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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.

Step 1: Materials

For the Mad Scientist Extension Cord you will need:

(x1) 3PDT 100A knife switch
(x1) Cord end plug
(x1) Cord end socket
(x1) 25' heavy duty fabric cord
(x2) Zip ties

<p>Please be aware, for citizens of the United Kingdom, should you reproduce this design and someone is injured as a consequence, <strong>you </strong>will be held liable and may be prosecuted under the law.</p><p>.</p><p>Some points to note;</p><p>1. The originator is using the switch to break the current flowing to a heavily inductive load increasing the risk of exposure to localized arcing/flash-over.</p><p>2. The switching mechanism is designed to be mounted on a fixed vertical platform (a switch board/panel or wall). As you can see from the animated gif the device jumps as the retaining friction is overcome, resulting in the hand of said individual coming perilously close to the exposed conductors.</p><p>3. The switching enclosure is meant for a fixed cable loom, presumably single core, hence there is no strain relief on the cables. Mandatory in the UK on portable appliances. </p><p>4. The device itself doesn't conform to any BS standards or have a CE mark and therefore has no place in the UK.</p><p>5. The device breaks the earth connection at the same time as the Live and Neutral conductors. Unbelievable!</p><p>6. Cables within the device run the very real risk of becoming trapped beneath the switching blade edge given they are not anchored further increasing risk of injury.</p><p>7. Once located in the 'on' position, live conductors are exposed and un-shielded.</p><p>.</p><p>Quite frankly this article is reckless.</p>
<p>Looks great :)<br>You can coat the handle with some plasti dip to make it much safer.<br></p>
<p>Hey randofo, I've read the safety note but I don't think it justifies publishing a highly dangerous and possibly deadly project on instructables. Your own gif beautifully shows how easy it is to get very close to the conductors. Sure, one shouldn't do anything on the internet without a second thought, but I believe instructables shouldn't skimp on safety for the sake of simplicity for any it's own content.</p>
<p>I am amazed at how many dangerous things get put in this site... For starters it is not considering high voltage.. When talking about AC, then anything under 50V is considered extra low voltage, anything over 50V and up to 1000V is considered low voltage and anything above 1000V is called high voltage. </p><p>In regards to the earth do you realise that the whole reason the earth pin is longer is so it is the first to make contact when it is plugged in and the last to lose contact when it is removed. By switching the earth with that switch it is making and breaking at the same time.. You should never switch the earth like you have in this example, you should have left it permanently wired and bypassed the switch.</p>
<p>Looks cool. It would be safest if the side that plugs into the wall is *not* the side that connects to the middle. I believe this is opposite to how you have it wired, but I cannot be sure. That way when the switch is up out of the block, the copper will not be hot.</p>
<p>I clarify this in Step 10</p>
Looks awesome!
<p>To handle mains voltage, wire this to a low voltage transformer &amp; use a L.V. relay to switch the mains- it should satisfy any code issue.</p>
<p>this is very dangerous , these type of switches should be only used with low voltage 12-24 volts</p>
<p><em>I have always worried about knife switches like these. And I have seen them in the typical Frankenstein movies and thought, wow, what a huge potential for a very bad and potentially lethal shock. What would happen if you made the three prongs from some non-conductive material to merely mimic some type metal and then use a momentary 3PDT push type switch that the knife handles switches underneath? Just an idea and a totally safe way to accomplish everything and still have that nostalgic look.</em></p>
<p>You forgot step 13A: Shout &quot;MUHAHAHAHA&quot; as you throw the switch. Nice job.</p>

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Bio: My name is Randy and I founded the Instructables Design Studio. I'm also the author of the books 'Simple Bots,' and '62 Projects to ... More »
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