Building an appliance with two plugs to get double the voltage?

Question

I just had a silly discussion with someone about voltages. In Europe the usual voltage is 220 V while in some other places it's 110 V.

So we were discussing how to use European devices abroad and my friend asked, do you think one could just add another plug to the device to get 220 volts from two 110 volt sockets?

While it seems to be an awesome idea it most likely does not work because otherwise everybody would be doing it.

So we started trying to figure out why it cannot work. While we both have no clue, I suggested that the 110 volts means 110 volts in total for the entire house. I wanted to finish this argument by arguing that if you plug in a toaster that uses 60 of the 110 volts then there is only 50 left.

Except I know this is wrong because no device "uses up" part of the voltage.

So my question is:

Please could someone explain to me in detail why (if) it is not possible to use two plugs to get double the voltage?

Or else, if it is possible, how it works?

Edit

Just in response to some of the answers: We have absolutely no intention whatsoever to actually build anything at all. This is of purely theoretical interest to us and we hope that we learn something about electricity in the process. Thank you for your concern.

Answer 1

if you plug in a toaster that uses 60 of the 110 volts then there is only 50 left.

No, the devices are wired in parallel, which means all devices in a home share the same voltage.

Things are not wired in series like this:

110 V ---------HiFi--------Fridge-----.
                                      |
neutral-------------------------------'

which might mean the HiFi gets 85V and the Fridge gets 25V and neither works because each needs 110V to work.

But are wired in parallel like this:

 110 V   ----------+--------------+
                   |              |
 neutral -------+--------------+  |
                |  |           |  |
                |  |           |  |
                HiFi          Fridge

It may help to think of the usual water analogy. If you have a very large tall tank of water, the pressure at the bottom only depends on the height of water in the tank, nothing else. It doesn't matter how many pipes are connected at the bottom of the tank, the pressure in each pipe is the same. You can't double the pressure by connecting pipes together creatively.

You can double the flow obviously, if one pipe can deliver n gallons a minute, two pipes (the same size) can deliver 2xn gallons a minute. But flow is like electric-current (amps) not like electric-potential (volts).

Your house does have a limit on the total current that can be supplied. This is because wires to your home would get hot if they carried more than their rated current. It is a bad thing when wires get hot, melt or set fire to the surrounding buildings and to the people in them.

So if your house has a 200A supply and charging your Prius takes 100A that only leaves 100A for the rest of your appliances. But that is current, not voltage.

why (if) it is not possible to use two plugs to get double the voltage?

Because you'd just end up doubling the wires (to no effect) or shorting 100V to neutral and blowing a fuse / tripping a circuit breaker.

You can do this with multiple batteries. For example, connecting two 1.5A AA batteries in series (one after another) does create 3V. But you can't create 3V from a single 1.5V battery just by creative wiring. Your household 110V AC supply is more like a single battery with lots of items connected by wires.

The USA does use a "split-phase" supply to houses (think two-batteries) which means you can create 240V by making use of both phases. There are rules about how you do this and anyone without a basic grasp of the principles of electricity should not mess around with this.

Answer 2

First an important note: This is mucking around with potentially lethal circuits and in no way should anything that might be suggested as a result of this answer this be attempted by other than a properly licensed electrician. In particular the OP does not have enough knowledge to do this without severe risk to life and limb. Few of us here are licensed electricians. See the DIY SE if you want such advice on what is safe and/or acceptable to actually do.

It's possible, albeit unlikely, that this will work in some cases in North America.

First, if the outlets are connected to the same circuit, or to another circuit on the same phase it will not work. To get the two to 'add' you would be shorting them out. It would work if you isolated one with a (big heavy expensive) 120:120 transformer. The transformer could be about 1/2 the size of a 120:240 transformer because it is effectively an autotransformer.

Now, the limited cases where it might work: North American residential power is typically center-tapped 240V already, with each phase routed to different receptacles throughout the house and 240V routed only to a few high consumption appliances (stove, dryer, air conditioner compressor unit). In some cases outlets in the same room will be connected to different phases so there will be 240V between them. (At one time it was even kosher to split receptacles (top and bottom) but that is no longer sanctioned - presumably because GFI outlets are mandated in kitchens, just where you might run into such a situation). Older "split receptacle" installations certainly exist and are grandfathered.

In a large apartment building its more complex, with 120V as one phase of three, and the sum of any two 120V phases (\$208V=120\cdot 2 \cdot \sin(\pi/3))\$for major appliances).

So the 240V/60Hz already exists in most houses (not necessarily apartments). Whether it is kosher to rewire this to power some random foreign appliance is then an electrical code issue, which the good folks at DIY would be be able to advise you on. 240V outlets are allowed and are typically in locations reserved for major appliances, They are not the same as any foreign domestic or North American industrial 240V outlet - usually bigger than the former. See for example, this answer that touches on some of the subtleties.

Wiring diagram from here

Answer 3

By asking your questions its obvious that you have no electrical background, so I try to answer with an analogy.

You can to a certain extent think about electricity like a water piping system where voltage is the pressure, current the amount of water flowing through the pipe and the diameter of the pipe (which is limiting the amount of water going through it per second) as the resistance.

If you split the pipe to 2 separate paths, the pressure of the water in each of the paths is still the same as in the pipe before i.e. your voltage is still the same, no mater how many plugs you add.

But what you did is you increased the pipe area (you doubled it) and therefore you can get now more water per time out of the pipe i.e. you decreased the resistance and therefore allowed more current to flow by adding the second plug (in the 'electric' world the current limiting factor is usually not the wire but the device itself, though your wire has to be big enough to carry the current needed).

Answer 4

You would need to find two outlets on two different circuits with one circuit on one phase and the other circuit on the second phase.

On a typical electrical panel the breakers alternate between the two phases as you move down the panel, so you can find the two different circuits e.g. Living Room and Dining Room.

So if you choose these two outlets, they will each have a common ground and common neutral at the panel so there will be ~220 potential between the two hot/live wires. Your two plugs would go into each of the two outlets. You will probably need an extension cord to get to the second outlet!

This is how 220v appliance work in the US. For example, a 220v clothes dryer has a 2-pole breaker bringing in two hots to the dryer, each from a different phase.

Answer 5

At least in North America, homes get 240V from the power utility. But it is "divided in half" and each half (120V) is wired to lighting and outlet circuits for plugging in appliances. High-power electrical devices (heaters, etc.) use the two "phases" of the 240V directly. So 240 can be found in circuits for high-power devices.

But for European appliances, they typically want a "hot" leg of 240V, and the other end is "neutral" which is ground at some point. There is no way to safely get that directly from a typical North American power wiring scheme.

That is why people use transformers to convert between 120 and 240V (and vice-versa).

You theoretically COULD make a gadget with TWO long power cords and go searching through the house to find an outlet circuit on the OTHER "phase" and you would have 240V, but BOTH sides would be "hot" and that would be rather dangerous unless you REALLY REALLY knew what you were doing. This is a theoretical illustration and is ABSOLUTELY NOT RECOMMENDED in actual practice.

Answer 6

To be blunt, no, you don't use two plugs. The other answers do describe scenarios where you could, however I you understand enough to get the two normally available phases of line voltage in an average US home, you will instead configure an outlet properly.

There are several types of NEMA outlets, the below illustration shows typical offerings for 120 and 240 VAC.

If a device only needs 240 VAC, the return/white/neutral conductor is not used at all; all current is between the two hot lines, typically red and black. If a device wants to use 240 VAC and 120 VAC, it will need a neutral conductor. The image might be misleading; I have observed a NEMA 10-50 outlet commonly used for dryers and electric ovens/stoves.

If three phase power is present, there can be a blue wire. Any connection between two colors is 240 VAC; additionally any connection from a color wire to white is 120 VAC. As an aside: Beware of white wires with black or red tape at the end, they will be hot.

Answer 7

Seeing as how you are merely going through a thought exercise, then like said, it is doable to get 220V from the two phases going to different outlets (you just have to locate them).

Grant Thompson did so in this video showing how to make a spot welder with 2 microwave transformers - https://www.youtube.com/watch?feature=player_detailpage&v=hsfgwEUXtTc#t=212

Safe? No. Possible? Yes.

Good thought exercise.