Like many other contractors, I’ve had to run electrical wires through existing walls from a basement to a second story or attic. Whether you are in the basement looking up or in the attic looking down, it can be tough to visualize the path required to fish a wire. Recalling a high-school science class, I developed a fast, inexpensive method to find the way.
Starting in the attic, I study the top plates of the walls below. When I settle on the area where I want the wire, I drill a 1/2-in. dia. hole in the wall’s top plate. Next, I lower a 2-in. bar magnet on a string into the hole. I can now go to the floor below and, as shown in the drawing, zero in on the position of the magnet with my camp compass. When the compass is horizontally in line with the north pole of the magnet, it will point toward the wall. When the compass points away from the wall, it is in line with the south pole of the magnet. The center of the magnet lies between these two points. If I want to find the magnet from below, I lower it to the bottom plate and use the compass held vertically.
This idea has worked for me in running countless wires, ductwork and piping. To minimize complications, I try to avoid walls that I know to have pipes, ductwork, wiring or insulation in them.
Donald Glennie, Sterling Heights, MI