Thursday, 28 July 2011

What’s your mains electricity voltage?

I’m frequently astonished at how little I know and even the facts I do know seem to be changing…

  1. Whichever electricity supplier you use, I was certain that the mains electricity which we have delivered into our homes in the UK was universally 240v 50Hz. WRONG.

  1. Wherever we live in mainland UK, we all get the same mains electricity voltage. WRONG.

  1. Last try at known facts. Our mains electricity voltage, (whatever it is) remains constant through out the day and year. WRONG.

OK. After a little browsing on the internet it becomes apparent that I’ve got it wrong on all counts.

  1. Because we now import a significant amount of electricity from our European neighbours, we’ve harmonised to their voltage of 230v 50Hz.

  1. There are huge variations in the voltage supplied within the UK. If you live in Hampshire you may only have 213v and in the North East it could be 250v. The suppliers of your electricity are only required to deliver 230v +10%-6%. That means if it’s between 216v and 253v that’s fine. Obviously voltage variation has implications for the equipment we use in our homes. This may manifest itself in equipment running hotter than intended due to higher than expected voltage, or lights being dimmer than normal due to lower voltage. If the actual supply is higher than necessary for proper operation, the equipment will consume more power than needed, and in many cases life is reduced - both increasing the cost of ownership. The UK Government is of the view that “equipment placed on the market in the UK must be safe at the operating voltages which the equipment will find itself exposed.” That sounds like a very reasonable stance to take and if I’d seen signs of this policy being followed or even publicised I’d probably be reassured.

  1. Your mains voltage will vary throughout the day and year dependant on weather conditions and consumer demand. I measured mine at 9:00am and it was 243v, I repeated the exercise at 21:00pm and it had fallen 5% to 230v. Perhaps my intermittent poor signal strength on my TV isn’t based on aerial problems, it’s the power supply?  

I’m probably worrying unduly. I realised when we bought our first video recorder in 1986 that technology was starting to leave me behind. I have brief lapses into competence, but the trend is a downward spiral. Hopefully some fat cat bureaucrat better qualified than I am is sitting behind his desk ensuring all is well?

What's your socket producing?



  1. Hours of Fun for the kids over the summer:
    get a power meter like and get them to measure mains voltage regularly during the day and, between times, the on and idle power usage (and power factor) of every bit of electrical equipment in the house. (Well it might have worked for me :-)

    Up here in NE2 we're 250V most of the time, I see 248V pretty regularly and occasionally 245V.

    At work in SR2 we had continually high voltage as reported by computer UPSs complaining about 'over voltage' and switching to battery for part of most days. This has been mitigated by some (not very reliable) voltage reduction equipment (that kept tripping out and cutting all power!) and a new sub-station, presumably configured to current standards.

  2. @Chris B
    Hi Chris. I don't know about kids having summer fun in the North East. Here in the East Midlands we like to keep their noses firmly pressed against the waterwheel powered looms.
    I personally LOVE the idea of the energy monitor, much too good for kids.

  3. Our Gas engineer, as part of his duties when checking our central heating boiler, tested our electricity supply, and found it to be off the scale - in the red zone above 252 volts, which was as high as his equipment could read. We are based in West Yorkshire, so it seems according Chris B that perhaps that is normal for us? What do you think?

    We have several PCs and other sensitive devices between us, so is there a risk? I have lived and worked here for 26 years and its the first I have heard of this issue.

    1. Hi Elaine.
      I think you'll be fine, unless you get massive peaks of power. I still find it strange that we all assume electricity coming into our homes is at a constant value, whereas the reality for all of us is very different.

  4. The UK voltage is now 230 V +10% /- 6%, AC, 50 Hz. However, it's worth noting that this 'new' nominal voltage has been nothing more than a 'paper exercise' to comply with European harmonisation standards. In practice, nothing has been done to change it from the original UK standard, which was 240 V +/- 6%. (If you compare the allowable percentage variation for each standard, you will note that the range of allowable voltages is roughly the same!)

  5. Totally agree with Peter - harmonisation equals adjust % so all numbers fit. It is a great pity our existing voltage sensitive equipment does not like it.

  6. Mine was at 250+ , had a voltage regulator installed which has dropped it 10% and should also drop my bills as well. ( Ecomax Volt Reg)

    1. Hi Tim.
      I'd be very interested if you could provide some evidence that your voltage regulator really saves you money.
      Would you consider doing a "Guest Post" for us?

    2. I also would like to know how a voltage regulator dropping the voltage by 10% could reduce electricity bills. It might save some wear and tear on components that struggle to meet the 230 +10% spec, but as to saving electricity/money -

      I was was always taught that Amps(current drawn) = Watts / Volts i.e. 1Kw at 250v is drawing 4 amps whilst 1Kw at 220v is drawing 4.5 amps.

      A little googling threw up the following link that explains it much better than I can, but if your using electricity to generate heat (most things) the higher the voltage the better, if your running devices originally designed for 220 +/- 10 on higher voltages then they may fail sooner, if your running electrical equipment with their own internal power supplies (most of them) it makes no difference.

    3. The "inter web" is full of wired and wonderful sites (mine included). Take a look at for REALY odd electrical items.

    4. Possibly a year is too long to wait but only just saw these postings.
      1Kw will take 4A at 250v because of the resistance of the heating element, which doesn't change (hardly) with voltage or current. At 240 volts it won't draw more current but less, about in inverse proportion to the fall in voltage, so about 960w. So it will cost less; but it will heat less water, or the same amount slower.

  7. Hi SolarIcarus

    I don't have SPV but have a friend/neighbour (non computer literate) who does, and who shares the same electrical supply we do in the rural West Midlands which consistantly runs in the 246-254V range. A Google search turned up your blog.

    The reason for the search was that he had a south facing 4KW SPV system installed in 2011 by a very reputable local company, but this summer (a very good SPV one I understand around here) has been disapointed by the power generated. The installation company came in to check things out and reported that the problem was due to the SPV safety equipment frequently shuting off the connection to the grid because the grid was over voltage. The LDC have measured the supply over a period and say it is just within limits.

    So before deciding who's posterior he needs to kick he asked if I could find out anything on the "interweb".

    In a few technical forums you find quitea few comments like "information I've heard from installers of small (<16A per phase) Distributed Generation (DG) under the G83/1 Recommendations is that voltages exceeding the upper limit (ie 253V) are common"

    I spoke to an electrician friend who said he had heard of similar cases especially where the SPV panels and equipment were designed to European Spec a lot of which is still to the 230 +/- 6% i.e. an upper limit of 244V rather than 253V. They therefore were more prone to shut down when voltages went high, which coincidentally is on hot sunny days when power consumption is lower. Catch 22 !

    Wasn't looking for a solution here, but maybe the comment may help someone else with a similar problem. I have booked marked the page and If I find out what the solution is I'll try and remember to come back and update.

    1. Again sorry to be so late with this reply, don't suppose anyone is interested now, but our SPV set-up was so poor due to cutting out, eventually traced to high supply voltage OVER 264v, that the supply authority had to come and reset the supply to the village!