Reading the list of standard plug and socket types on Wikipedia, I see that countries have made their mains voltage higher or lower.

For example, in Mainland Britain (Wales, Scotland, England) the voltage has been lowered to 230V from 240V. On the other hand, in Northern Island it has increased from 220V to 230V.

Have they just moved the voltage to informally meet the rest of the world? As the vast majority of countries are either 230V or 120V.

Are there any other things that could be gained from this? I understand that lowering the voltage could decrease power dissipation because \$P=VI\$, but increasing the voltage? What is there to gain other than more losses?

  • \$\begingroup\$ I read something last year (or the one before) in IET's E&T magazine about it being related to I^2 R losses but I can't remember any more than that - hopefully someone can chime in with an answer \$\endgroup\$ May 22, 2011 at 10:09
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    \$\begingroup\$ Losses would be decreased by increasing the voltage, which is why power lines run at thousands of volts. Assume the power delivered to the load is constant. If you use a higher voltage to send it, the current decreases, and the I²R losses in the wire are lower. \$\endgroup\$
    – endolith
    May 22, 2011 at 12:34

4 Answers 4


It is to standardise everything on a single fixed voltage. But in practice, mains voltage isn't 230V. It is standardised at 230V +10% -6%, or 216V to 253V. Here, mains voltage measures 249V, which is on the high end of the scale - but we're on a small farm road with not many other customers. Away from home I have measured it at 233V, due to resistive losses from greater demand. Countries have not changed the actual voltage - that would require changing all the generators or all the transformers in the country (at a substantial cost), merely, the allowable range has changed.

  • \$\begingroup\$ Note that the tolerance are not always that well strived. I have heart some stories about factories or farms in desolate places only getting 180V AC. I assume they are on the end of the phase line with some heavy users in their area. \$\endgroup\$
    – Hans
    May 22, 2011 at 17:57

Europe switched from 220V to 230V in the nineties. Advantage: you need less current for the same power, making that you need less copper for distribution, but it's only 5%. And if increasing the voltage offers an advantage it can't be an advantage in the countries where the voltage is decreased.
IMO it's been done to have more of a standard. Nowadays you can have universal power supplies which are as happy with 115V as with 230V, but in the past a 220V appliance may have had a switch to select between 220V and 240V. Now that everybody uses the same 230V you don't need that anymore.


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    \$\begingroup\$ I remember once blowing an adapter of my NES by accidentally choosing 110V when it should have been 220V. :( \$\endgroup\$
    – 0xakhil
    May 22, 2011 at 12:29
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    \$\begingroup\$ If you downvote can you please tell us why? \$\endgroup\$
    – stevenvh
    Jul 31, 2012 at 13:55
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    \$\begingroup\$ I guess the downvoter thinks that the cartoon character's face shouldn't be charred since he has suffered a finger-to-finger direct shock ;) \$\endgroup\$
    – MikeJ-UK
    Jul 31, 2012 at 14:01
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    \$\begingroup\$ @Mike - The cartoon doesn't mention it, but that guy is/was the coal-dealer, so his face has to be black! \$\endgroup\$
    – stevenvh
    Jul 31, 2012 at 14:08
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    \$\begingroup\$ FWIW 8 years on - it's not 5% - it's 10% due to ~= I^2 heating effects. \$\endgroup\$
    – Russell McMahon
    Sep 9, 2019 at 7:15

In my experience higher voltage is a disadvantage for the user because light bulbs tend to have shorter life with higher voltage. I would prefer AC in the lower specification range for that reason and since the power output from appliances is seldom of concern.

The only exception I can think of would be mains powered tools like a chain saw.

  • \$\begingroup\$ Can you provide reference about the life shortening? It seems a pretty general statement, considering all the different types of lightbulb on the market. And it seems a little portion of all the possible utilities. \$\endgroup\$
    – clabacchio
    Mar 21, 2013 at 14:44
  • \$\begingroup\$ @clabacchio: Light bulbs are most efficient and give off the best light when they're heated almost to the point of immediate failure. As the temperature is reduced below that point, bulb lifetime increases immensely. Things like movie lights are operated hot enough that they only last a few hours; general-purpose light bulbs sold in the US burn cooler, and have historically been designed to last about 700 hours. Many so-called "long-life" bulbs are simply 130-volt bulbs which, if operated at 120 volts, will last several times as long. \$\endgroup\$
    – supercat
    Mar 21, 2013 at 16:26
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    \$\begingroup\$ @supercat this is for incandescent bulbs, but what about CFL and LED bulbs? Especially the last ones, I'd expect them to be regulated, so it shouldn't matter much. Also, given the previous answer it seems that there's no real change in mains voltage. \$\endgroup\$
    – clabacchio
    Mar 21, 2013 at 16:29
  • \$\begingroup\$ @clabacchio: Electronic power supplies adapt, yes, that is how they work. I used to have a rechargeable shaver with an input spec of 12 - 250 AC/DC. Yes, 12 as in car battery at the low end. Those German people are clever (Braun). \$\endgroup\$
    – user56384
    Sep 2, 2015 at 22:36

There's an interesting issue hinted at in this question. P does equal V*I, so for resistive loads, if you up the voltage 5%, you are also raising the current 5%, yielding a 10% increase in power. But for a regulated power supply, the output won't change, and the power consumption won't either. On the input side of that supply, the current will decrease when you raise the voltage. They used to lecture us about appliance motors under brownout conditions, so I have to assume these motors exhibit the same property.

If you are the power company, you would have to do some figuring to determine whether your power output would increase or decrease by changing the voltage. While I suspect that light bulbs do not account for the majority of power use, I also suspect they have a bigger headache dealing with reactive power, from those appliance motors and non-power-factor-corrected power supplies out there.

  • \$\begingroup\$ (1) Probably easier for the power company to just change the voltage and then measure the effect. (2) Regulations regarding power factor of power supplies are attempting to fix that particular problem. \$\endgroup\$
    – gbarry
    Mar 21, 2013 at 14:50

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