No Access, Now What?

Finished basements and attic spaces (or service panels located in finished garages) call for a more deft approach to your wiring. You have to decide if you should …

• Run part of the circuit in conduit across the basement or garage ceiling.
• Run conduit on the outside of your house and then into the walls.
• Tear into the walls and ceiling at regular intervals, exposing the studs and joist to run the cable.

Most studs and joist are spaced at 16 inches on center (which means the center of the nailing side of one will be 16 inches from the center of another). The spacing offers predictable nailing surfaces for drywall and interior trim, especially baseboards. If you have no other way of getting into the wall or ceiling, you’ll have to open up the wall on each side of the studs and joist until you’ve reached the locations for your new boxes.

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.

How Much You Can Keep?

Basically, you can retain any and all safe wiring and devices. An electrical system will do what it’s designed to do and will do so reliably until you extend a circuit or the system beyond its design. You should remove or replace the following:

• Any corroded or damaged wiring
• Wiring that has not been installed properly (such as wire running along the bottom edge of an exposed joist rather than through holes drilled in the joist)
• Devices or fixtures that render a circuit unsafe
• Conductors that are the wrong gauge for their circuits
• Any cable rated for interior use but installed outdoors You might be getting more than you bargained for if your system has been repeatedly altered over the years.

If additions have been made based on convenience (“Hey, look! I found a couple of wires.”) rather than logic, you could end up with an odd variety of lights, receptacles, and other fixtures all over your house. It might be best to run a new circuit or two to cover all these miscellaneous runs if you’re not already rewiring the whole house.

Mixing Old and New Wiring

You can connect new cable or wire to existing cable or wire if you follow these rules:

• All connections must be made inside an electrical box. The one exception is knob-and-tube wiring, which is the only electrical system that can be spliced in the wall. To do so, you must solder the conductors or use a mechanical splice such as a split bolt; a wire nut is not sufficient.
• Junction boxes must be kept accessible. They cannot be covered up.
• Don’t change the wire gauge. (New wire has to match existing wire.)
• Be careful not to overextend the circuit by adding more loads than it’s designed to handle.

Knob-and-tube wiring doesn’t lend itself to easy identification of the hot and neutral conductors. You might have a junction box or device box packed with wires. Identify the hot lead the same way you would identify it in a less-crowded box:

1. Identify the circuit and turn off the power at the panel.
2. Check the connections with a voltage tester to confirm that the power is off.
3. Carefully remove any tape or wire nuts from the connected wires (those running back toward the panel).
4. Mark the wires so you know which ones were connected to each other.
5. Separate the wire ends so they’re not touching each other or the sides of the (metal) box.
6. Turn the power on at the service panel and test the wires one at a time until the hot lead lights the bulb on the tester.

Mark this as the hot line conductor. Messy junction boxes often indicate that a device or fixture was added without a lot of consideration as to its effect on the circuit. Your best bet is to confirm whether the circuit can or cannot safely support the addition and then deal with it appropriately. It might be that all you’re looking at is an unkempt, but safe, series of connections.

Messing Around With Old Wiring

The easiest residential wiring to work with (short of metal conduit, which you’ll never find in a typical home) is grounded NMB copper cable. It’s newer than knob-and-tube wiring, the insulation is tough plastic, and you have none of the safety dilemmas that you have with aluminum wiring. If your electrical system was recently installed and inspected, it should be simple to trace circuits and calculate loads as you plan your additions and changes.
Regardless of the age of your system, you’ll have to tally your amperage usage for the total system as well as for each individual circuit affected by your work. Simply looking inside your service panel and counting the breakers or looking for an empty space to install a breaker isn’t enough. Wiring or changing your system generally means doing some damage to your house.
The larger the access holes and openings for boxes, the more repairs you’ll have to do. Your working goal should be to keep the repairs and patching to a minimum. As you can see, there’s more to electrical work than simply deciding to add a receptacle and running some wire.