The Mad Scientist Extension Cord uses a monster movie style knife switch to turn power to the extension cord on and off. I like using it to turn my Jacob's Ladder on and off. This whole setup consists of a heavy duty 3PDT knife switch and 18 AWG 3 conductor fabric wire that is rated for up to 5A of current.
The high voltage might make this seem complicated, but it is a rather simple project. In fact, we are only wiring up half of the switch's connections, such that is wired more like a 3PST switch. Ultimately, it is just an extension cord with a switch in the middle. We are simply extending the three prongs from the wall socket and making or breaking each of three connections.
While this is simple, I'd once again like to point out that the electrical contact from the wall is slightly exposed, and there exists a real chance of electric shock if used wrong. You will need to be careful when handling this, and it is not good to leave plugged in anywhere you may have children, small animals or people who don't understand electricity. Since I have just described most places, it is not recommended you keep this plugged in when not actively demonstrating it. In fact, is likely in violation of most building codes in most places, so this is only a novelty item that you should always be careful when handling, and never leave plugged in or unattended. But it's great for your Halloween Haunted House display, or for impressing house guests.
To learn more about electricity and switches, check out the Electronics Class.
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Step 1: Materials
Step 2: Remove the Cover
Remove the half of the cover which exposes most of the screw terminals for the center electrical contacts.
Step 3: Widen the Hole
We need to widen the center hole of the cover to allow the fabric cord to be cleanly inserted.
Since this is a very soft plastic, we can misuse a hand drill drill to cut horizontally and extend the hole.
Insert a 3/8" or 1/2" drill bit and at a medium to high speed gently cut inward to widen the hole.
Step 4: Remove the Insulation
Using a razor blade, box cutter, or craft knife, carefully remove 3" of the outer insulation from one end of a 8' section of fabric cable. Wrap
the cut end of the insulation with tape (preferably the color of the
cable) so it does not fray.
Repeat this process for a second cable.
Step 5: Wire It Up
Strip a little insulation off the end of each of the three inner wires.
Wrap each wire clockwise around a screw terminal, and fasten each one firmly in place.
Which color gets connected to which is unimportant at this juncture.
While you are at it, affix a zip tie to the end of the cable (around the tape) and trim away most of the tail. This zip tie will be used to prevent the cord from being able to fit back through the hole in the cover.
Step 6: Fully Uncover
Remove the second half of the cover.
Step 7: Remove the Center Screw
Remove the center screw from the other outer set of screw terminals. This will allow you to easily pass the cable through later.
Step 8: Finish the Wiring
Strip insulation of the three inner wires of the remaining cable.
Connect these wire to the center terminals such that wires of the same color are aligned with one another.
Attach a zip tie to this cable near the edge of the switch and cut off most of the tail. Again, this is meant to prevent the cable from being pulled free from the switch.
Step 9: Case Closed
Put the protective covers back on while ensuring the zip tie attach to each cable is on the inside of the covers.
Step 10: Wire the Socket
The last thing left to do is to attach the socket and plug to each end of the cable. The socket should go to the end connected to the center
terminals. This is very important to
get right because if you do this backwards, the center bars of the
switch will always be hot, which increases the likelihood of electric
Anyhow, disassemble the socket and pass the cable through its casing.
Strip away about an inch and a half of the wire's outer insulation, and then strip a half inch from the ends of the inner wire. Insert each of them into one of the screw terminals in the socket. The wire color is not important, so long as it ultimately matches the wiring on the plug.
Finally, wrap the end of the cut insulation with tape to keep it from eventually fraying.
Step 11: Wire the Plug
Repeat the wiring process for the plug, making sure you attach the inner color wires identically to the plug as you did the socket.
You can ensure you got it right by inserting the extension cord's plug into its own socket and seeing if the color wires line up.
Step 12: Close Up the Cases
Once the colored wires are all aligned, close both of their cases back up.
The plug and socket should be assembled and it should now be complete.
Step 13: Let 'er Rip
When it's done, plug something in and throw switch (kuh-chunk!) to turn it on. It works well for dramatic effect with either of the projects
from the previous lesson. Don't forget not to leave it unattended.
Also, if you liked this project, don't forget to check out all of my other Instructables.