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?

392 thoughts on “How-to: Make a Mains Crossover Cable

  1. This is one of the most dangerous things you could show. Someone will get killed with this. And never try to connect a running generator to the power lines as you show. At a minimum, you’ll burn up the generator, and possibly kill your self. The generator will be out of sync with the power line, and smoke and sparks will happen, and possibly other bad things. Bad idea to show people how to do this….And, yes, I am an electrical engineer……

    Perry Vale

  2. Not as useless as you think.

    During a power cut, you flip your primary breaker (separating your house from the mains) and use one of these cables to connect your generator to all the sockets in your house.

    When your neighbours’ lights come back on, switch off the generator, unplug the cable and flip your breaker back on.

    1. Not as useless as you think.

      During a power cut, you flip your primary breaker (separating your house from the mains) and use one of these cables to connect your generator to all the sockets in your house.

      When your neighbours’ lights come back on, switch off the generator, unplug the cable and flip your breaker back on.
      Brilliant! *Thumbs Up*

  3. This isn’t that bad! Think about it. there is a power outage and you want to supply power to your entire kitchen. Turn off all of the circuit breakers, do this hack, and plug it into your kitchen outlet. BAM! everything on that circuit comes to life!

  4. I agree with the other poster, delete this post. You could be sued if someone kills themselves. There is a hack limit, and when playing with mains power, you’ve crossed it.

    Perry Vale

  5. Well its not crimial, however, there are extreme dangers for doing this.

    You need to ensure that the mains breaker is thrown before using, as this system WILL backfeed power upstream to the power poles. This is a potential hazard for any lineman working on your service.

    A much safer alternative is having a licensed electrician install a secondary panel for your generator.

  6. This should be treated with respect, and don’t connect two circuits with power on them. Don’t plug one end into a circuit with power and leave the other end laying around. This can be used to connect a generator to a house easily, but make sure the main breaker is off just in case the power is restored while the generator is connected. Don’t turn on many appliances because your pulling an entire houses current through a wire meant to supply 2 or 3 heavy appliances at most. Ok, I’m done ranting for today.

  7. I don’t think we needed this post. People that need an step-by-step explanation for this hack shouldn’t use such a thing in the first place.

  8. I hate to say it, but this is a love-hate thing.
    Cheap, effective, and profitable for the undertaker and funeral homes :)(haha, yeah, sorry for the dry humor)

    I’m guilty of using one to flash an old generator, and back-feeding the 220 circuit during an outage, but with codes approved transfer switches only being around $100 for the low end I’m thinking of biting the bullet and installing one.

    Just remember, treat everything proper, and you won’t have any issues.

    And for gods sake don’t lick it…

  9. I bet you guys saying “get rid of this” love having signs that say “Danger Low Head Space” in areas with low ceilings.

  10. I’ve done this (hurricanes, weeks without power) and it can’t be overstressed that making mistakes with something like this can kill you or others.

    Lots of power company employees have been injured / killed due to someone hooking something like this up and leaving all breakers in place. You’re far better off getting a load transfer switch in place before doing this.

    Hack safe.

  11. @Fred

    A few years ago, I’d agree with you 100%.

    However, since then, the reader base of this webpage (and subsequently, the articles) have gone rapidly downhill.

  12. There are actually commercial versions of this, but they all have a cutoff switch which gets installed at your power box. They then can only plug into a plug which to get access to you need to open a breaker disconnecting you from your mains..

    But as shown it is just a problem waiting to happen, and in many areas it is against the electric code and so illegal..

  13. @bencoder even if this is supposed to be an april fools joke, it is not only a very bad one – it is a deadly one.

    Even people who don’t need a HOWTO to build this cable shouldn’t do it because it is just to dangerous.

  14. This is an amazingly fucking stupid thing to do, and in some places, it’s a crime. These things are colloquially known as suicide cables for a good reason. As others have noted, rigs like this have injured or killed utility workers when the main breaker was not shut off properly.

    When you get a generator for backup, get a proper load transfer switch with it.

  15. Something not covered in the writeup is, this should not be used to support any major amperage/wattage because it bypasses the safeties (fuses) of the house by placing the fuses at extreme ends of the power conduit. Sure, there may be a fuse on the generator, but you’re using a heavy-gauge “crossover” cable to feed into “minor gauge” house wiring.

    Most house wiring won’t be heavier than 14ga, and to be putting (potentially) all of the house’s circuitry through a single 14ga wire to its power source, is very unwise. Even if it doesn’t cause a fire now, the wire could get hot enough to melt through the shielding and cause a problem down the road.

  16. This is very useful.

    Why?

    If you make a cable like this and have a power outage, one can effectively power their house safely by using the mains crossover and removing their mains fuse, therefore preventing backfeed from the power company and keeping yourself and your property safe.

    But, the proper safety requirements must be held. If you don’t know already how to do this, you probably shouldn’t be doing it. This is useful information in case of a disaster, but with electrical currents, always assume something is live and deadly. Don’t chance it.

    Also to all of the people BAWWWING about how this should be taken down: STFU

  17. I have one of these – only mine plugs into a 220V, 40A outlet. Electricity coming out of your outlets isn’t magic – suck it up, pansies!

  18. G’pa died this way. He was a line man working after a hurricane and someone left their breakers on and back fed a generator. he restored power and BOOM! toasted. It’s not to be done. period. If you need to run your entire kitchen then get a heavy duty power strip and some extensions to run only the bare essentials.

  19. People who need a guide on how to this, or why it works shouldnt be doing it.

    Seemed pretty obvious how to so this. Similar concept to something i saw a few years back, Involved using what ammouted to a UPS, and a cord similar to the one posted above to remove a mains powered device from where it is plugged in to somewhere else (see steal it) without turning it off.

  20. Hmmm….needs more sarcasm in the build process for folks to realize it’s a joke.

    Surely, if you are dumb enough to do this without realizing the consequences, you should be surrounded with bubble packing tape for our safety and yours.

  21. “If you do not know why you should not attempt this, you should not attempt this.” I love this disclaimer. If you know why you shouldn’t do this hack, you won’t do it. If you don’t know why not to, the disclaimer says you shouldn’t!

    Happy Apr. 1, everyone! Stay safe.

    Jonathan.

  22. First off, it’s tagged April Fools…they’re obviously joking.

    Second, this does work and can be done safely if you’re not an idiot. All you have to do is use your breakers to isolate the circuit you are powering. I have a cable similar to this with 220 volt plugs instead that we use when the power goes out. You just have to turn off the main so you don’t backfeed the lines and kill a linesman.

    I wonder how many of the people screaming bloody murder are also members of the Arduino crowd. ZOMG, it has more than 5 volts?! Kill it with fire!

  23. HAHA! awesome! I love april fools! its amazing how many people get worked up about it!
    Reminds me of the war of the worlds radio broadcast. lol

  24. Oh so serious. It’s like we have a collection of product liability lawyer wannabes on here.
    @TOM – looks like you’re right. Quality of the readershipp has plummeted. Now it’s a bunch of namby-pamby serious sams pointing out the dangers of…God forbid…a HACK.

    Yep, there’s always a few idiots who’ll try it, and there’s always a few product liability lawyers who’ll “try” it as well. But in the end, if you’re this stupid and missed the date on the calendar, well, maybe you should check in your subscription and go back to engadget.

  25. This is illegal and for good reason. Not only could you destroy your generator, kill yourself and loved ones, burn down your house, but you could also kill a lineman working on the downed lines.

    I’m all for free speech, and it’s the Author/Editor/Parent Company’s right to post this; but this is something that I would highly suggest removing from the site.

  26. If this is an April Fools Joke; very bad taste.

    If this is a serious post; you must be absolutely mad.

    Any half serious EE will / is telling you this is a seriously bad idea to post this. Anyone who is capable of making one of these already knows how to make one (and how to use it safely), and anyone who doesn’t definitely shouldn’t make one.

    This ‘hack’ will and does regularly kill linesmen, and very much has to potential to kill noobs who try it.

    It is criminal for you to be advocating such a half arsed bodge on this site.

    I usually like reading hackaday. Won’t be coming back if this is the absolute level around here now.

  27. This is a really irresponsible thing to put up on the site, it’s blatantly dangerous to not only yourself and your property, but also to people outside your home.

    First–this is an obvious hack to anyone who understands mains power

    Second–anyone who could NOT figure this out on their own is probably too stupid to safely use it and will end up killing themselves or someone working on the line outside.

    Putting aside the obvious fact that you’re back-feeding only one phase–meaning 1/2 of your single phase circuits and all of your two phase circuits will still be powerless–you should realize that these outlets are typically 15A, meaning about 1500-1800W max, even if they are 20A that’s only 2000-2400W.

    So at that level why not just run some cords around the house? Chances are good your generator creates more then 2000W of power anyway unless it’s really tiny, so to prevent fires, tripped breakers, etc, you’ll end up running multiple cords anyway.

  28. BTW, I agree–if this is an April Fool’s joke it’s in REALLY poor taste… sort of like waking up your wife to tell her the baby is dead…

  29. I’ve actually made and _used_ one of these! I was moving out of my apartment, and the utility company shut off my power prematurely. I just whipped one of these together out of an old extension cord, and “borrowed” power from a hallway outlet for a short while. Just make sure that you don’t try to draw too many amps. IE, unplug your fridge if you have more than one other light on.

  30. I think even a child could tell you that this is pretty dangerous, you don’t really need a “how to” to connect two mains plugs onto a bit of flex.

    Saying this though I did something similar a few winters back when I was without power for a week after a JCB chomped through the main feeder for the estate I live in. I managed it safely and didn’t manage to injure myself.

    If you are stupid enough to kill/injure yourself maybe you are just proving to the rest of civilisation that your DNA isn’t required anymore….

  31. @Ricardo,

    It’s not just yourself that you put on the line. If some numbnuts connects this without isolating the Mains feed you will backfeed the main, possibly injuring or killing the poor sap who has come out to fix your power.

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