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Electric switches, when approached with the correct safety precautions, are simple to install. You should always remember that prior to working on a switch you should turn off the power to its circuit. To insure that the switch has no power coming to it, unscrew the cover plate and mounting screws then carefully pull out the switch. Using a neon test lamp, touch one probe to the metal on the shell of the box, then the other probe to another and finally to the terminal screw. The bulb that works on the switch should not light in either position.

On the most common switch, which is called a "middle of the run" switch, two either black or black and red hot wires will be attached to the brass terminal screws of the switch. Begin by loosening these screws and disconnecting the wires. It is not necessary to disconnect the white neutral and bare grounding wires, so they can stay in the box as they are. To test the switch you should attach the alligator clip of a continuity tester to one terminal and the probe to the other. Next, turn the switch on and off while watching the tester light. The light should only be lit when the switch is on. Then attach the clip to the mounting bracket and the probe to another mounting bracket. The probe should also be attached to one of the terminals and then the other terminal. When you turn the switch on and off the tester should not light in either position.

If you get inside the switch and the wires are different than the ones described above, it is possible that your switch is "an end of the run" switch. In this case, one black and one white wire will be attached to the terminals. The white wire is hot on this switch, not neutral. In some cases the white wire will be marked with black paint or electrical tape. You will need to disconnect both wires in this type of switch before testing the switch in the same manner as above. When you discover that your switch is not working you should always replace it with a switch of the same voltage and amperage. If you are unsure of how to tell what voltage or amperage your switch is, disconnect it and take it with you to the hardware store so you can ask professional advice when making your purchase. When you are ready to install a switch, hook a hot wire clockwise on each brass terminal and then tighten the terminal screws. Look to see if your new switch has a green grounding terminal. If the old switch did not have one, simply run a bare or green insulated wire jumper from the green terminal screw to the wire connector linking the grounding wires in the box. If you discover that the cable serving the box is steel armored, you will need to run the jumper from the terminal to the box's grounding screw. Then you should fit the wires and the switch into the box, reattach your switch to the box, and screw the cover plate back on.

To start from scratch with a switch box you will need to remember that it is necessary to install a new circuit in your house. Begin by checking with your local electrical inspector to find out what materials and procedures are required to meet the electrical code requirements. When you buy your cable, breakers, connectors, ceiling boxes, junction boxes, and receptacles, always follow the inspector's advice. To prepare your cable for connection you should begin by shredding 8 inches of the plastic sheath from the ends of a non-metallic cable with a ripper. Using a utility knife, remove all the shreds. When you are using wires that are cased in a flexible spiral of galvanized steel, or what is know as BX cable, cut through one spiral at a right angle with a hacksaw. Grasp the cable firmly at either side of the cut and twist it apart. Next you should unwrap about two turns of the paper that is directly under the paper and then tear it off. The copper ground strip should be bent over the outside of the cable and a fiber bushing pushed into the cable end to prevent its sharp edges from cutting the wire insulation or causing a short circuit. Strip 3\4 inches of insulation from each wire with a wire stripper and you are ready to run the cable behind the wall.

To install the junction box, place the box with the ears and mounting plate removed, face down on a piece of cardboard. Use the cardboard pattern to draw the outline on the wall. Cut the outline out with a utility knife and secure the box in the wall with the bracket tabs. Attach the plate holes to the wall with the screws provided. It is wise to remember when you are working with a plaster and lath wall to locate the studs so you can install the box on the lath away from the studs. In this case you will need to pencil your box pattern so that the box will be centered on the lath, then drill 3\8 inch holes for the screw tabs at two diagonal corners of the outline. Before you drill the holes, insert the tip of a keyhole saw into one of the holes and saw out the pattern. Next, adjust the ears of the box and mark the screw holes on the lath for securing the ears.

Remember that all switches should be about four feet from the floor when cutting your holes. Next, you will need to remove the knockouts from the box for each cable that will enter the box. Then eight inches of each cable should be fed through each hole. Use the internal clamps to secure the cables at the end of its insulation. The internal clamps should be supplied with your wall box. Attach the stripped ends of the white wires and the bare grounding wires together with wire connectors. Be sure if the box is metal to run a grounding jumper from the grounding wires to the box. Once this is done you are ready to install your switch according to the directions given above.