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Technology, current at the time of US electrification, locked the US into 110, then 120 volt outlets. Europe's electrification came later, and proceeded in response to advanced technology. The US was too deep into the 110/120 volt infrastructure to upgrade. The US has remained in this situation ever since.

House voltage was first determined by Thomas Edison who set it for optimal performance of his equipment.

Additional Information:

The United States distribution system actually provides a 240 volt residential service in the form of two 120 volt conductors and a neutral conductor. You can see this if you look inside your breaker panel. When a load is applied from either 120 volt conductor to the neutral (as is the case for typical receptacles, lights, and so forth) it is using 120 volts.

However, when a load is applied from one 120 volt conductor to the other, without using the neutral, the voltage being used is the sum of both 120 volt conductors (240 volts). This is the case for many water heaters, air conditioners, electric furnaces, clothes dryers, and so forth.

So equipment that is connected to strictly 240 volts is connected with only a two wire cable plus a safety ground wire. (For example 240 volt base board heaters use this.) The only time a cable with three wires plus safety ground is used is if 120/240 volts is needed in the equipment. (For example kitchen ranges or washing machines which have time clocks or programmers that require only a 120 volt feed.)

For systems outside the US, receptacles are 240 volts. Lower voltages tend to be safer, which is why in the US, you are receiving 240 volts at the home box and 120 at receptacles, instead of the thousands of volts generated by the power plant.

Power is transmitted over High Voltage cables - usually above 10K Volts. The power is then stepped down before it reaches consumers. Outlet power in the US is 120 volts, increased from 110 volts sometime around 1950.

The US system theoretically could be made as good or better than the European system with no infrastructure change, except appliances and consumer structuresthemselves (collectively costing home owners billions). US houses get 240 volts at the panel. If wall outlets all were fed with 240V you'd have the lower current and higher power advantage of the European system and it would be safer too, since each "hot" would still be only 120V from ground (not 240V) which keeps the reduced shock hazard advantage. Of course it is still possible to touch the two hots.

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The origin of the 120 volt standard dates back to the feud between George Westinghouse and Thomas Edison. The first public electricity utilities were set up by Edison, whose concept was that there would be a power station (Coal fired) at the end of every street, supplying low voltage DC. Westinghouse came up with the idea of using AC, which can be transmitted over long distances from a small number of giant power stations. Edison worked to get the concept banned to protect his system by claiming that it would lead to the use of dangerously high voltages.

The result of this public debate was that the US opted for the low voltage, but using AC as Westinghouse recommended.

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โˆ™ 2013-08-29 16:27:42
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Q: Why does the US run at 120V when some of the world runs at 240V?
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Related Questions

What is a Single pole electric service?

Do you mean Single Phase? This is what supplies American homes and some commercial buildings. It is 120V/240V.


WIll sump motor blow if I connect 240V?

It may not blow, but it will turn twice as fast and burn out very quickly. It is meant for 110 only. Check the sump pump. Some of them can be wired either 120v or 240v. If yours is like that, just wire the motor for 240v and plug it in.


Can you use a 120v cord that will fit a 240v socket the appliance is 240 and the cord is thick?

120v and 240v cords usually have different end configurations and will not plug into the different recepticles. However, if you changed the plug end, and the cord has the proper size rating, then yes, you could use the same cord. But, it also depends on the cord too. Most 120v cords only have three wires in them. One "hot one "neutral" and one "ground" wire. A 240v cord would have FOUR wires, two "hot" wires, one neutral wire, and one ground wire. Therefore, if you changed the voltage from 120v to 240 using a 3 wire cord, you'd not have a ground wire and that could be VERY dangerous. Note that occasionally a 240v device (e.g. some motors) will only need three wires (red,black,green, no neutral) and can be wired with a 120v cord if the cord is rated for 240v.


What can you power on a 2000 watt generator?

It depends on what voltage outputs you have on the generator. Some generators have 120V only. Some have a combination of 120V and 240V. Watts = Amps x volts. If the generator has only 120V output then you can pull, Watts/volts = 16.6 amps from the machine. If you have 240V capacity then you can pull, Watts/volts = 8.3 amps from the machine. To put it into perspective a toaster draws about 1500 watts. Check your appliances and check out what they draw. Appliances are usually rated either in amps or watts. My personal generator is 6000 watts and I can carry part of the house load on it.


What happens if you plug a 240V electrical appliance into a 120V circuit?

At best, nothing will happen; the appliances won't run. At worst, the appliance will try to run on the lower voltage, fail to do so, and damage some of the mechanical parts. This is one of the reasons why a 240V appliance has a different plug than a 110V item.


How can you convert a 240V clothes dryer to 120V?

You really cant do it because a 220 has a heating element in it to dry the clothes unlike gas that uses fire to dry the clothes and the 120 is to turn the drum.Your drier will keep poppin breakers which isn't good at all.Outlets and Power(110V outlets and 120V outlets are practically the same for this discussion. I will refer to them as 120V. Same with 220V/240V outlets.) By 110V outlet I'm assuming you mean a standard US 120V 15A outlet.This outlet can provide a maximum of 15A at 120V. This means the outlet can provide 1,800W of power. ( Volts x Amps = Watts ) This is the maximum amount of power this outlet can provide, no more. Also, this is assuming nothing else is drawing power off the circuit this outlet is on. If you try to pull 1800W from an outlet and plug anything else into this circuit, the breaker will blow.Your dryer is designed to run off a 30A 240V circuit. Let's say, for argument, it draws 24A at 240V. This means your appliance requires 5,760W of power to run correctly. This is 3.2 times the absolute maximum amount of power your 120V outlet can provide. There is no way you can run this appliance off this outlet. You have a larger problem here than the voltage difference.You can't, you need both a and b phases. You need to install an 240v receptacle.And don't upgrade to 240V by using the same wires!! Some complete idiots will try this and burn the neighborhood down.


How can you convert a 3-prong 240V appliance outlet to 120V without rewiring and replacing the outlet?

For USA, Canada and countries running a 60 Hz supply service.1) An outlet for 240V is totally different from a regular 120V outlet. 2) The wiring for 240V is also much heavier than for 120V.3) The double pole circuit breaker necessary for 240V is different to the single pole breaker used for 120V.4) Anyway it is not clear why you would want to try to change a 240V outlet to a 120V type?5) If you could log in and add some more details below here so we knew your reasoning for wanting this change to take place, someone may be able to assist you much further.The reason why I need to do this is because there is only one 3-prong 240V outlet in the water heater closet feeding an inline water heater and I want to install an instant hot water recycling system which runs on 120v I so need the extra power outlet.If you want to keep the existing 240V water heater then you cannot add another outlet to the circuit, not even a 240V one, let alone a 120V one!The wiring and its circuit breaker is only rated to carry the current for one water heater and nothing else. If you add another appliance to the circuit you risk causing a house fire: the breaker may buzz but not trip so that the wiring gets hotter and hotter until something catches on fire!So, if you are planning to buy a new hot water recycling system it surely deserves to be installed safely and correctly?So why not, for your instant hot water recycling system, have a licensed electrician install a separate 120V circuit with the correct breaker, the correct-sized cable and the correct outlet near to the existing 240V outlet?As always, if you are in doubt about what to do, the best advice anyone should give you is to call a licensed electrician to advise what work is needed.Before you do any work yourself,on electrical circuits, equipment or appliances,always use a test meter to ensure the circuit is, in fact, de-energized.IF YOU ARE NOT ALREADY SURE YOU CAN DO THIS JOBSAFELY AND COMPETENTLYREFER THIS WORK TO QUALIFIED PROFESSIONALS.


Can you use 120V appliances on a 240V outlet?

Some appliances may work, but I imagine most would either blow a fuse or just burn out. Definately not advised unless you use a transformer. With the right transformer everything should work fine.


Are 120 volt stackable washers and dryers made?

Answer for USA, Canada and countries using similar 60Hz household electricity servicesSome appliances need two power leads, 120V for the washer and a separate 240V for the dryer. Others need only a single 120/240V service. Check what is available at your local electrical goods stores or from online websites.


Why do you have only partial electricity in your home during a local power outage?

Maybe you have a 'brownout', vs. a blackout. Brownouts are the result of undervoltages. i.e. 90v instead of 120v. This can cause lights, etc. to work more dimly than usual, and some appliances may work while others need the actual 120v. Another possibility is that you lost only half of your split single phase service. This would cause all 120v appliances connected to the good 'half' to work normally. The 120v appliances on the other 'half' would not work, and all 240v appliances would not work.


Will a diode work as a light dimmer when switched or added in series to an incandescent 120 volt AC bulb?

Actually, I have seen this in a respected electronics magazine (Elektor) quite some time ago: A diode (selected to be capable to handle the amps, the voltage and the heat from the bulb - if placed inside the lighting fixture) is used to "cut off" one half of the AC sine wave and thus sending pulses of 120V to an incandescent light bulb, simulating a simple dimming device. The proposal was meant to run 240V bulbs at 50% of their brightness but I am pretty certain this concept can be used to run 120V bulbs from 240V power. One other way of connecting 120V bulbs to 240V would be to connect two 120V bulbs OF THE SAME WATTAGE in SERIES, so the two bulbs form their own voltage divider. Not sure what happens if one bulb burns out - I would expect the other one to blow too, as a dying light bulb represents zero Ohms (plasma/arcing) for a few milliseconds before it goes dark forever.


Is it possible to run a computer power supply off of a 240volt utility socket I was told this would reset it as it won't run on 120volt anymore. Is there a risk of shock Do I need a thicker cable?

NO. Don't try it. Some are designed to work on either, some aren't. If it won't work on 120v, it won't work on 240v.


How do you convert a 120V receptacle to a 240V receptacle for a European stereo system that uses 230V if the Stereo has no toggle switch to 110V like some units on the market?

You can't "convert" a 120V receptacle into a 240V receptacle.A proper new 240V branch circuit complete with correctly sized circuit breakers, wiring and socket outlet is required.For more information see the Related Question shown below.As always, if you are in doubt about what to do, the best advice anyone should give you is to call a licensed electrician to advise what work is needed.Before you do any work yourself,on electrical circuits, equipment or appliances,always use a test meter to ensure the circuit is, in fact, de-energized.IF YOU ARE NOT ALREADY SURE YOU CAN DO THIS JOBSAFELY AND COMPETENTLYREFER THIS WORK TO QUALIFIED PROFESSIONALS.


Can you run 220V 50Hz on 120V 60Hz?

If you mean - can you run a 220v device on 120v where the 220v device needs that level of voltage to operate correctly then the answer is no. Even disregarding the frequency difference which some devices aren't affected by, the voltage difference is too great. Some devices these days, such as phone chargers, laptop power supply units etc will run happily on a voltage range from 100v up to 240v (read the label first) but they are the exception. The question is somewhat ambiguous and needs more information.


How do you know if 110v device can be used in 120v outlet?

110V and 120V are essentially the same thing--don't worry about that. 50 Hz vs. 60 Hz is more important, for some devices. North America is 60 Hz; much of the rest of the world is 50 Hz.


Do devices operate on AC or DC?

Some devices operate on AC and others on DC. Generally, anything that uses mains electricity (120V US, 240V UK) is using AC electricity and things that use batteries or are rechargable like cell phones, ipods, personal CD, use DC electricity.


Are 110 volt stackable washers and dryers made?

Answer for USA, Canada and countries using similar 60Hz household electricity servicesPlease note that the standard voltage for 60 Hz electric power services is now 120 volts.Some appliances need two power leads, 120V for the washer and a separate 240V for the dryer. Others need only a single 120/240V service. Check what is available at your local electrical goods stores or from online websites.


Are 115 volt stackable washers and dryers made?

Answer for USA, Canada and countries using similar 60Hz household electricity servicesPlease note that the standard voltage for 60 Hz electric power services is now 120 volts.Some appliances need two power leads, 120V for the washer and a separate 240V for the dryer. Others need only a single 120/240V service. Check what is available at your local electrical goods stores or from online websites.


Can you plug 110 115 or 120 volt appliances into a 220 or 240 volt outlet?

NO! Check the rating on the device and if it says 120V only don't ever dare plug into 240V. Depending on the appliance the results will either be lots of sparks, large flashes or other undesirable side effects.Another engineer's opinionThat answer above is for USA, Canada and other countries which use the 60Hz electrical service standard, for appliances which were designed to run only on that voltage and nothing higher.If this question is asking about using 110V to 120V appliances plugged into sockets elsewhere in the world which use the 50Hz 230 to 240V electrical service standard - such as Europe, Australia and many other countries - then the answer is not necessarily NO.Providing you use the correct type of plug adapter to suit the sockets in each country you visit, if the appliance was designed to run on 110V to 240V services, then the answer is YES.There are many personal electrical and electronic appliances which were designed to run on voltages within a wide range such as 110 to 240 volts! Just a few examples are: electric razors, hair dryers, battery chargers for digital cameras, mp3 players, etc.IMPORTANT SAFETY NOTESuch multi-voltage small appliances should never be used on the 220 to 240 volt outlets in USA or Canada or other countries which use the 60Hz electrical service standard.Such 220 to 240V outlets are intended for use only by large appliances, such as water heaters, clothes washing machines and dryers, cooking ranges, etc. Such 220 to 240V outlets are quite different in size to 110 to 120V outlets anyway and no adapters should ever be used to try to use those kinds of portable small appliances on 220 to 240V 60Hz.It may be illegal to do so in some countries or states because:correct size lower voltage 110 to 120V outlets are available to be used andif one of those small appliances gets a fault, the circuit breakers protecting a 220 to 240V branch circuit probably won't trip to break the current, which could result in enough flames to start a house fire.


What is the voltage on the high leg of a three phase electrical service?

There are two aspects to consider: 1. There are several different standard voltages and connections used by the power company in three phase service. 2. Depends if the voltage is measured phase-to-phase or phase-to-ground/neutral. The three phase-to-phase (A-B, B-C, C-A) voltages should be roughly equal. In typical service, they may be 208V or 240V. The phase-to-neutral voltages are sometimes intentionally different. For example, some 3-phase service has a "high leg" that is 208 volts with respect to ground (called a 3 phase high leg delta connection), while the other two legs are 120V with respect to ground, so that you can operate 120V, 240V and 3-phase loads from the same utility service. The important thing is you should always measure before connecting equipment. 208V will fry most 120V electronics.


Are 220V and 240V the same?

They are not exactly the same.In the US, the term 220V and 240V are often used inter changeably. However, for the imported electronic devices which are specifically intended to work only on 220V may be damaged from running it on 240V.Most 220V devices will work fine on 240V. However, on some devices (mostly the ones do not have voltage regulator), it will cause over voltage for internal circuits, which lead to shortened life.Yes, they are the same thing and used in US residential homes. If you take two 120v lines, each being 180 degrees out of phase with each other, you get 240v. Sometimes 120v lines drop as low as 110v, so the terms "110" and "220" are representing the voltage drop.This is not to be confused with 208v, which requires three 120v wires instead of two, with each wire being 120 degrees out of phase. Typically, residential homes do not have three phase wiring, so don't purchase anything requiring 208v power unless you know for sure that it is available.220 to 240 voltagesYes, 220 and 240 volts are a nominal figure in the same voltage range. It is brought about by the power company, as they have a responsibility to keep voltages within a certain 10% range. The load will only notice a difference of 1% on the load current. e.g. Wattage load of 2400. Amps = watts/volts. 2400/240V = 10 amps. 2400/220V = 10.9 amps. On a constant resistance as the voltage goes lower, the current goes higher and vice versa as the voltage goes higher, the current goes lower.


Where is 120V 50Hz used?

Morocco, Vietnam, Neth. Antilles, and some Middle East countries.


Will a DVD made for 120V 60Hz work in 240V 50Hz if you use a voltage converter?

Maybe... most modern equipment will operate on 90V - 260V so it's worth checking before buying a voltage converter for it. If the DVD player is 120V, that suggests that it is North American and will play NTSC standard discs. Using it on a 240V region means it is likely that it will be in a PAL zone. THerefore, discs bought locally may not work because of regional codings, because of the difference between PAL and NTSC and because the display may not be able to handle NTSC. Some DVD players will play any standard (NTSC or PAL) and some displays will also handle either standard. A handful of players do not have region codes either. It is worth a little more research before you assume that the DVD player will perform as you hope.


Can you use a 120v appliance with a 240v supply?

It depends on what the appliance is. Some smaller appliances have a dual voltage switch which allows you to adjust the appliance to the supply voltage. Look on the manufacture's nameplate label to see what they recommend as a working voltage. There it will also tell you whether the appliance can be used on another voltage source. ==== Yes, you can. But it will fail ("burn out") almost immediately. If it's one that accepts either input voltage or if it has a little '120/240' switch on it, and you flip the little switch to the '240' position, then you're no longer talking about a "120v appliance".


Do all cb radios have to be pluged into a car?

No. Some carry batteries internally (handhelds), and some are wired for 120v power (base stations).