I upgraded to a better box after doing this write up so some pics are from the first on and some are from the second.  I did this to have more space between the enclosure and contactors.

There isn't much needed for this build.  Here is a complete list of supplies 



$4.36   1x Steel City 2-Gang 42 cu. in. Square Electrical Box (first build)

$20.00 Safety switch box (Ebay second build)

$4.08   2x Steel City 2-Gang Square Electrical Box

$5.96   4x Dual plug outlets

$0.88   1x Solid face plate cover (size of the larger box)

$5.06   2x Dual plug outlet covers

$2.00   3x 10 and 12 gauge solid core wire  

$0.75   1x Stain relief for power cord

$1.78   2x L mounting brackets

$0.50   6x Wire nuts

$1.15   1x Package if nuts/bolts

$1.75   2x  conduit connector things (not sure of the real name).

$13.97  1x Oven plug


$4.30   1x IEC power connection (optional)

$11.17  1x 2 Pole 40 Amps 120 volt Coil Contactor  


$43.75  Not including the oven plug.

The second build added the safety switch $20.00 and the second contactor that I bought in a large lot of for $6.00 each I was able to get rid of the 1 box, cover and the IEC switch shaving off $9.54 making the total cost  $60.21

The first thing to do is to Wire up the outlets. I tightly wrapped the 12 gauge wire around the 10 gauge, screwed on a wire nut as tight as I could get it.  Then a nice snug layer of electrical tape for extra security.  I opened up my friend's controller and this was how the wires were connected.  It gets tight in the gang box so try your best to keep the wires as short as possible to make it easier to assemble. Loop the wires around the screws on the outlets.  Beside the fact the 12 gauge won't fit in the holes I have heard it is safer to do it this way.  I chose black, red and green wires.  My outlets had one side with a label for white so I hooked up the black to that, and red to the other side.  The green goes to the one on the very bottom.  Standard wire colors white black and green.  If I build another one I would use those colors.

Now you are going to want to do is prepare the boxes.  At the very least you will need to drill 4 holes to mount the contactor, and two holes in each box for the mounting brackets.   I also drilled out 1 hole in each box for the ground.  I chose to have both boxes above the larger one.  It seemed it would be easiest to mount it this way.  You can change up the configuration of the boxes.  Just line them up and punch out three holes in the larger box.  I did the two outside top holes for the outlet boxes and one in the middle on the bottom for the power cord.  Punch out one in each of the smaller boxes.  Using the conduit connector things secure your boxes in the configuration you decided on.  Once the boxes are connected together secure the ground to the boxes.  
Thread the other 2 wires through the conduit, and screw the covers on.  At this point you can set the box aside to start working on the cover face plate.
This step is totally optional.  I added an IEC connector.  These are the power supply cords that ar commonly found on computers and ballast.  I added this because it has a switch so I could easily turn off the lights when I want to work in the garden without having to worry about knocking the lights, or when I need to cook.  I used my Dremel with a cutting disc...well a couple of them to make a rectangle hole for the I IEC.  
I forgot to take a pic close up of the IEC wired up.   It was pretty straight forward I am considering building a new controller if I do I will be sure to get a good one.
Now that the boxes and cover are ready to go it is time to hook up the contactor.  Again the solid core wires are somewhat hard to work with so it is best to keep the wire as short as you can.  Connect the two black wires to one side and the red to the other side.  As I said the extension cord I used ended up having a white black and white cord.  With myself using the black wire on the outlets I connect the white wire to the side with black wires and the black to the side with red wires(after the plug I found out it didn't really matter).  After that grab the cover plate with the IEC and connect the two hot wires to the 120v hook up.  Then connect the ground wires from the IEC and the power cord to the ground bolt.  After that, you just need to bolt down the contactor.  The contactor was hard to bolt down, on top the fact the solid core wire made it hard to get the back bolts secure was difficult.   I ended up using the screws that came with the outlets for the back, and the bolts I bought for the front.  Attach the front cover and the box is ready to go.   
The second box I made has the correct white black and green wires as shown below.
Now the box is complete all that is left is to hook up the oven plug.  The directions were not very clear.  They had 2 set of instructions to hook up but didn't explain what the difference was.  After searching the internet I confirmed that the way to hook them up was to connect the ground wire to the middle, and the other two to either of the two side cables.  Have an electrician check out the box, mount the box on the wall next to your ballasts, and plug in the power cable to the oven plug and you are ready to go.  
As I said before I think a professional controller is the way to go, but if you are on a budget this setup will get you by.  After you have your box going for a day open it up and check to make sure all connections are secure.  Do this again a few weeks in, and then periodicity to make sure it is still all good.  There is no doubt this is can save you money.  Remember to be safe and take all precautions to minimize the dangers associated with our indoor gardens.
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