How-to: Make A Mains Crossover Cable

Update: This How-To was written for April Fools’ Day. It is not advised  you attempt to make or even use this cable. The comments have made it very clear how dangerous to you and others using this cable can be. The image above is not of a full male-to-male cable, only the ground is connected, and the generator is not running.

We all know Ethernet has the crossover cable, cars have jumper cables, and RS232 has the null modem. Well, it is about time our wall sockets get their own crossover cable. This crossover cable is great for running power to a circuit disconnected from power. Maybe you are out of fuses, the breaker is broken or you just don’t want to go check the fuse box when there is a murderer about. This cable makes a great gift for even the most loathsome of acquaintances.

This an April Fools’ Day post. You should not do this!!!

Warning: These are Mains voltages and currents we are working with. If you do not know why you should not attempt this, you should not attempt this.

You will need:

  • 1 Extension cord.
  • 1 Male extension cord repair connector.
  • Tools to strip the extension cord, and attach the connector: Knife, wire strippers, and screwdriver.
  • Respect for mains voltages and currents.

If your extension cord has warning labels, read them.

Cut the extension cord to the desired length.

Strip about one inch (2.5cm) of the outer insulation from the part of the cord that has the male plug.

Strip about 3/8 inch (1cm) of each of the conductors. If there is a strip gauge, use it for a guide instead. Twist each of the stranded conductors to prevent fraying and possible shorts later.

Slide the shroud over the cord.

Screw the conductors into each of their respective terminals on the connector.

  • The Green or bare conductor goes to the ground conductor terminal. It often has a green screw.
  • The White conductor goes to the grounded conductor terminal. It often has a silver-colored screw.
  • The Black conductor goes to the ungrounded conductor terminal. It often has a gold-colored screw.

Use a multimeter to check continuity and make sure there are no shorts.

Slide the shroud up to the connector and fasten the two parts together.

Secure the cable clamp.

There you have it, a finished Mains crossover cable.

There you have it, a Mains crossover cable. How might you use this crossover cable?

397 thoughts on “How-to: Make A Mains Crossover Cable

  1. @Rollyn01

    clearly you have never been around kids. how many times have you told a kid to “dont do that” or “stop that” and they obey your every word every time and never ever do it? kids never like being the guilty one and will often try to rectify the problem trying not to get caught. yes in this case the lights may go out but during the day just with non noisy/illiminated appliances being powered at the time?? Dad could be sitting on the toilet, putting out rubbish any number of things. Like drowning, escaping out the front yard, getting burnt… things with kids happen much quicker that you would expect.

    If you do persist with this sort of life risking practice i’d suggest you plug the lead into an outlet outside the living areas of the house away from anyone to avoid any risk, unlike the photo in the article. even as an electrician i have never made anything nor would i make anything like this and thats not because its illegal. And yes from what i see in my trade these days the world is filling up with idiots, and fast.

  2. @Rollyn01
    electricity kills, it only take one mistake = common sense. so yes i was using common sense. i didnt grab my dads shot gun and say i knew how this works without proper training/instruction either.

  3. so hey i just tried it but it didnt work?

    my fusebox just exploded and as for the generator i think it overheated or something ill try it later but anyway have yuo guys tried this yet?

  4. I know I’m late on this one, but good post!!! Reading through some of these replies, some folks just shouldn’t be on this site………(Brains are for more than just skull fillers)

  5. If you own a boat or RV, you likely have a commercial version of this very thing, only with fancy ends to keep people from frying themselves(usually only one fancy end, on the boat/rv end, unless you’re talking major amps, then it’s twistlock on the power end).

    So, crybabies, shut up. These things have “real” uses.

  6. @Ian

    Yes, I have been around kids. I have my son, who is 2 and a 10 year-old step-daughter. I’d be damn if I told them to do something and they disobey( not that I’d discipline them) because I would explain in the simplest term why not to do it. My step-daughter listens and accepts it, but of course, my son thinks it’s funny and runs to do it. However, I’m usually( and if not me, their mother is) there to prevent anything bad from happening.

    As for hooking it up to an outside outlet, I can definitely agree on that. Hopefully if someone does indulge in this, they know enough to “weather-proof” the situation. I’m also very alarmed and in dismay about people who are learning and/or in a trade who are idiots. I thouhgt for sure they screen and do testing before they start the training phase. Cest la ve, I guess. :|

    You didn’t just grab his shotgun and said you knew what you was doing because you regconized that it’s a dangerous weapon. If you didn’t, you might have done what many others have done out of ignorance( read both uneducated and/or unwilling to be educated), unintentionally harm someone or yourself. Common sense only applies when something is universal. I know that if something hits me fast enough, it will hurt. If I am educated to know that a bullet( or in this case, buckshots) was travelling really fast and hits me, I might want to do what I can to avoid being hit by it, even if it means I have to learn to use it properly.

  7. I’m pretty sure this topic is fairly dead but to future readers. Please know that wall power is AC so you CANT exactly reverse polarize it. There isn’t any difference between a cross over cable and a regular extension cable. The primary idiot stunt here would be connecting a generator to your mains power without protection.

    I’m 100% sure this was an April Fools joke but I think some people are taking it a bit seriously.. Pretty funny lets make an extension cord out of an extension cord hack.

  8. On the whole backfeeding the grid thing… Doesn’t anyone think that the current draw from all of your neighbors houses electrical equipment would be enough to pop the 15 amp circuit breaker that is on most residential generators? I know that during a blackout I don’t go switch off all of my high load devices so my “crazy” neighbor with a generator can run his stuff without disconnecting his mains breaker…

  9. so hey i just tried it but it didnt work?

    my fusebox just exploded and as for the generator i think it overheated or something ill try it later but anyway have yuo guys tried this yet?

  10. You guys are retarded.

    A mains crossover is a legitimate tool. You simply click off your root breaker (That’s the one between your box and the city), plug the crossover in to that circuit and power the generator.

    People are so safety conscious through ignorance these days it makes me sick.

    You can buy them premade. LOOK IT UP!

  11. You guys are retarded.

    A mains crossover is a legitimate tool. You simply click off your root breaker (That’s the one between your box and the city), plug the crossover in to the circuit you need to power and power the generator.

    People are so safety conscious through ignorance these days it makes me sick.

    You can buy them premade. LOOK IT UP!

  12. You will get someone killed with this post. You need to remove it.
    Some idiot will build this and NOT disconnect his/her house from the grid when plugging his/her generator in, thereby back feeding the power company wires and killing an unsuspecting electric company lineman. Remove it now. It’s not censorship, it just responsible and respectful of human life.

  13. Although I think it’s absolutely senseless to say it here, but don’t you think, that ANYBODY that gets on THIS site and even understands what the article means, will surely realise what’s going to happen? You don’t? I think so.
    The thing just is: Nobody with no interest in hacks/electronical stuff etc would have this as their Homepage in firefox etc, that makes no sense.

    The ones who get killed becaused they were so damn stupid (TWO times there is written that is is just an aprils-fools-day-joke) really desire another Darwin Award!

  14. April fools joke aside, mains crossover cables do exist commercially and they’re exactly the same as the one shown here. The ones I saw were in Asia and were supplied with bi-directional 120V/240V step-up/step-down transformers that had a female socket on each side. They’re pretty dangerous of course, you gotta remember to not accidentally touch the plug when the other end is still plugged in…it hurts! :)

  15. cool! can you do this with 220? I’d love to be able to run my dryer and stove too!

    (just kidding, and next time give instructions that will cause it to be both harmless and ineffective… something like “cut off both ends, don’t worry about stripping back the wires/use two female ends)

  16. I made one of these when I was about 10 years old… my dad still uses it because his house is split into two apartments with different electrical service coming into them, the upstairs has been disconnected for years now, and rather than rewire the circuit breakers, I just made a patch cord.

  17. the only part of this “hack” that didn’t disgust me was when it said to read the warning labels on the extension cords as if you won’t be immediately breaking most of them.

    other than that, as hundreds of people have already said, don’t even post this kind of stuff.

    Some idiot who thinks he knows what he’s doing but doesn’t is going to try this and kill himself or a linesman.

  18. All these electrical engineers, electricians, linesmen that are up in arms about this.

    Don’t you guys test stuff before you grab hold of it?

    I know i do.

    “This bit of copper could feasibly be connected to something that might have some sparks going down it. I think i might put my multimeter on there before i put my hands on there… Oh, look, it’s live. I don’t think i will put my hands on there after all.”


    Test before touch.

    hell, they’ve even got them little pen-like things that light up when there’s a voltage nearby. you don’t even need to get your meter out.

    Stop bitching.

  19. Because it was posted on April fools day it muddied it even more. Things that could have serious consequences should have been posted at a more serious time. That’s what the voices said!

  20. guess i shouldn’t explain the one i have with 4 wires used to power the home in case of an outage with 110 and 220V.

    buncha morons.
    Guess all you folks need to picket gas stations .. ever see how dangerous that stuff is?

  21. What? This is totally safe, I use mine all the time when the power goes out. Just remember to turn off the main breaker. Yes they actually work and I don’t see how they would be dangerous.

  22. A lineman working for the electric company told me that this is exactly why they short “dead” lines to ground when working on them. During electrical outages, some people electrify their house WITHOUT turning off the main circuit breakers, thereby electifying the power lines as well.

    The practice of powering your house with a sufficiently powerful generator is fine, as long as you FIRST disconnect your house from the electric grid, via your main circuit breakers or fuses.

  23. People, if you are on this site to start with, one would hope you have SOME common sense when it comes to working with voltage systems whether they be high tension or low tension, they still use the same respect and caution. Most of the posts I’ve read on this thread are by people who don’t understand the principle of electrical safety. This hack, although an April Fool’s joke, really does work when proper precautions are taken. Please do your homework before posting….

  24. Woah, this article was before my time following HAD and I have to vote for removing it. I think it’s in poor taste, mostly considering the average age of the reader here as evident by the few comments I skimmed. People ignore warnings; that’s a given. The less people that get an idea to do this for real, the less accidents there are from people messing up.

    That said, I do own such a DIY cable, though for 220V operation. It is a valuable tool, but like most valuable tool, can be misused in the wrong hands and someone gets hurt. I installed a secondary main breaker in the distribution panel to make it easier to disconnect; the original main breaker was next to the meter 3 floors and 300 feet away. And I keep a warning taped to the panel to make sure switches are flipped in the right order.

    Also, did anyone mention you have to turn off all your 220V breakers if you are only powering one phase?

  25. One more thought – has anyone thought of using a couple of solid state relays (example would be a Magnecraft W6110DTX-1,10 amp capacity) in conjunction with a PIC or other mcp to disconnect or monitor as a safety op to automatically reroute power back to mains when they come on line? Just another cool idea for a hack…….

  26. I know the ATS would be the easy way to go, but hackers never go the easy way to achieve something spectacular. The idea I had was to incorporate the principle of an ATS and perhaps add a few extra features (based on open-ended code of course) like a bluetooth or Bee to send info status of the mains, whether on line or dead, generator output status, relay status, etc to another device (iPhone perhaps?) for remote monitoring and notification so you don’t have to run over and check every couple of hours. This could also tie in with some of the other hacks like the power consumption sender or other similar ideas so you would only need one mpc with a minimum of code add-ons.

  27. The only pratical way to do it is to instal a proper manual transfer switch for the mech contacts and go to town customizing it all you want. Way safer, as it would make it physically imposible to backfeed the grid, and they are cheaper then ATSs.

    Things like solid state relays are a horrible idea because of the high on resistance.

  28. Although the Solid Satae Relays do have a higher impedance, This hack would also possibly enable the user to remotely start and shut down their generator as well as monitor fuel level from a central location if some type of UPS were in place to continue to provide startup/relay switching. From experience I know that sometimes the breaker panel is not always easily accessed. I am currently working on this project, but unfortunately not bless with much working capital. If someone else were able to, it would be great to see it in real life application!

  29. There’s no ‘although’ for Solid state relays; they are a horrible idea for house mains level current no matter what.

    Also, using a UPS for control power is more complexity and points of failure. They way a simple ATS works is when the power cuts out, a relay drops (de-energizes) and completes the generators electric start circuit. The generator comes on-line, and the ATS uses generator power to actuate the mechanical transfer mechanism.

  30. You Guys seriously need FI switches…

    did that too, to power a room which seemed to be not connected to the power grid, turned out the plu i used was connected -> had to reset fuses

  31. What a bunch of sissies. This is (almost) exactly how I connect my 15KW generator to my house when the power goes out. If you have, and use, half a brain, there’s ~0 chance of any problem. Granted, there are none of the safety stops of the fancy schmancy hook-ups, but if you follow a simple sequential hookup instruction set, there’s no problem!


  32. This actually works.
    1. Shut off the main coming into the house.
    2. Shut off all individual breakers minus the one you want to use.
    3. Plug one end of the suicide cable into the wall outlet.
    4. Plug the other end of the cable to the generator outside.
    All plugs on that circuit is live and can be used.
    1. Unplug the cable from generator.
    2. Unplug the cable from the outside outlet.
    3. Turn on all breakers.
    4. Turn on main breaker to the house.

    It is safe if you respect the power and follow the steps. Driving a car is dangerous if you don’t respect it and follow directions.

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