smallest hole possible (with a drill bit about four inches long) near the edge of the baseboard. Push a piece of wire through the hole so you can find the location in the basement. A piece of scrap conductor from your NMB cable will work just fine. At the end of the job, fill in the hole with a putty stick in a color matching the floor stain.