# 255v on an English Camping Site



## Diver (May 15, 2005)

Can anyone tell me how mains electricity might be distributed around a 50 hook-up site?

I’m on Wood Nook Camping & Caravan site in the Yorkshire Dales with a friend who has a StirlingPower ProCombi Q Inverter/Battery Charger unit. It isn’t working properly and so I started measuring the voltages in and out of the unit.

The incoming mains is fluctuating around 250 volts. When it reaches 255v the Stirling unit cuts out – which it should do.

I’ve reported this to the site owner. His incoming voltage is about 230v – as expected. 
He has checked and can see the voltage at the distribution points is over voltage. 

He has gone away to call an electrician friend but meanwhile I was wondering how do they distribute the mains in such a way that the voltage can rise so much?

Diver


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## geraldandannie (Jun 4, 2006)

How strange.

Found this:


> Originally, the UK mains voltage supply was specified at 240 v RMS +/-6%. Some while ago, the specifications were changed (230 v +10%, -6%) to allow harmonisation across Europe. The average value clearly indicates 240 v


So, originally, mains was allowed to rise to 254.4V, and now it's 253V. 255 is slightly over the limit. It's not much outside the limits, and you'd probably need to check it with different measuring devices. Multimeters have a tolerance on their measuring accuracy.

How it's distributed varies from site to site, I'm sure, but I'd worry if you were measuring a 25V difference, with reliable equipment, on the same site.

Can't really help much apart from that, I'm afraid.

Gerald


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## Diver (May 15, 2005)

Re-checked down at the office and the voltage is now 245v. So it would appear that it is the incoming supply that is out of control. The site is on 3-phase so I suppose we could be getting different readings across the 3 phases.

We have checked our readings with 3 meters and get the same. I would have thought that incoming mains should be between 220 and 240 volts and so anything in the region of 250 volts is excessive and could be damaging equipment.


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## sallytrafic (Jan 17, 2006)

The rules are as Gerald quoted. Campsites have a real problem. First of all they are largely rural which often means long transmission lines and volt drops before the supply even arrives at your door. 

The top end of the voltage is out of your control it depends on the supply company and their transmission lines and transformers. 

The bottom end is where the design of the circuits can influence things. As well as the actual voltage there is also a rule that an installation cannot drop more than 4% of the voltage applied .

All mains equipment should be ok at 253V


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## Diver (May 15, 2005)

So are Stirling being too conservative? 

The spec gives over volt trip at 253 and re-engage at 243. Both +/- 4%


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## geraldandannie (Jun 4, 2006)

Diver said:


> So are Stirling being too conservative?


Hard to say, really. Strictly speaking, they are correct. But, as a electrical / electronic designer for over 25 years, I would always allow a little bit extra into the specification, especially considering the environment in which they would be used. If the mains spec was 254.4, and is now 253, I'd have put over-voltage controls at 260 (always ensuring that the equipment would function correctly at that 260V level, or slightly beyond.

It sounds like you've been diligent with your measuring. Definitely worth the question of the site owner. The problem is that it will fluctuate anyway, so when the electrician arrives, it could be well within spec again. You could well be getting an imbalance between the phases, which is likely given that the installation probably balances the outlets between the phases, but not all outlets would be used at the same time, or to the same extent. However, this wouldn't give you your over-voltage readings. As stated before, the specification of the supply on delivery to the site should give you maximum readings of 253V now. The assumption would be that loads on the supply would drag this down, especially over the area of a 50-pitch campsite. however, putting an over-voltage trip at exactly 253 would seem to be a little imprudent to me.

Gerald


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## Diver (May 15, 2005)

While we were out a person from the Electricity Board came and measured the voltages at 253, 255, 255 at the transformer. He is arranging for a data logger to be fitted to see what is happening over the course of a week.


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## nicholsong (May 26, 2009)

This is the sort ot thread with knowledgable contributors which makes MHF worth its weight in gold.

Thanks to Nuke for setting it up, and to all those with knowledge who freely contribute.

Geoff


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## bigfoot (May 16, 2005)

What affect would this have on those of us with Electrobloks fitted?


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## geraldandannie (Jun 4, 2006)

bigfoot said:


> What affect would this have on those of us with Electrobloks fitted?


Dunno. I would hope that they weren't so tightly toleranced, so they could stand a little bit of over-voltage. I'd have to check the specifications - it will be in the book somewhere.

Even if it was spec'd at 255V, I would expect the designers to allow a certain leniency on that, to withstand 260V or so.

Gerald


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## sallytrafic (Jan 17, 2006)

High voltage is not unknown, for example on new housing estates or at night. Voltages of around 270V are often reported. It is possible for the supply company to alter tappings on the final transformer to adjust this but they do so with extreme reluctance. It involves turning off the supply which is a nuisance and then having done that the risk is at peak demand the voltage will fall too low and there will be a brown out. Motors especially do not like low voltage they turn slower generate less back emf so the current rises further even though the voltage is falling. Fires start that way.

The regs that the supply company work to are a nightmare to follow compared with the 17th edition wiring regs. Many electricians believe they make up the rules to suit. 

Technically when the voltages were harmonised across Europe to 230V the supply should have been turned down a bit. I don't believe it was. 

Another thing to watch out for is the waveform. When generated you have a perfectly formed sinusoidal waveform. 230V is properly described as 230V RMS (Root Mean Square), measuring that directly is difficult so most meters cheat they measure the peak and assume the waveform is a sinusoid, then display a calculated RMS. So for voltage a 230V RMS has a peak to peak voltage of about 325V, this is what is measured (or half of that) and then the formula is applied within the meter to give 230V. This only works with a single frequency sinusoid. 

When circuits are lightly loaded with things like computers then harmonics are reflected into the supply distorting the waveform. Now converting peak to RMS doesn't work 

To find out exactly what is happening you need a true RMS meter and an oscilloscope.

However for various other H&S reasons* using a multimeter to measure mains voltage is frowned upon. There are purpose built testers and data loggers for the purpose. 

*Anyone who has tried to measure 230volts when their meter was set to amps will know where I am coming from. If you are lucky and your meter is a good one you will only blow an internal fuse. Unlucky you get to spend some time at the undertakers.


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## nicholsong (May 26, 2009)

Frank

Very interesting. When you write abiut 'meters' and waveform are you only referring to test meters or does the same apply to domestic consumption meters?

Is so, and we are charged by the Watt, and W=V X A are we being overcharged if the supply exceeds 230V for the same Amps?

Or am I going in leaps and bounds down the wrong path? - qiuite possibly!

Geoff


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## johnthompson (Jul 29, 2010)

Kielder area in rural Northumberland has this week had an over-voltage spike that has taken out lots of electrical equipment in the early hours of the morning. The supplier initially said it would replace damaged equipment but not TVs Fridges etc.

After pressure from residents and a threat of a public meeting backed by the parish council who had collated details of the damaged equipment a spokesman for the supplier in a TV interview last night agreed to replace all damaged equipment.

The Anglers Arms landlord was quoted as having £5000 pounds worth of damaged equipment.

Another lady heard a loud noise and went to investigate to see if she had been burgled. When she went back to her bedroom a TV set was smoking.

Not something to be taken lightly.


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## sallytrafic (Jan 17, 2006)

nicholsong said:


> Frank
> 
> Very interesting. When you write abiut 'meters' and waveform are you only referring to test meters or does the same apply to domestic consumption meters?
> 
> ...


Simple resistance devices like an electric kettle will use more power if the voltage is higher but get to temperature quicker so no net cost to you. ie you get what you pay for. If the voltage is higher the current will also be higher.

Things like a TV or a computer have switch mode power supplies which more or less use the same power over a wide range of input voltages. Higher voltage less current.

With motors it all depends on the type, but many motors draw less current for a higher voltage.

You pay for Watts not actually Volts times Amps. The distinction is made because if the current and voltage are not exactly in phase (power factor not equal to 1) then in an ordinary domestic arrangement you get a percentage of your electricity free. Generators are always rated in kVA rather than kW as they can't tell in advance what sort of load you are going to connect to it.


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