Basement Power/Water: Wiring in Masonry Walls

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Because it's difficult to run wiring and install boxes on masonry walls, it may be easier to build secondary walls against the foundation and run wire through them. However, if wiring directly onto the masonry walls makes sense, read the following step-by-step project. Be sure to check local codes, particularly when it comes to grounding the metal parts of the system.

Installing Surface-Mount Systems

Wiring can be routed along the surface of a concrete or concrete block wall as long as it's contained in a system that protects the wires from mechanical damage. One system calls for the use of metal boxes and thin-wall metal conduit called EMT.

Special connectors form a tight seal between box and conduit. Conduit is secured with metal straps that are screwed to the masonry. Electrical boxes also are screwed in place. Installing the system calls for special tools, and because sheathed cable is too bulky, individual wires have to be pulled through the conduit.

Installing Surface-Mount Systems. Individual conductors are routed through lightweight metal tubing that's connected to each electrical box.

A similar surface-mount system is easier for do-it-yourselfers to install. Instead of metal conduit, it uses plastic track with a snap-on cover to contain the wire, along with a series of fittings for changing direction and splicing lengths of track together. (Check local codes before installing this kind of system.) The only special tools needed are a hacksaw and an electric drill and carbide bits. The system itself can be purchased at home center stores. Make a sketch of the basement that shows approximately where switches, outlets, and fixture boxes will be installed, and bring it shopping with you. If the supplier allows unused materials to be returned, purchase more supplies than you think are necessary.

1. Installing the Power Feed. Surface-mount systems use single conductors rather than sheathed cable. Sheathed cable, however, can be used to connect the surface-mount system to the service panel. A special adapter plate that fits over a standard electrical box makes the transition from sheathed cable to individual conductors. The surface-mount box contains cutouts in all four sides of the box to accommodate track that goes up, down, or to the side.

2. Installing Channels and Elbows. Begin at the starter box, and install lengths of base track (available in 5-foot lengths). Drill a hole through the base track every 18 inches and inch from each end. Then use it as a template for marking holes on the wall. Drill holes in the wall for concrete screws or plastic shields; then screw the base track to the wall. (Be careful not to tighten screws so much that they damage the track.) Route the base track to the area of each switch and outlet box, and secure the box with concrete screws or plastic shields according the manufacturer’s instructions.

3. Installing Intersections. In the places where lengths of base track intersect mid-run, cut away the lip of the track to make room for wires. Tracks that intersect at an inside or outside corner are butted together. Turns on the same wall are mitered. Use a hacksaw and a miter box to make the cuts.

4. Running Wires. Surface-mount systems use type THHN conductors instead of sheathed cable. As many as ten 14-gauge conductors can fit in a channel. (Only seven 12-gauge conductors fit.) Use plastic clips to hold wires that stretch from switches to boxes.

5. Capping the Base Track. Cut lengths of base-track cover to fit over the base track, and snap them in place. Cut covers 1 3/8 inches short of each intersection to accommodate the various joint covers.

Attach an adapter plate to the existing box. Then install a surface- mount box, and connect the surface-mount track to it.

Drill holes in the base track. Use the track as a template for marking holes in the masonry.

For mid-run intersections, cut away the lip as shown. Use butt joints for inside and outside corners; miters for turns on the same wall.

Route individual conductors to each switch, outlet, and fixture served by the surface mount track.

5--Covers snap over the base track while joint covers snap over intersections and seams. Conductors are not visible when the installation is complete.

Relocating Existing Wiring

In most cases, a great deal of wiring already exists in the basement. These wires feed circuits elsewhere in the house and may have to be moved, depending on where they are and what is planned for the basement ceiling.

If wires run through holes in the joists, there is no need to worry about them unless they come closer than 1 1/4 inches to the edge of a joist. If so, nail a protective metal plate to the joist to prevent the wires from being punctured by nails. If a suspended ceiling is to be installed, the wires don't have to be relocated. However, if a drywall ceiling will be installed and wires run along the underside of the joists, the wires must be relocated.

1. Loosening the Wires. Use nippers to grasp the edge of each cable staple, then lever out the staple. As you do this, don't crush the cable beneath the nippers, and don't nick the outer casing of the cable. Move the wires aside temporarily and dispose of the staples.

2. Cutting a Notch. According to building codes, notches in the bottom of a joist must be no more than one-sixth the depth of the joist, and they must not be located in the middle third of a joist’s length. If you can’t meet these criteria, disconnect the circuit and run the wires through holes in the joists. To lay out the notch, set an adjustable square to the depth of the notch (making the notch just deep enough to contain the wires), and mark cut lines on the edge of each joist. Use a saber saw or hand saw to cut both sides of the notch.

3. Completing the Notch. The bottom of the notch will be parallel with the grain of the joist so that the waste wood can be knocked out easily by striking it with a hammer. If necessary, use a chisel to clean up the bottom of the notch.

4. Relocating the Wires. Move wires into the notch. (If necessary. use a cable staple to hold them.) According to electrical codes, the wires must be protected by a metal plate that's at least 1/16 inch thick.

1 - To remove a cable staple, grasp one side with flippers and pull out the staple. Do not damage the cable itself.

2 - Never notch a joist in the middle third of its length. Mark cut lines for notches where cable crosses each joist, and use a saber saw or hand saw to make the shallow cuts.

3 – Strike Notched area with a hammer.

4 – Move wires into the notches, and nail a protective metal plate to the edges of the joist.

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Updated: Tuesday, June 4, 2013 23:33