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Long and short Madison Bars with old work metal outlet boxes

Installing An Electrical Outlet Box Using Madison Bars

Dear Mr. Electrician: How do I go about installing an electrical outlet box using Madison Bars?  I want to install an electrical outlet on a dedicated circuit for my window air conditioner and someone told me to use Madison Bars to mount the outlet box. Answer: Installing an electrical outlet box using Madison Bars is a simple method for mounting certain types of metal electrical outlet boxes in a wall.  They are also known as Old Work Box Mounts, Support Clips, F Clips, Madison Clips, and Madison Straps.  NOTE: Some text links below go to applicable products on Amazon or EBay. The photo above shows Madison Bars that are two different lengths.  The longer ones are for working in walls that have double drywall or a finished surface such as tile or paneling that makes the wall board thicker. In addition screw clips are shown that can also be used to attach metal outlet boxes to wall board.  They just clip on with a little force.  Once the box is in the wall, you tighten the screw and the clips wedge themselves between the box and the inside of the wall.  You can also buy some outlet boxes with the clips built-in. In the example below the hole was made using a Compass saw.  The metal outlet box was held against the wall and a pencil line was traced onto the surface.  Note the notches on the upper right and lower left corners.  They are to allow for the protruding screws on each side that all gangable metal receptacle boxes of this type have. The boxes are gangable by removing one or both sides and screwing the boxes together with additional boxes to make a multi-gang switch or outlet box.  You can add as many gangs as needed, however the more gangs, the more difficult it will be to find wall plates to cover the finished work. You can special order larger wall plates from an electrical supply company, but you may be limited in the choice of colors and styles. For the hole above I held the face of the electrical box against the wall and penciled an outline to follow with my Compass Saw. INSTALLING AN ELECTRICAL OUTLET BOX USING MADISON BARS The ground wire above is attached to the box using a separate 10-32 ground screw.  Consult Article 314 in the National Electrical Code for the correct size electrical box needed for the amount of wires and devices that will be contained within. It is important to have the hole cut exactly right when installing an electrical outlet box using Madison Bars.  If the hole is too big the ears on the electrical box will not hold against the wall as the Madison Bars will pull the box inward. The ideal location for the new outlet box is next to a wood wall stud.  In that scenario I will drill a 3/16" hole about midway back on the side of the outlet box that will be against the wood stud.  After I install the Madison Bars securely...
A metal outlet box installed on wood lath using small wood screws.

Install Outlet in an Existing Wall

Dear Mr. Electrician: I want to install an outlet in an existing wall on a dedicated circuit for my window air conditioner?  I've got it figured out how to run the 12/2 NM-B cable from the main circuit breaker electrical panel in the basement up through the wall under the living room window.  How do I install an electrical receptacle box in the wall that will contain the wire and support the receptacle? Answer:  To install an outlet in an existing wall requires a lot of measuring.  Assuming that you will be drilling a hole from below and fishing the cable into the outside wall, the best place to cut a hole and mount a box is adjacent to a wall stud.  That way the electrical box can be screwed through its side directly to the wood to make it solid.  NOTE: Some text links below go to applicable products on Amazon or EBay. LOCATE WALL STUD TO INSTALL OUTLET BOX Locating a wall stud may not be that easy.  I usually use an existing wall receptacle or switch as a reference.  If they were installed at the time that the house was built, then they are most likely mounted on wall studs. I would remove the wall plate from the existing receptacle or switch and poke a long thin screwdriver to the right and to the left of the electrical box.  I would also push the box a little to see if it pivots.  Usually the side that is mounted to the stud will not move. In newer homes with drywall I also look for indications of nail holes that were spackled over in order to locate wall studs.  After I have a few studs spotted, I measure over to the area where I would like to cut a hole for a receptacle.  In most home construction the wall studs are sixteen inches apart, but that is not always the case. Sometimes wall studs are twenty four inches apart.  On some taller condominium buildings I have found the outside walls to have studs at twelve inches apart.  Measurement is from center to center and I always measure twice.  If I am lucky my measurement will correspond with a spackled nail hole which confirms that I have a stud.  Tool and material list below. One trick I learned from my dad is to measure 48" from the inside corner of any wall.  There should always be a wall stud there because drywall and paneling are 48" wide and need a stud to land their edge on for support and nailing. On older homes with plaster walls it is not as easy to find a wall stud.  There are no indications of nail holes and sometimes outlets have been installed in the baseboard molding. The use of electronic stud finders on plaster walls can be limited because of the inconsistencies of the old plaster keys and wood lathe.  In this situation the window itself may be the best indicator.  There should be at least one stud on each side...