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Photos depicting the installation of an electrical receptacle outlet box using Madison Bars.     Click for Home Page
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Install an Electrical Receptacle Box in an Existing Wall Using Madison Bars

Dear Mr. Electrician: I want to install an electrical outlet 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 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: The hole below was made using a drywall 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 metal receptacle boxes of this type have.
I held the face of the electrical box against the wall and penciled an outline to follow with my Drywall Saw.

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Photo of a cut-out hole in drywall for an electrical box to be installed
This photo shows the 12/2 NM-B cable brought into the metal box and clamped.  The ground wire 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.

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Wire protruding through hole in wall with an electrical box attached
The longer end of the Madison Bar steel switch box support is inserted first along side of the metal box.

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Electrical Box with Madison Bar ready to be installed in the wall
With one Madison Bar steel switch box support pinched tightly, the other side of the metal electrical box protrudes slightly from the wall.

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Photo of electrical box partially installed using Madison bars
After inserting the second Madison Bar the protruding edge of the metal electrical box needs to be pushed hard against the wall as the Madison Bar is pinched over. You can use a large flat head screwdriver for this, the bigger the easier.  This ensures that the box will be held in place tightly.  Use needle nose pliers to crimp the Madison Bars tightly against the metal electrical box.

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Madison Bar partially inserted into the wall to support the metal electrical box. Click for next photo
 
The box is held firmly in place by the Madison Bars.  It should not be loose.  Note how the upper and lower screw hole tabs on the box are set back into the wall slightly.  Inside the rear of the box is the bare copper ground wire attached to the metal box using a 10/32 screw.

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Electrical outlet box installed in drywall using Madison Bars with the ground wire attached to the inside of the box using a 10/32 screw
The wires are folded and the GFCI receptacle is pushed into the box.

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GFCI receptacle has wires attached and ready to be screwed to the wall. Click for the finished photo
The finishedGFCI receptacle installation using Madison Bars to support the box.  I usually prefer to install the box next to a wall stud so that a wood or sheet metal screw can be screwed through a hole in the box directly into the wood stud in addition to the Madison Bars.  That makes the box extremely secure.  However in this case the customer wanted the receptacle installed in this exact location.

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The finished ground fault circuit interrupter receptacle installed in a bathroom wall using Madison Bars and a metal electrical box
 
Click here for more instructions on installing an electrical box in a wall.

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Updated April 13, 2018

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