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Thread: 220v from 2 x 110v plugs

  1. Ok, a capacitor will do nothing. You shouldn't even be thinking about these modifications if you think it will. 50 milliamps is all it takes to kill a person stone dead. Don't take chances.

    Do what's right and safe. Take a pass, or use a UL Listed device as mentioned above (if it even has a listing).

  2. Quote Originally Posted by Tom Veatch View Post
    Really no different than sticking a knife into the hot side of any live receptacle.

    Am I understanding it correctly?
    Yes. Male prongs with 120V on them.

  3. #33
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    I'd like to respond generically to a bunch of the posts in this thread.

    • I don't think it's a good idea to tie (2) 120v circuits together to make a 240v circuit unless you know what you're doing. The gizmo posted sort of makes this foolproof.
    • There is NO NEC PROHIBITION to doing this. The NEC (and locally adopted modifications to the NEC) apply to the wiring in the building - NOT what you plug into the receptacles.
    • It is true that, in extreme circumstances, one could create a potential where a single hot leg transmitted current through a load to energize a pin on an opposing plug. I'd say that likelyhood is pretty slim. The gizmo posted would prevent this from happening. You could also build a device to do this.
    I would still go back to my final advice and have an electrician install a circiut. If, as suggested, you can get the building owner to agree to installing a subpanel in your workspace, I'd pay to have that done.

    To all of the posters who have said that tying (2) 120v circuits together can not be done - shame on you. Your statements are electrically wrong. Still, doing it "SAFELY" means understanding what's going on with the wiring, which is a big IF and not something I would trust a typical non-electrician/homeowner to be able to do safely. That does not mean that tying the 2 circuits together safely can't be done.

    Please note that I'm not advocating tying (2) 120v circuits together to create a 240v circuit.

    As I posted earlier, the best route is an electrician and installing a circuit or subpanel in the workshop.

  4. #34
    Quote Originally Posted by Tom Veatch View Post
    Jason, check me on this, please. I'm trying to be sure I understand why it's dangerous.

    You've got two power cords going to the load, each plugged into separate 120v sockets. One power cord gets unplugged while the other is still plugged into a live circuit. Is that the scenario we're looking at?

    If so, that's the same situation as a single power cord with a plug on each end where one end is plugged in and the other just laying out on the floor. In that case, the "hot" prong of the unplugged end is directly connected to the live "hot" and exposed for all the world to see and touch. Really no different than sticking a knife into the hot side of any live receptacle.

    Am I understanding it correctly?
    Tom, exactly right. That's precisely the danger of just throwin together an extension cord as has been advocated. You need to KNOW that no metal can be touched that will hold a charge. It's terribly improper to suggest that such an idea is safe.
    Jason Beam
    Sacramento, CA

    beamerweb.com

  5. #35
    Are you sure you need 220V, even? Most motors wired for 220V can be changed to 120V easily. Perhaps you have heavy gauge wires and short runs to the breaker box, in which case, the 220V might not gain you anything.

  6. Geez, I can't believe how many "the sky is falling" postings there are on this topic. It would seem that those people screaming the loudest don't really understand the topic. Shame. Instead of throwing your arms up into the air and screaming, offer some advise. (I guess Rob's last posting kind of stated what I mean, but I didn't see it until I was nearly finished.)

    • If the building has a 120/208 3-phase supply, it will make no difference whether he hires an electrician or not, he is still going to only get 208 volts from any receptacle, so this is completely off topic.
    • If one circuit breaker trips, the tool just shuts off. It doesn't get half the power, and it doesn't pose any threat to the operator or circuit.
    • The only danger to doing this is a backfed voltage, and even that is only an issue if someone unplugs the cord.
    • Before there is a problem with backfed voltage, three things need to happen. If one of those three items is missing, then there will be no problem.


    1. A tool must be plugged into the 240 V receptacle. No tool; no backfeed.
    2. The tool must have a non-switched load, or the switch left in the On position. Most tools with magnetic starters that do not have low voltage controls will automatically cut out, and there will be no potential for a backfed voltage. Most retail grade woodworking tools use mechanically driven magnetic starters, and when they are off, there is no path for a backfeed. Very few of these tools will have the low voltage controls with a transformer, and even still, the transformer is a high impedance path.
    3. And here's the biggie...someone needs to unplug one of the power cords from the wall and touch the exposed prong. If you don't unplug it, then there cannot be a problem.
    Obviously this isn't something you want to do willy-nilly, nor should it be considered a long-term solution, but it will not blow up the shop either. Under other circumstances, I would probably be cautioning you more, but that has been done quite enough already.

    Oh, one thing that no one has mentioned is that this concept will not work if the outlets are GFCI protected. The GFI will trip because no current will be recorded in the two neutrals.

  7. #37
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    If I may, can I pose this question? Can a 20A, 110V outlet be converted to 220V? That is provided that it is the only outlet on that circuit, and that there is an empty slot next to the breaker at the breaker box. Will the existing 120V wiring be too small for the 220V power?

    Ed

  8. #38
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    Quote Originally Posted by Ed Bamba View Post
    If I may, can I pose this question? Can a 20A, 110V outlet be converted to 220V? That is provided that it is the only outlet on that circuit, and that there is an empty slot next to the breaker at the breaker box. Will the existing 120V wiring be too small for the 220V power?

    Ed
    Ed,

    Assuming (2) things:
    • The circuit was wired with #12 and,
    • The empty slot means you can put in a fullisize, 2-pole breaker (vs. the halfsize breakers), then

    Yes - you can convert the circuit from 120v to 240v by replacing the single pole breaker with a 2-pole breaker. Reemmebr to reidentify the white/neutral conductor with some black tape or permanent marker to signify that it's a "hot" conductor.

  9. #39
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    Quote Originally Posted by Duncan Horner View Post
    Chris: Yet you thought it was a bad idea in your first reply?

    Same setup as propositioned by OP, and just as dangerous.

    Good point about breaker access however, I'm pretty sure the code *does* say something about the only disconnects being located in an inaccessible location.
    Yes, I still think it is a bad idea. All I was responding to was the multi-wiring...nothing else.
    Wood: a fickle medium....

    Did you know SMC is user supported? Please help.

  10. #40
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    Quote Originally Posted by Ed Bamba View Post
    ... That is provided that it is the only outlet on that circuit, ...
    That implies that maybe only one outlet is allowed on a 240v circuit. That is not the case. You can have multiple outlets on a 240v branch circuit just like you can have multiple outlets on a 120v branch circuit.
    Tom Veatch
    Wichita, KS
    USA

  11. #41
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    Tom, I think he meant to make sure that you don't accidentally connect other devices on the circuit to 240V.

    Regards, Rod.

  12. #42
    Quote Originally Posted by Tom Veatch View Post
    If it were DC, the capacitor would stop the flow once it were charged up, but a capacitor will pass AC current. The smaller the capacitance, the higher the effective resistance at a given cycles per second but you'll still get some current flow for any finite value of capacitance.

    I meant a diode... not a capacitor... a capacitor would probably make the system more lethal as it would built up a charge... that's what I get for reading late at night. Isn't a diode installed in a circuit to limit the flow of power to a single direction?

  13. #43
    Quote Originally Posted by Tom Veatch View Post
    Jason, check me on this, please. I'm trying to be sure I understand why it's dangerous.

    You've got two power cords going to the load, each plugged into separate 120v sockets. One power cord gets unplugged while the other is still plugged into a live circuit. Is that the scenario we're looking at?

    If so, that's the same situation as a single power cord with a plug on each end where one end is plugged in and the other just laying out on the floor. In that case, the "hot" prong of the unplugged end is directly connected to the live "hot" and exposed for all the world to see and touch. Really no different than sticking a knife into the hot side of any live receptacle.

    Am I understanding it correctly?
    In one scenario you have a female end of the plug that is hot, and you would actively have to "stick a knife in it" or something else to ground the charge.

    In the second scenario you have an exposed male end of the plug, which by all convention and tradition, if it is exposed, should not have any charge in it... and could easily be touched.

  14. #44
    Well after much heated discussion, while potentially feasible, it doesnt seem like the best idea. I'll talk to the landlord, and see about getting a 240v plug installed, even if it is at my cost.

  15. Quote Originally Posted by Todd Pretty View Post
    I meant a diode... not a capacitor... a capacitor would probably make the system more lethal as it would built up a charge... that's what I get for reading late at night. Isn't a diode installed in a circuit to limit the flow of power to a single direction?
    AC current means Alternating Current. Meaning half the time it flows one way, half the other. A diode would only stop it half the time, and would stop AC motors from working at all. An even worse idea than the capacitors lol

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