This story shows how to easily and accurately measure drywall cuts for electrical boxes.
Some people believe that accurate results require tedious measurement. But this procedure demonstrates how easy it is to get great results without squinting at a tape measure. In fact, once you've made the jigs for setting and marking the boxes, you can put your measuring equipment back into your toolbox.
The box-setting jig enables you to quickly position outlets at a uniform height and with a consistent projection from the framing. You then use the marking jig to transfer the position of each box to the floor, virtually guaranteeing that you'll never bury a box behind the drywall.
The marking jig then enables you to lay out the box's outline onto the face of the panel. Cutting the opening with your jab saw is a quick and confident process.
Allow approximately 5 minutes per outlet box for setting, marking, and cutting
Circular saw to make jigs, power drill/driver, jab saw, pencil, fine-line permanent marker
Measuring and marking, using the jab saw
Wiring must be installed and inspected, if required by local regulations.
Plywood, 2x4, screws
Make the jig for setting electrical boxes, and use it when you nail the boxes to the studs to ensure uniformity. Rest the box atop the jig, and position its front edge flush with the plywood. After the wiring is completed (and inspected if necessary), install any other utilities behind the wall and add insulation if desired.
Cut a square of 3/4-inch plywood that matches the height of the top of the electrical boxes. Mark the bottom of the box on the plywood's edge. Use this jig to transfer the position of each electrical box and switch onto the floor. The circle with two lines drawn on the floor is the symbol for an outlet. A dollar sign is the symbol for a switch.
Attach the drywall to the studs, but avoid any fasteners within 16 inches of each box. Using the plywood jig and the marks on the floor, draw the perimeter of each electrical box onto the drywall. Align the edge of the plywood with the right mark, and draw a pencil up the edge of the plywood and over its top end. Hold the pencil at the lower mark on the plywood, and slide it to the left until you reach the left mark on the floor. Draw up the edge of the plywood to complete the perimeter of the box.
Use a jab saw to cut the opening for each box. Cutting about 1/8 inch outside of each line creates enough clearance so that the drywall will fit easily. Pulling the edge of the drywall slightly away from the wall allows you to saw with a longer stroke. Keep the cut square to the surface of the drywall, and be careful that you don't snag any wires or nick the electrical insulation.
Sometimes the aesthetics of a room or convenience dictate that an outlet box must be at a precise location that's not immediately next to a stud. Although you can solve this problem by adding framing members, an "old work" electrical box is an efficient answer.
First, run the wiring to the stud bay, and coil an extra length of wire to make it easy to grab later. For safety, cap each conductor of the wire with a separate wire nut or tape. After you attach the drywall, cut a hole for the box. You can trace the outline of the box onto the wall or get a free paper template from the store where you buy the electrical box.
Pull the wires through the hole, thread them into the box, and set the box into its opening. Rotating the mounting screws of the box turns ears that press against the back surface of the drywall to securely hold the box.