UK mains voltage

rich_jtg

Hi,

I don't suppose anyone knows what the voltage range of mains electricity in the UK is these days.

I was presuming that it was 230-240V, but the voltage in my mains supply is 254-255V which seems a bit high to me.

dougk_2

According to a couple of articles i read the following appeared :

"Today the mains is 230 volts plus or minus 10%" - so between 207 and 253V.

I guess when you add in the tolorence of the meter used to check the voltage (which can be 1 to 2%) you are likely to be "in the range", but very near the top end.

fairenoughclough

rich_jtg wrote:

Hi,

I don't suppose anyone knows what the voltage range of mains electricity in the UK is these days.

I was presuming that it was 230-240V, but the voltage in my mains supply is 254-255V which seems a bit high to me.

Use the meter you used to check your voltage to check somebody else's, the meter's probably out of calibration.

Hunnymonster

The nominal voltage in the UK is currently stated as 230V+10%-6% (216-253V) - although it used to be 240V±6% (225-255V) here and 220V±6% on the 'continent' (now they're 230V+6%-10%) - with a view to converging on 230V±6% all over at some unspecified point in the future.

The 230V+10%-6% is only a fudge to allow the voltage not to actually be changed but remain within specification - means your light bulbs burn brighter (and burn out faster) and your kettle boils faster than your continental neighbours

I've seen it at Christmas where the voltage has sagged to 190V on occasion - simply due to the load on the grid - the reverse is possibly true at this time of year when there's no load on it, the voltage does a 'reverse sag'.

rich_jtg

Thanks for your replies - much appreciated. I'd tested the supply with different meters, both showing an average of 254.6V.

I'm just wondering whether the high voltage could be connected to problems I've been experiencing with my electricity supply meter reading inaccurately?

Is there anything I can do to get the voltage lowered? I presume it can't be any electrical equipment in my house any good.

andy88_2

Did you test the voltage across an open circuit or a load? The impedance of the meter itself can affect the reading, though modern ones are higher.

The supply isn't doing any harm. Electrical equipment will have tolerances for this.

What are the supply meter problems? Why do you think it inaccurate? If you think there are problems in the house consult an electrician.

Hunnymonster

It'll certainly be blowing his lightbulbs about 10% quicker than otherwise - but they'll be burning about 12 brighter in compensation

Overrunning an appliance will shortent it's life - although how appreciable that shortening will be is debatable. Mention it to your electricity transport company (the one that your power provider tells you to ring in the event of a power cut) - preferably by letter - if it's that close to the endstop of tolerance, they should be able to modify the local supply to compensate (whether they will or not, is another matter entirely)

MGAstra

As somebody said earlyer, UK and rest of europe have changed to 230Vac. We used to be 240 and rest of europe 220V.

As for high mains degrading your appliances, I'd say yes definately try to get your supply reduced if you can! I design power supplies at my work, and we design them to operate reliably over 207Vac to 253Vac input. If you have any 'cheap' equipment (eg. typical sub £30 dvd player form far east) then it may not have been designed to such a high mains input spec.

Also, as the hunnymonster siad, your light bulbs will burn out quicker! (although I dont understand where the 10% less lifetime and 12% brighter comes from).

Please let us know if you manage to get your mains supply lowered!

Mark.

MGAstra

Just had another thought...

Are you using a voltmeter that states "true RMS"???

I suspect that your meter is assuming your electricity supply is a true sine wave, and calculating the 254-255V reading based on that.

The mains supply isnt actually a sinusoidal waveform (-check it on a scope, carefully). Most electical devices these days have switching power supplies (due to efficency) so there is a bridge rectifier and smoothing capacitor at the input. This means that current only flows into the device during the peak of mains. The net result of this is that no load flows during most of the cycle, then as the peak approaches, lots of current is draw and this makes the peak reduce. Hence, it looks more like smothed sqaure wave. The true rms will most likely be more around 230Vac :T but basic voltmeter would assume the wave is sinusoidal and hence assume a higher peak, which then gets calculated to be a higher rms value. :rotfl:


Mark.

[Deleted User]

Firstly andy88, meter impedance will reduce the voltage you measure, not increase it, and the effect that even the most insensitive meter will have is measured in microvolts, not volts.
Secondly MGAstra, Have you stopped to calculate how much you would have to clip off the top of a sine wave to change it's form factor by this much? Assuming the RMS of the clipped sine is still 240V, you'll need a form factor of 240*1.1107/255=1.045. To change the form factor by this much you would need to crop the top 60% off the sine. If the RMS were 230V as you suggest, you would need a square wave to give a reading of 255V on a mean sensing multimeter!!!
No appliance has a power supply big enough to cause this amount of distortion, and even if it did, how would the board be able to raise the supply voltage to compensate when everyone is using different appliances?

MGAstra

jack_pott wrote:

Firstly andy88, meter impedance will reduce the voltage you measure, not increase it, and the effect that even the most insensitive meter will have is measured in microvolts, not volts.
Secondly MGAstra, Have you stopped to calculate how much you would have to clip off the top of a sine wave to change it's form factor by this much? Assuming the RMS of the clipped sine is still 240V, you'll need a form factor of 240*1.1107/255=1.045. To change the form factor by this much you would need to crop the top 60% off the sine. If the RMS were 230V as you suggest, you would need a square wave to give a reading of 255V on a mean sensing multimeter!!!
No appliance has a power supply big enough to cause this amount of distortion, and even if it did, how would the board be able to raise the supply voltage to compensate when everyone is using different appliances?

Firstly jack_pott, I havent stopped to calculate anything - I just made a suggestion! :eek:

Secondly, where does 1.1107 come from??