Why does UK/USA use 110/120V and others use 220/240V

My girlfriend asked me this question this morning and since I explained it to her, I though why not write an article and explain to everyone of you about why does USA/UK use 110/120V and others use 220/240V.

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.)

So the answer is that both ‘some of the world’ and the U.S. distribute 240 volts to homes, apartments, shops, offices, and many other types of buildings.

It seems like the difference you are talking about is that on the non-U.S. systems, their receptacles are 240 volts, while ours are 120 volts. One reason is that lower voltages tend to be safer, which is why you are receiving 240 volts at the home instead of the thousands of volts generated by the power plant.

In terms of power production – all power is the same. It is then transmitted over High Voltage cables – usually above 10K Volts. The power is then stepped down before it reaches our homes.

U.S, Japanese and some other countries receive 110V in the form of 2 wires – 1 Live and 1 Neutral
Some may argue that the US is behind or has just managed to stay afloat with this old system longer.
The US is at 120 volts, not 110 volts. It was increased sometime around the 1950s.

The historic reason for 110 volts was due to the DC power systems created by Thomas Edison. I think he chose 110 volts because that is what his light bulb worked on. Later on these systems were converted to AC so you didn’t need a power plant on every corner but the voltage wasn’t changed so existing lighting didn’t need to be replaced (they didn’t care if they got AC or DC)

An interesting question is why the rest of the world did start using 110 volts. How did 220/230/240V get started over there? 
The US system theoretically could be made as good as (slightly better, actually) than the European system with no infrastructure change, except to houses themselves. 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.

As one has stated above, it was Thomas Edison who promoted the use of (then) 100 volts as some tragic experiences in the early days of power distribution showed that 100 volts was not usually lethal for a shock. Remember that in the early days, bare wires were strung though ceramic insulators, both exterior and interior, and so there were many more shock hazards present. As technology advanced, good, long life insulation was wrapped on conductors.

Speaking from personal experiences, one as a child, I am glad that the few shocks I’ve experienced were with 120v., not 220v. power.

Just remember it’s not the volts that kill, it’s the current (the amps).
Yes, but at 240 volts your body’s resistance will draw twice the current and that may well be over the threshold to kill you. In countries in Europe and elsewhere, where 230 volts is the general standard mains supply voltage for domestic houses, offices, factories, etc., they have to make sure that their wiring systems are very safe by using high quality insulation and wiring methods for all wiring upgrades and new work.

For additional safety the most recent wiring regulations insist that a Ground Fault Current Interruptor (GFCI) or a Residual Current Device (RCD) must be included in the main Consumer Distribution Unit (breaker box in US parlance) to cut the supply very quickly if any significant difference is detected between the currents flowing in the live (hot) and neutral wires.

An RCD works in a different way to the original very simple Ground Fault Current Interruptor (GFCI). An RCD will trip if there is any significant difference between the currents flowing in the live (hot) and neutral wires. A simple GFCI would trip only if any significant current is detected flowing in the main Earth (Ground) wire to the actual Earth (or Ground) spike. Note: GFCIs now operate exactly the same as RCDs.
In up-to-date domestic installations in the UK no actual Earth “spike” is used. Instead the protective safety wiring (or casing) of the incoming mains supply cable is used because that is most likely to be reliably “grounded” to the Earth.

That is different to US and Canadian standards and other countries’ which use the same. In those countries the incoming mains supply is two “hot” wires supplying 240 volts balanced around “Ground Potential” which is always 0V. (Zero Volts). An Earth Spike is used at each property (house, apartment, office, factory, works site or whatever) to provide a common Neutral (i.e. the “White” wire) for the two resulting 120 volt “hots”. One “hot” is coloured “Black”, the other one is coloured “Red”

The Second explanation is:

The existence of the various standards has been largely the result of local politics and historical accident

The system of three-phase alternating current electrical generation and distribution was invented by a nineteenth century creative genius named Nicola Tesla. He made many careful calculations and measurements and found out that 60 Hz (Hertz, cycles per second) was the best frequency for alternating current (AC) power generating. He preferred 240 volts, which put him at odds with Thomas Edison, whose direct current (DC) systems were 110 volts. Perhaps Edison had a useful point in the safety factor of the lower voltage, but DC couldn’t provide the power to a distance that AC could.

When the German company AEG built the first European generating facility, its engineers decided to fix the frequency at 50 Hz, because the number 60 didn’t fit the metric standard unit sequence (1,2,5). At that time, AEG had a virtual monopoly and their standard spread to the rest of the continent. In Britain, differing frequencies proliferated, and only after World War II the 50-cycle standard was established. A mistake, however.

Not only is 50 Hz 20% less effective in generation, it is 10-15% less efficient in transmission, it requires up to 30% larger windings and magnetic core materials in transformer construction. Electric motors are much less efficient at the lower frequency, and must also be made more robust to handle the electrical losses and the extra heat generated. Today, only a handful of countries (Antigua, Guyana, Peru, the Philippines, South Korea and the Leeward Islands) follow Tesla’s advice and use the 60 Hz frequency together with a voltage of 220-240 V.

Originally Europe was 120 V too, just like Japan and the US today. It has been deemed necessary to increase voltage to get more power with less losses and voltage drop from the same copper wire diameter. At the time the US also wanted to change but because of the cost involved to replace all electric appliances, they decided not to. At the time (50s-60s) the average US household already had a fridge, a washing-machine, etc., but not in Europe.

The end result is that now, the US seems not to have evolved from the 50s and 60s, and still copes with problems as light bulbs that burn out rather quickly when they are close to the transformer (too high a voltage), or just the other way round: not enough voltage at the end of the line (105 to 127 volt spread !).

Note that currently all new American buildings get in fact 240 volts split in two 120 between neutral and hot wire. Major appliances, such as virtually all drying machines and ovens, are now connected to 240 volts. Mind, Americans who have European equipment shouldn’t connect it to these outlets. Although it may work on some appliances, it will definitely not be the case for all of your equipment. The reason for this is that in the US 240 V is two-phase, whereas in Europe it is single phase.

Roughly speaking, to operate a particular appliance requires a particular amount of POWER, which (at least for resistive loads) is current times voltage. If you double the voltage, you draw half the current to achieve the same power. The primary advantage of lower current is that you lose less power in the wires feeding current to the appliance (or you can use smaller, cheaper wires for the same power loss rating). On the other hand, the higher voltage is somewhat more dangerous if accidentally touched or if there is an accidental short circuit. Some experienced electricians are relatively casual about touching 110 V circuits, but all respect 230 V. (This constitutes a “don’t-try-this-at-home thing, though–it’s quite possible to get a fatal shock or start a fire with 110 V!) Current trends are toward the use of even lower voltages (24 V, 12 V, 5 V, 3.3 V…) for any devices which don’t draw much total power to increase safety. Power is rarely distributed at these lower voltages; rather it is converted from 110 V or 230 V by a transformer at the earliest opportunity. Even in North America, 220-240 V is commonly used in residential appliances for
most high-power electrical appliances (ovens, furnaces, dryers, large motors, etc.) so that the supply current and supply wire size can be smaller. Higher power industrial applications often use 480 V or more. And, of course, transmission lines use progressively higher voltages as the distance and total power go up (22,000 V for local distribution to 1,000,000 V for long distance lines).

via: Some content via StraightDope

Supplementary Reading: [1], [2], [3]

  • Happy Fox

    Where the f… did you get this from ? Half the article it’s just completely wrong, really genuine misinformation. Why do you embark on explaining for others, like some expert, things that you obviously have no clue about ? For starters they don’t have 110 volts in UK. But there are so many other wrongs, I don’t have time to mention them all. Take it down, or continue to make a fool of yourself.

    • pf3

      Huh? Did you read a different article?

    • V Nats

      There is only one fool here and that’s you. Learn to read.

      Plus the whole, “So many other wrongs, I don’t have time to mention them all, blah blah” is priceless. I’m sure you’re a very busy child.

      Silly troll.

      The article is very good.

      • Thomas Mills

        You mean apart from the fact that the UK doesn’t use 110V?

    • Geoff

      I would like to know where you all get your biased brainwashed information from.
      240/415V transmission system is so far superior.. Double the voltage / halve the current…. Far less heat production, less fires.
      Double the transmission distance, less current, less fires
      The U.K. Europe and Australia use 240/415 for best safety and reliability of transmission.
      RCD’s are installed to detect potential current differences generally at 30mA/30mS. To protect people. Try looking at a GFI in USA and find its trip rating, it is not listed. Latest standards now call for fault loop impedance, this test calls to ensure the earth/ ground wire is sized to accomodate the cable is sized to ensure the fault current is taken into account to trip the breaker installed.

      To summarise, Edison was a fraud, he only patented the light bulb and Tesla only was trying to facilitate the already running (20 years earlier) European system..


      240V – life safety, lower current.
      120V – Lower touch potential, higher current , higher fire potential


      • Joe

        Pretty sure GFCI’s are required to trip at anything over 6mA.

      • manxman1

        20v can kill you if you have a weak heart. In UK they don’t allow live testing.

      • Dan

        240V is not safer to touch… it’s lower current for a appliance that is working correctly. If you touch 120 or 240 with the same location & pressure on your skin… the 240V will be double the current.
        If you pierce your skin with a single strand of either your skin’s resistance is lost and the liquid of your body can easily pass the few milliamps required to stop your heart (if the path to return is through your chest.)

  • max

    WTF, the UK doesn’t use 110V ?

  • Stel-1776

    You may want to look into 50Hz (Europe) vs 60Hz (US) and see why the European system is far less efficient. Tiny voltage drops over short 120v lines within a home or neighborhood are not much of an issue. 240V is never safer than 120v.

  • Timothy De Young

    A small thing, but I think that GFCI means “Ground Fault Circuit Interruptor”, not “Ground Fault Current Interruptor”.

    • John

      You are correct, but both things you said mean the exact same thing :p if the “current” is inturrupted there is no longer a live circuit :)

  • Calvin Hodgson

    This article is hard to read and confusing. Many times it mentions “110 V” and “230 V.” I don’t know if I missed something but I sure as hell ain’t re-reading again. You jump from one idea to the next with very little transition. many of the parenthesis are downright confusing.

    I learned a little but felt like I wanted to go stuck my dick in a 240 V socket.

  • CarlG17

    the 50/60hz thing is way overblown, the use of 230V in europe more than compensates, in addition most of northern europe (UK excepted) has common residiential 3-phase (400V) which is used for heavier equipment like stoves and home workshops.

    • manxman1

      UK uses 415v for industry.

  • Terah

    You can’t just add 120v + 120v…measuring between the two ‘hots’ wouldn’t be 240v unless their phases are shifted 180 degrees. When measuring between 120v and 120v on the same phase, you get 0, and if the power company accidentally installed two phases that are only 120 degrees apart, you’d get no higher than 208 volt, so explaining the existence of 240v in a residential home by calling it “the sum of both 120 volt conductors (240 volts)” is a gross over-simplification at best.

    Europe, at least the Netherlands and Belgium, never had 120 volt. A dual system was in place with the lowest voltage being 127 volt (phase to neutral – resulting in a phase to phase voltage of 220v) until the 70’s, after which every household was switched to 220v (phase to neutral).

    All in all a pretty incorrect article, alas.

  • CarlG17


  • Arne

    The UK actually uses 240V, like pretty much all normal countries.

    I live in Belgium, so I’m surrounded by the NL, FR, DE and the UK. They all used 110V a long time ago. But we have so many electrical appliances right now, that 110V just isn’t enough.
    My brother moved to the U.S. and he can only use 1800W on one circuit. My European vacuum is 2200W, my frying pan 2400W, …
    We can use about 3500W per circuit. We have 400V lines for things that draw a huge amount of power, like a furnace, or electric oven, just because you’re consuming more power when using a certain device on different voltages.
    Charging your laptop in the US with a 110V power supply will require more power than charging it in Europe with a 230V power supply, for example.

    Plus: 240V is actually safer. The wires produce less heat because it’s less likely to have the maximum capacity going through. And you won’t get shocked: European plugs are designed in a way you can not get shocked while plugging something in, compared to the U.S. I noticed you can sometimes even see the metal prongs when something’s plugged in in the U.S. That’s dangerous as fuck.

    The European standard is 230V, but most houses get about 240/245… Just because the voltage drops when you’re using power. It may drop about 20V, and everything would still work fine. A 20V drop in the U.S. would cause a lot of devices to stop working.

    And if we use a freaking long extension cable, and connect something like a computer or TV at the end of that cable, it’ll still work, even though we may only get like 180V. Just because a lot of appliances work in with everything in between 110V and 240V.
    If y’all do that, you pretty much wouldn’t have power anymore, at all.

    I really think 110V isn’t enough anymore, these days.
    My brother’s U.S. washer is junk, just because it doesn’t heat the water, it just uses the hot water line (which doesn’t get that hot…).
    We have enough power to power washers with heaters inside of them (I’ve never even seen washer without heaters until I went to the U.S.).

    The U.S. is a beautiful place, but they’re quite a lot of steps behind of Europe in a lot of things.
    We’re just so much more modern in a lot of things.
    (Not hating the U.S. though).

    • mark

      The 230 V system is indeed good, however that doesn’t mean the 120 V system is bad, unusual or outdated. Keep in mind that while more countries use 230 V, more than 40 countries using 120 V type of systems (including 5 of the world’s largest economies) is nothing to sneeze at. Also, voltage in the US and other countries has been 120 V for many years now, similar to how the EU harmonized to 230 V. I’ll now comment on each point you’ve made, citing the other comment I just posted when necessary:

      1.No European country has had a 110 V system. What some countries had was a dual 127-220 V system.

      2.As long as loads placed on a circuit are within the range it was designed for, 120 V is more than good enough to run most appliances. The Japanese have done extremely well on their 100 V system. Larger equipment that run more efficiently on higher voltages like water heaters, clothes dryers and air conditioners are plugged into dedicated circuits with dedicated plugs and outlets (you can look up the NEMA connector standards if you want to know more). For smaller appliances that have a heating element like kettles and frying pans the difference in output really doesn’t make a difference to most people; they heat up as much as needed in a reasonable amount of time, waiting a couple more minutes is not a big deal. For vacuum cleaners it matters even less, they start up just as fast and vacuum just as well.

      3.Chargers produce the same amount of power as long as the input voltage is within range which for most chargers is 100-240 V 50-60 Hz. No additional current is needed to run on 120 V.

      4-Any electrician who knows what they’re doing will always keep safety margins in mind. That’s why thicker conductors are used for house wiring in 120 V systems.

      5-Sleeved prongs really are a safety feature all plugs should have, but 120 V plugs and sockets are far from being death traps. Flaps around the prongs and where the cord enters the plug as well as ribs and dips on the plug itself all keep your fingers from slipping towards the prongs. You are safe as long as you exercise common sense.

      6-Voltage drop is neither more nor less of a problem in 120 V countries than it is elsewhere. Most 120 V homes have split phase wiring that requires transformers to be closer; not much voltage is lost (if at all). Larger installations use three phase wiring similar to Europe and other parts of the world, where transformers can be placed farther apart without losing much voltage so you obviously still get something very close to 120 V. Worst case scenario most 120 V appliances can run on at least 100 V (see Japan reference above).

      7-Trying to run a 230 V appliance on 180 V efficiently is like trying to start a diesel engine with water. It’s simply not going to happen.

      8-Your brother’s washer being a piece of junk has nothing to do with it running on 120 V and everything to do with it just being a piece of junk. Can be fixed by getting a new one or moving to a place that has a better one. Washers with built-in water heaters (also available in the US therefore totally usable at 120 V) are cool but considering we now have HE detergents, a wide variety of stain removers and the fact that many people are cutting down on energy consumption, it’s not a must have feature.

      9-Europe has made great advances in big things like transportation, public healthcare and education, social justice and smaller things like EMV cards (thankfully adopted in the US and many other countries). However, anyone coming from the US or any country that follows similar economic models and lifestyles will find Europe’s limited business hours, limited selection of certain products, lesser use of credit cards in certain countries, more complicated and far-reaching bureaucracy, a certain island country’s inability to deal with snow, lack of basic comforts like air conditioning, and so on, to be very outdated and unexpected from generally very developed countries. Don’t mean to hate on Europe, I go there every few years and it’s always a very pleasant experience. No country or region has all the answers. We all have a lot to learn from each other. The only way to do that is to keep our minds and lines of communication open.

    • If you have a quality hot water heater, your hot water can get very very hot, unless you set the thermostat on the water heater to something lower. So your brother’s U.S. washer is not necessarily junk just because it doesn’t heat its own water. After all, if you have a good water heater (which often uses 240 V, by the way), you don’t actually need a heater in your washing machine. In fact, why would you waste electricity heating water in your washing machine when you have a tank of hot water meters away?

      Based on your logic, if a U.S. washing machine is junk because it doesn’t heat its own water, your home’s water heater is junk if you need a water heater inside your washing machine since the home’s water heater is not enough.

      Basically here is how it breaks down:

      Good Home Water Heater + No Heater in Washer = Hot Water
      Weak Home Water Heater + Heater in Washer = Hot Water (at least for washing clothes, not for showers)
      Weak Home Water Heater + No Heater in Washer = Warm Water = Your Brother Home
      Good Home Water Heater + Heater in Washer = Hot Water = Redundant

      Your brother probably had a crappy home water heater, or had the thermostat on the water heater set too low. It’s not the washer that’s junk.

      • Jojo

        To be intellectually honest, having “Good Home Water Heater + Heater in Washer” is not necessarily “Redundant”.
        You can have different temperatures for both and it’s usually the case. The washing machine( with heater) in Europe can go up to 90 °C (194 °F). The idea is to only heat when the specific appliance needs it. Because I don’t need my home heater to maintain all day that high temperature level. You don’t do anything with that temperature, it’s too hot (except washing clothes, and other few things I guess).
        So it saves energy, it saves money. It’s heat on demand if you will.

        So to not have a heater in washer is :
        – depending on home water heater (if it breaks down, it affects everything that need hot water. ok it’s rare I give u that.)
        – wasting energy by having high home heater temperature just to accommodate the occasional washer cycle needs ( waste of energy the rest of the day)

        If you follow my logic, the best setup would be Home Water Heater + Heater in Washer ( with 2 inputs : cold and home heater water). In that case, the washer could use the already warm water of the home heater and heat it more if it needs to).

        I don’t think this type of washer exists in US or EU but it would be the best of both world 😀

        But for the time being, it’s better to heat from cold water for a short period for an appliance then keeping super hot water all day.

    • Siegfried

      Looks like you are one step too far – from comparing the electricity voltage, you jump in t concluding that USA is behind Europe. It took me a few years after moving to USA to realise that actually Europe is behind in many other things. And for quality of life, common sense, and practialities the winner is … USA (except for the banking system!).

  • mark

    Quite a few things wrong with this article:

    1.The UK doesn’t use 120 V nominal (phase to neutral) voltage, it uses 240 V thus falling into the 220-240 V group. They do have lower voltage options for use in high risk environments such as center tapped 110 V (55 V to ground) transformers used at construction sites and their shaver sockets (the only type of outlet allowed in bathrooms) sometimes have a 115 V receptacle or a step down switch.

    2.Possibly a typing mistake, but the US system was originally 110 V not 100 V. Japan does use 100 V because 100 falls into the sequence of the metric system which they adopted at roughly the same time they built their power grid.

    3.No European country has ever had a 120 V system. A few countries (off the top of my head: the Netherlands, France, Italy, Spain, the Soviet Union) had a three phase system where phase to neutral was 127 V and phase to phase was 220 V. Since about as many appliances would run on 127 V as on 220 V they effectively had a dual system. They all changed over to 220 V phase to neutral in the 70’s and later on to the current 230 V standard (except for Russia which still uses 220 V).

    4.With ever increasing levels of safety and efficiency in modern electrics, the 120 V vs 230 V debate is pointless. The differences in output are not significant enough to render 120 V appliances ineffective, the shortcomings of the 50 Hz line frequency are compensated by the 230 V voltage, electronics will produce the same amount of power regardless of input voltage as long as it stays within a specific but wide range (reason why most chargers work on 100-240 V 50-60 Hz) and how safe an installation or equipment is depends on whether safety guidelines are followed and not the actual voltage. At the end each system is only as good as its regulators, builders and users.

    • gvel

      The European systems are by no means all the same, not even within the same country. In many areas of Norway, for example, it’s 230 V phase to phase (delta).

  • Nasreen Zahida


  • Sunrise250

    While I accept everything said in the above article there was little mention of the importance of copper in the early distribution of electricity. This is important because the reason the Guggenheim family (fairly suddenly) became the richest in the US was that, in the 1800’s, before the electric revolution, they had accumulated copper mines all over North and South America. Europe did not have access to such copious amounts of copper. Transmitting current over copper required half the diameter to get a 220V result even though this voltage was definitely dangerous for general domestic use – light sockets, living room/kitchen/bedroom sockets, radios, etc.
    In the US the price/supply of copper was not an obstacle so 110V was a no brainer to use in households and not a problem to install at all levels of transmission.
    I had always understood that metric-centric Europe went with 50Hz and the importance of one of the first main uses of electricity being the electric clock caused the US to choose 60Hz (maybe not correct) and it was only later it was realized that 60Hz was superior. [These separate frequencies also created another clash of standards… as artificial light was component of TV video recording these frequencies gave rise (ac/frame rate phasing) to originally incompatible PAL and NTSC video standards on respective sides of the Atlantic etc.]

  • RobS

    Dhawal D, please correct your article. Both the title and at least some of the content is completely wrong, for example the UK does NOT use 120V, it uses 240V. Some of the comments also point out mistakes with your article, and yet you have neither responded to the comments nor attempted to correct the article. What is particularly frustrating is that all of this misinformation appears near the top of many Google searches.

  • John

    people don’t discuss, some of the comments here are so disrespectful. I guess that’s what you guys are all about. The article was a good read we don’t need to have every fact perfect we get the idea. We leave knowing more than we came with. But the comments I see I wish these people would just grow up. Unbelievable

  • silphium

    The US 240 V is not two-phase it is split-phase.