Voltages spikes on my mains power exceeding 253 volts

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  • thebatfink's Avatar
    Level 3

    I couldn’t see anything previously posted via a search so perhaps an odd issue? But I experience momentary spikes on my mains power of over 253v. I have some electrical devices which are powering off due to over volt protection when voltage exceeds 253v for more than 5 seconds. I validated the voltage in my home using three brands of devices, two power monitoring devices inserted into my mains wall sockets and a third clamped around the incoming mains cabling to my consumer box. Whilst these devices are obviously not professional grade devices a mains electricity technician would likely use, all three log the voltage and all three see the same spikes at the same time - and obviously a 4th is powering itself off due to protection features so I have some confidence something is amiss somewhere..

    It happens intermittently but usually I see this once or twice per day and I have recordings of the voltage hitting 255v. It is on average over 245v. Here is a chart of my incoming mains voltage from yesterday / this morning. Just yesterday there were two excursions above 253v. https://imgur.com/a/Mevkieq this occured whilst the house is empty in the day. I have seen them sometimes at 1am in the morning. Here is the past week, whilst the volume of data makes it difficult to see finely on a chart of this size, almost every day there is a clear excursion to and above 253v https://imgur.com/a/0kiQb8x I feel like this started happening in the last few weeks.

    I am not an expert in such things, but google would have me believe the quoted upper tolerance voltage of UK mains should be 253v and it is now causing me problems. How would one even go about getting something like this looked at?

    Last edited by thebatfink; 11-04-24 at 06:03.
  • 8 Replies

  • Best Answer

    retrotecchie's Avatar
    Level 92
    Best Answer

    Up until we harmonised with Europe several years ago, the 'nominal' supply voltage was 240v here in the UK.

    After harmonisation, the whole of Europe 'standardised' on a nominal 230v as the pan-European domestic supply voltage.

    The IEEE state this:

    For many years the supply voltage for single-phase supplies in the UK has been 240V +/- 6%, giving a possible spread of voltage from 226V to 254 V. For three-phase supplies the voltage was 415 V +/- 6%, the spread being from 390 V to 440V. Most continental voltage levels have been 220/380V.
    In 1988 an agreement was reached that voltage levels across Europe should be unified at 230V single phase and 400V three-phase with effect from January 1st, 1995. In both cases the tolerance levels have become -6% to +10%, giving a single-phase voltage spread of 216 V to 253 V, with three-phase values between 376V and 440 V. It is proposed that on January 1st, 2003 the tolerance levels will be widened to +/- 10%.

    So with 230v as the nominal voltage, and the new tolerance levels of +/- 10% which were duly accepted by the energy industry, your mains supply voltage is allowed to be anywhere between a minimum of 207v and a maximum of 253v.

    Much of the UK supply is still at around 240v nominal, and a tolerance of +/- 10%, then 206v to 264v is still allowable.

    Most switch-mode power supplies are happy with a supply voltage of up to 275v with no problems at all.

    What matters more than the voltage variation is the frequency variation. The nominal mains frequency is 50Hz. According to National Grid:

    National Grid is obliged by its licence commitments to control the frequency within ±1% of 50Hz so it can fluctuate between 49.5Hz to 50.5Hz. However the normal operational limits are 49.8Hz to 50.2Hz.
    Don't shoot me, I'm only the piano player. I DON'T work for or on behalf of EON.Next, but am willing to try and help if I can. Not on mains gas, mobile network or mains drainage. House heated almost entirely by baby dragons.
  • meldrewreborn's Avatar
    Level 91
    one for @retrotecchie I Think. I’d guess you need to report this to your local DNO, but I’m not an expert in this stuff.
    Current Eon Next customer, ex EDF, Zog and Symbio. Don't think dual fuel saves money and don't like smart meters. Chronologically Gifted. If I offend let me know by private message, but I’ll continue to express my opinions nonetheless.
  • retrotecchie's Avatar
    Level 92

    Yes, as my learned colleague says, a phone call to the DNO would be in order. Do you live near to a large commercial operation or perhaps at the very end of a rural supply, as overvoltage is almost always caused by something on the same supply line turning off a very heavy load. In my case it's either just after milking time at the farm next door or when the local food factory changes shift at 7am and 7pm. I regularly get spikes of 255v or more but they won't often do any real harm, but the 'brownouts' where the supply very briefly drops below 220v are more noticeable, especially at night. That said, my house (c. 1840 build) at the end of a very long overhead rural 11kv line is protected by a surge protector/MOV in the consumer unit. 18th Edition regs insist on this for new builds or rewires but are always a good retrofit if you have supply issues.

  • thebatfink's Avatar
    Level 3
    Not rural no. Looks like it is nationalgrid?

    They arent doing harm. Just these couple of devices I brought that have firmware hardcoded with over volt protection so that they shut off @ > 253v if the excursion lasts longer than 4 seconds.

    I also enquired with this vendor if they’ll change the firmware but I imagine they’ll have no interest in doing so. Its this shut off thats my issue.

    I found this webpage https://www.spenergynetworks.co.uk/p...253.0%20volts. which states it should be between 216 and 253 which is why (I presume and assuming that tolerance range is correct) the device manufacturer applied the >4 seconds @ >253v logic into the device.
    Last edited by thebatfink; 11-04-24 at 14:17.
  • wizzo227's Avatar
    Level 21
    My Distribution Network Operator (DNO) are Scottish and Southern Electricity (SSE), as found from the gate badge on the front of your nearest street transformer. From a similar query a few years back they fitted their measuring device next to my meter and concluded no problem. It is supposed to be the DNO who decide that.

    Your chart shows a bit higher than mine here in Oxfordshire, particularly in the daytime and particularly those spikes which tripped you. Somebody should find out what caused those spikes and I'd have thought that the DNO should if the cause of them was outside of your premises. I'm surprised at your equipment tripping so easily. I've had higher rms here on occasion without problem. Many 21st century appliances are supposed to tolerate 265 Volts rms and have inside a switched mode power supply which downconverts to what the stuff inside really needs. Those don't care whether they get 200 Volts or 260; they just change the switched pattern a bit to get what they need. Straight 50Hz transformers 1960's style are less common. So a firmware or setting tweak on your device might be ok, but how to get that from the manufactuer is another matter. What sort of machine is it ?

    You are correct that UK mains is supposed to stay inside 216 to 253 Volts rms at all times.
    Mine typically looks like 242 to 246 Volts at night time, decreasing to about 232 to 236 Volts for a few hours of peak use of the street around tea time.
    I measured that the waveform shape here is always more trapezoidal than pure sinewave, getting a measured peak:rms ratio of always 1.37 to 1.38 instead of the 1.414141... expected for ideal sinewaves. Do you have any idea of what caused those nasty looking spikes? For example could they be bigger and shorter duration than shows up on your rms chart ?
  • DebF_EONNext's Avatar
    Community Team
    Hey @thebatfink it's great to see you on the community again, welcome back 😊 Can I just say this thread has absolutely blown my mind 🤯 it's very tecchy and way above my head, so I am glad you have these 3 musketeers @meldrewreborn @retrotecchie and @wizzo227 around for support (you lot are fantastic!).

    If anyone would like to explain this in simpler terms for me that would be amazing as I would love to get my geek on and learn more 🤓
    Last edited by DebF_EONNext; 13-04-24 at 09:58.
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  • meldrewreborn's Avatar
    Level 91

    I think I can explain it in simpler terms. If you content yourself with the fact that voltage and frequency can vary between the parameters as detailed by @retrotechie you'll not go far wrong.

    Voltage variations would make things cook faster or slower, while frequency variations would cause a record player disk to revolve faster or slower. I'm afraid my monitoring doesn't extend that far.
  • retrotecchie's Avatar
    Level 92

    Spikes are slightly different to the normal voltage variations. They are usually fairly transient and are most often caused by large inductive loads (motors or high power factor items) being switched on or off.

    Do you have any pattern to these spikes or do they appear totally random? Do they happen at certain times of day or when you use any particular appliances? In a flat I once lived in, my neighbour's oil filled radiator cycling on the thermostat used to make the lights flicker. That's usually a sign of substandard wiring, but quite a few folk I know have had spike issues caused by all sorts of random things.

    If your equipment is that sensitive to spikes, you could always invest in a constant voltage transformer (CVT) to sort the problem out. Depending on the load of course and whether the kit is always on the same socket/ circuit or is something portable. I used to work on some pretty sensitive electronics back in the day and the power on our row of industrial units was far from clean. A Galatrek CVT installed on my bench supply worked a charm.

    Failing that, a suitably rated metal oxide varistor (MOV) would likely protect the equipment itself from spikes.