Constant High Mains Voltages At Home

[paul_g_787]

I am just trying to make sure I have done everything in my power so that I can prove it is not me at fault.

As I mentioned earlier - try measuring/logging the voltage between the incoming neutral and a "real" earth from a rod or buried pipe/metalwork. Any significant voltage would be evidence of an upstream neutral fault

That is a good idea! I may try that. The more evidence I can get the better.

[paul_g_787]

I am just trying to make sure I have done everything in my power so that I can prove it is not me at fault.

As I mentioned earlier - try measuring/logging the voltage between the incoming neutral and a "real" earth from a rod or buried pipe/metalwork. Any significant voltage would be evidence of an upstream neutral fault

That is a good idea! I may try that. The more evidence I can get the better.

OK so I took a log of the voltage between a big metal pipe in the ground outside and my neutral from the socket closest to the distribution panel.
Over the course of today it varies randomly every few seconds between 1 and 13V!!! So I think we have found a clue.

When the electrician came round to inspect my meter and it's connections before, I watched him, after he completed his testing, re-connect the output wires from the meter which go to my distribution board, and also he checked the input terminal bolts too. He, in my opinion did this 100% correctly and I am confident that the connections in the meter are good.

I have personally checked that every single connection in my distribution board is done up tight and also in every socket, switch and fused spur in the whole house. So I am 100% that I have no bad neutral (or live or earth for that matter) in the house.

So now I will go to them first thing Monday and badger them as much as possible to try to get an electrical engineer sent out and I am thinking of requesting another volt meter recorder in the meter cabinet.

[Alti]

Over the course of today it varies randomly every few seconds between 1 and 13V!!! So I think we have found a clue.

This is nothing unexpected, that is how TN earthing works.

[gnuarm]

Over the course of today it varies randomly every few seconds between 1 and 13V!!! So I think we have found a clue.

This is nothing unexpected, that is how TN earthing works.

I don't know the standard, but I would think a 13 volt drop in the neutral is excessive.  That's >5% of the total power being dissipated if the load is fully on one phase!  If this high a loss is occurring with a load that is even partly balanced on the three phases that is pretty insane.  No?

[Monkeh]

Over the course of today it varies randomly every few seconds between 1 and 13V!!! So I think we have found a clue.

This is nothing unexpected, that is how TN earthing works.

I don't know the standard, but I would think a 13 volt drop in the neutral is excessive.  That's >5% of the total power being dissipated if the load is fully on one phase!  If this high a loss is occurring with a load that is even partly balanced on the three phases that is pretty insane.  No?

Assuming the ground at the house is at the same potential as the ground at the transformer. The ground not being a superconductor..

Correlation with excessive phase voltage would be more definitive. 13V doesn't sound amazing, though.

[gnuarm]

Over the course of today it varies randomly every few seconds between 1 and 13V!!! So I think we have found a clue.

This is nothing unexpected, that is how TN earthing works.

I don't know the standard, but I would think a 13 volt drop in the neutral is excessive.  That's >5% of the total power being dissipated if the load is fully on one phase!  If this high a loss is occurring with a load that is even partly balanced on the three phases that is pretty insane.  No?

Assuming the ground at the house is at the same potential as the ground at the transformer. The ground not being a superconductor..

Correlation with excessive phase voltage would be more definitive. 13V doesn't sound amazing, though.

I don't get your reasoning.  Even if the impedance between the two grounds is significant, there should be virtually no current, so no voltage drop.  The only way there would be voltage between the grounds is if there were enough current in the neutral to push current through the grounds as well as they are connected to the same points.  So regardless, one way or the other there is excessive impedance in the neutral.  You did notice that he said, "between 1 and 13V", right? 

Consider if the neutral is supporting "between 1 and 13V" that means at some point there is nearly no voltage and nearly no current, then 13 times as much voltage and current.  Yeah, something is messed up and it needs to be fixed.

[Monkeh]

there should be virtually no current

I dare you to test that theory anywhere near train tracks.

[Alti]

Why no current in neutral? There are only single phase loads there and the assumption about balanced load is optimistic. For the purpose of diagnosing a fault you have to consider worst case and accept the fact that whatever amps distribution company sold, can be technically pushed through neutral*. Only then an observation out of bounds indicates a fault.

Additionally, according to IEC 60364-4-43 neutral can be installed with half of the cross section of phase conductor (when some additional requirements are met). I do not know british standards regarding conductor protection but lets assume this is the arrangement that is installed. At full balanced resistive load there is ~0V drop in neutral and 253-207V=46V drop on each phase, this is still not a fault but legitimate practice of setting transformer on last tap when thin cables are installed. Had you switched off load on one phase now, the neutral current is going to equal the disconnected phase current due to Kirchoffs law but the voltage drop in neutral raises to twice the phase drop due to thinner neutral cable. Still this is not unexpected but would result in "Constant High Mains Voltages At Home" topic. So IMHO only after you exceed 253V + 2*46V=345V 253V+46V*sqrt3/2=293V you can look for faults in wiring.

If a neighbor has 6.5V drop on phase conductor and 13V on a neutral conductor, this is not a miracle, just Ohm's law.


*Actually, even IN=3xIL is still not a miracle or a fault, just odd tripplens but lets not overdo with pesimism with this analysis.

[gnuarm]

If a neighbor has 6.5V drop on phase conductor and 13V on a neutral conductor, this is not a miracle, just Ohm's law.


*Actually, even IN=3xIL is still not a miracle or a fault, just odd tripplens but lets not overdo with pesimism with this analysis.

If you see 6.5V drop on the "hot" wire and 13V drop on the neutral, that's >7.5% of the power lost in the conductor.  No utility is going to be so frugal with the conductor as to waste that much power in wiring losses from the transformer to  the home unless the meter is at the transformer.  What you are describing is a fault in the line. 

[Siwastaja]

It is certainly possible to see 7.5% power loss between the distribution transformer and the house.

It's certainly not very common, and definitely not the design goal, but things like this happen for example when the wiring is old and the consumption has increased beyond what was originally considered. New customers, or customers transitioning from gas/oil to electric heating are typical culprits.

Fixing the thing is much more costly than losing 7.5% of the energy, especially if everybody operates on quarter years and not quarter centuries.

The biggest problem isn't the loss itself, but the voltage instability as described.

[Gyro]

The Ze (External Impedance) of our local electricity supply is stated to be "0.35 ohms typical maximum for TNC-S system", our house is 0.1R (measured).

From there you can apply ohms law to get the efficiency.

[Alti]

(..)that's >7.5% of the power lost in the conductor.  No utility is going to be so frugal with the conductor as to waste that much power in wiring losses from the transformer to  the home unless the meter is at the transformer.  What you are describing is a fault in the line.

Your interpretation of "fault in the line" is quite wide.
I must assure you that no efforts in fixing terminations, calling sparkys or even electrical engineers are going to help OP in fixing such "fault in the line". That is because distribution company is well aware of ohms law and the consequences of selling amps beyond reason, switching taps, all without conductor upgrade.

As for being frugal - why would a monopolyst care about electrical energy loss? There is no such term in their dictionary, this just raises distribution costs and they list that on your bill. By definition.

[richard.cs]

Yes, I have suspected that there is an issue that they know about which they are not willing to fix. I live in a small village, well now it is technically a town. They have built several housing estates here over the last 5 years and I suspect that the wiring to our town is just not 'big' enough to cope.

New housing estates of any significant size will have new distribution transformers. If the new estates are to blame then it's a HV problem that will be affecting a wider area.

As I said, a small town, we about 3 miles from the 'big' town.
We have underground distribution.
I am less than 1 mile from the transformer.
I am not sure if it has 2 or 3 HV bushings or of the condition of the transformer as I have never seen it, it is in a small brick out building at the end of the street.
My earthing system is TNCS: so no rod.

1 mile would be a very long way, typically you would expect to be within 200 m or so. In a town, with underground distribution etc. it is almost certainly three phase unless you live in a very old area where ex-DC cables might be 3 core. With TNC-S I would expect UKPN to be very hot on neutral resistance as it is a serious safety issue.

I highly suspect that they are setting the voltage higher to cope for the increased load from the new build estates. Although this is just suspicion and I have nothing to prove this.

This is possible, but that would have to be high voltage on the HV side as they will (probably) not share an LV transformer with you. For reference, the 11 kV HV supply (everyone in the industry calls this MV but the term is deprecated) is quasi-regulated with automatic tap changing at the primary substation. The LV transformers have selectable taps but these can only be changed manually on site and in most cases they are set to 250 V and only changed if there are problems.

OK so I took a log of the voltage between a big metal pipe in the ground outside and my neutral from the socket closest to the distribution panel.
Over the course of today it varies randomly every few seconds between 1 and 13V!!! So I think we have found a clue.

This voltage range is totally normal on TNC-S. What you really need to do is record this voltage when the mains voltage is out of spec (but carefully, because the voltage between your TNC-S earth and the pipe might be large enough to be hazardous). If the voltage to true earth is much higher under that condition then that's strong evidence for a bad neutral between you and the substation. If it's still in this range then the problem lies elsewhere.

If you never see less than 245 V it might be you are very close to the transformer, and they are unwilling to change down a tap because someone else far away would go out of spec at the bottom end. However, the voltages you are seeing are too high to be explained by the transformer being on the 250 V tap, the 315 V for definite, 270 V is stretching plausibility a little. The transformer is normally rated for 5% drop at full load (about 2/3 of this is inductive), so a tap for 250 V at full load would be expected to be no higher than 263 V with zero load. I mean maybe, if there's almost no load on your phase so that would be 263 V, and heavy load on the other phases pulling the neutral away from you, that could get to 270 V, but the 315 V can only be a fault.

In any case UKPN are in breach of their statutory obligations once it goes beyond 253 V and inaction after clear evidence surprises me somewhat.

[Siwastaja]

As for being frugal - why would a monopolyst care about electrical energy loss? There is no such term in their dictionary, this just raises distribution costs and they list that on your bill. By definition.

This. Even if the meter is on the customer's house and hence the wasted energy isn't billed directly, it's the customer who eventually pays for the whole shebang.

[gnuarm]

As for being frugal - why would a monopolyst care about electrical energy loss? There is no such term in their dictionary, this just raises distribution costs and they list that on your bill. By definition.

This. Even if the meter is on the customer's house and hence the wasted energy isn't billed directly, it's the customer who eventually pays for the whole shebang.

I don't know how they are managed in the UK, but in the US utilities are required to get their rates approved.  That only happens every so often so in the mean time the way to higher profits are to reduce costs.  Wasted power in distribution is a cost.  So like nearly every company, costs and waste are minimized. 

What utilities are not encouraged to do is minimize capital investment.  In fact, the profits are often normalized to capital investment, so greater investment allows higher profits at rate setting time. 

[paul_g_787]

Hi. Thanks for getting back to me.

Yes, I have suspected that there is an issue that they know about which they are not willing to fix. I live in a small village, well now it is technically a town. They have built several housing estates here over the last 5 years and I suspect that the wiring to our town is just not 'big' enough to cope.

New housing estates of any significant size will have new distribution transformers. If the new estates are to blame then it's a HV problem that will be affecting a wider area.

My street was built in 1995 at the time time the transformer was fitted. There are a fair few transformers in this 'older' part of the estate but in the new areas I have yet to find and transformers. Unless they are underground I think they are just tapping off the existing ones.

As I said, a small town, we about 3 miles from the 'big' town.
We have underground distribution.
I am less than 1 mile from the transformer.
I am not sure if it has 2 or 3 HV bushings or of the condition of the transformer as I have never seen it, it is in a small brick out building at the end of the street.
My earthing system is TNCS: so no rod.

1 mile would be a very long way, typically you would expect to be within 200 m or so. In a town, with underground distribution etc. it is almost certainly three phase unless you live in a very old area where ex-DC cables might be 3 core. With TNC-S I would expect UKPN to be very hot on neutral resistance as it is a serious safety issue.

I would gues it is around 200m. It is literally at the entranc eto our cul-de-sac and there is about 12 house on my side of the street between me and the transformer. The UKPN electrician said I am the last house on this phase.

I have already highlighted this as a safety issue to them on the phone and they just threaten to come and cut off my electricity immediately and will not forward my call further.

I highly suspect that they are setting the voltage higher to cope for the increased load from the new build estates. Although this is just suspicion and I have nothing to prove this.

This is possible, but that would have to be high voltage on the HV side as they will (probably) not share an LV transformer with you. For reference, the 11 kV HV supply (everyone in the industry calls this MV but the term is deprecated) is quasi-regulated with automatic tap changing at the primary substation. The LV transformers have selectable taps but these can only be changed manually on site and in most cases they are set to 250 V and only changed if there are problems.

The UKPN electrician said our tap is set to 249V at the transformer.

OK so I took a log of the voltage between a big metal pipe in the ground outside and my neutral from the socket closest to the distribution panel.
Over the course of today it varies randomly every few seconds between 1 and 13V!!! So I think we have found a clue.

This voltage range is totally normal on TNC-S. What you really need to do is record this voltage when the mains voltage is out of spec (but carefully, because the voltage between your TNC-S earth and the pipe might be large enough to be hazardous). If the voltage to true earth is much higher under that condition then that's strong evidence for a bad neutral between you and the substation. If it's still in this range then the problem lies elsewhere.
Surely this would have shown in their readings?

The 1-13V reading is between the 'real earth' and neutral. I am not getting these readings between the plug socket earth and neutral. It is always less than 0.1V there.

If you never see less than 245 V it might be you are very close to the transformer, and they are unwilling to change down a tap because someone else far away would go out of spec at the bottom end. However, the voltages you are seeing are too high to be explained by the transformer being on the 250 V tap, the 315 V for definite, 270 V is stretching plausibility a little. The transformer is normally rated for 5% drop at full load (about 2/3 of this is inductive), so a tap for 250 V at full load would be expected to be no higher than 263 V with zero load. I mean maybe, if there's almost no load on your phase so that would be 263 V, and heavy load on the other phases pulling the neutral away from you, that could get to 270 V, but the 315 V can only be a fault.

In any case UKPN are in breach of their statutory obligations once it goes beyond 253 V and inaction after clear evidence surprises me somewhat.

Again they said I am the last house on this phase, so surely this would mean all the nearer houses are getting higher voltages than me and I am the highest.

Went for a walk today and 2 of my neighbours further up the road have old fridges on the pavement. I expect blown up from the high voltage.

Often at night, usually about 1-3am (it varies exactly when) the mains voltage will jump suddenly from around 255 to approx 262V for around 5-20 minutes, then suddenly drop down again to around 254/255V. But never in the daytime, today it has been 246 - 252 so far (now 3pm). Some nights it doesn't do it, but I would say around 85% of the time it does.

[paul_g_787]

I have found a copy of the voltage readings from when I first reported the issue. These were the readings UKPN sent me after they removed their volt meter from the cabinet. I have not heard from them since!

Also attached is the letter I received.

I have redacted personal details if you are wondering about the big black smudges

[Monkeh]

I have already highlighted this as a safety issue to them on the phone and they just threaten to come and cut off my electricity immediately and will not forward my call further.

They can't do that.

Report this behaviour along with copies of the letter and plots given to you by UKPN to the Energy Ombudsman: https://www.ombudsman-services.org/

E: It seems UKPN don't deal with the Ombudsman. They're also Chinese owned, this somehow doesn't surprise me. I would still give the Ombudsman a call, if they can't help you, call Citizens Advice, if they can't, call Ofgem. Normally Ofgem don't get involved in consumer disputes but they're the last port of call and ultimate authority.

[Alti]

Again they said I am the last house on this phase, so surely this would mean all the nearer houses are getting higher voltages than me and I am the highest.

It seems you do not understand three phase supply.
Since you are the last one, you are going to experience the highest voltage across neutral (or should I say PEN as this is TN-C-S). This neutral voltage might come from the load on:
- only your-phase (you experience voltage drop in socket) or
- only not-your-phases (you experience voltage raise in socket)
- or some other combination of loads where the end result is more convoluted.

The point here is that neutral is shared between all of your neighbours. Had you been connected next to transformer, there would have been no problems with overvoltage. IMHO.

[richard.cs]

Their voltage readings are much lower than the worst case you've observed, but still clearly out of spec. I wouldn't bother phoning them, it's pretty useless, and I wouldn't accept any phone calls either, insist on having everything in writing.

I would write directly to the Supply Quality Manager whose name and address you have, reference the letter, their previous acceptance that the supply is out of tolerance, your continued problems, etc. Give them a reasonable but clear deadline, say 4 weeks, and state that you will be in contact with the ombudsman if you don't receive a reasonable response in that timeframe. They will probably ignore it or send you some standard template letter, but that's fine, this is all good evidence. A recent letter and evidence of recent inaction will be helpful in getting the ombudsman on side.

Unfortunately the ombudsman is probably more used to dealing with complaints about money, payment to metering operators, etc. and may not be too familiar with technical supply-quality complaints. Still your best route though.

Again they said I am the last house on this phase, so surely this would mean all the nearer houses are getting higher voltages than me and I am the highest.

It seems you do not understand three phase supply.
Since you are the last one, you are going to experience the highest voltage across neutral (or should I say PEN as this is TN-C-S). This neutral voltage might come from the load on:
- only your-phase (you experience voltage drop in socket) or
- only not-your-phases (you experience voltage raise in socket)
- or some other combination of loads where the end result is more convoluted.

The point here is that neutral is shared between all of your neighbours. Had you been connected next to transformer, there would have been no problems with overvoltage. IMHO.

Put another way, being far away is bad because both line and neutral voltage are more variable and with the particular combinations of loads on your street this variation results in your seeing high voltages. Typically, your line voltage may be lower than near the transformer (relative to N at the substation) but almost certainly your neutral voltage is a long way from zero (again relative to the substation N). In your case the neutral voltage is perhaps a few tens of Volts, but opposite in phase to your line voltage because the neutral is being pulled away from zero by loads on other phases, that increases the L-N voltage you observe.

The most recent information you've given suggests that you probably have a full-sized neutral (based on the date) but that your phase is very lightly loaded whilst the others are heavily loaded at night and without any large loads on your phase this results in the long, relatively high resistance neutral being pulled away from your phase towards the other two. Maybe there's simply an unlucky combination of loads and it just happens that most of the houses on your phase are unoccupied, gas-heated, etc. and most of the houses on the other two phases are heavy night-time users with storage heaters. Statistically this has to happen occasionally. Or maybe the cable jointers screwed up and you are the only house on your phase.

It would be possible to make some further measurements that might help confirm what's happening, but it's not especially useful, it's UKPN's problem to fix.

[f4eru]

seeing the drop on your voltage is a few volt when consuming 20A, that looks like a pretty normal source impedance here.

[gnuarm]

seeing the drop on your voltage is a few volt when consuming 20A, that looks like a pretty normal source impedance here.

I'm not sure what voltages you are saying are ok.  I've measured the voltages at my house when the water heater was drawing about 18 amps and it was still spot on.  The run to the transformer is not far of course.  I guess that's the part I don't get, the use of such long runs of low voltage cables.  In the US they typically limit the runs to a few hundred feet (approx 100 m) other than seriously rural runs that were put in 50 years ago. 

[f4eru]

The (very small) drop of voltage when suddently switching on 20A of load gives a hint on the short term source impedance.
Here it seems OK, so as a consequence, the neutral seems not to have a high impedance in itself -> no loose connection close by.

[richard.cs]

In the US they typically limit the runs to a few hundred feet (approx 100 m) other than seriously rural runs that were put in 50 years ago.

This is consistent, most US installs would be split phase so around 240 V L-L, UK installs would be 3 phase over most of that distance so 400 V L-L, the voltage is sqrt(3) higher, the impedance is 3x higher, so you can go 3x the distance for the same power loss.

A very typical suburban setup in the UK would be a 500 kVA, three-phase, delta-star transformer from 11 kV to 400 V, feeding perhaps ten outgoing three-phase cables fused at around ~400 A, each with numerous branches to feed single or three phase customers. There would usually be linkboxes under the pavement allowing interconnection of different LV cables from the same or different substations. This is quite different from the usual US approach with numerous small transformers.

[gnuarm]

In the US they typically limit the runs to a few hundred feet (approx 100 m) other than seriously rural runs that were put in 50 years ago.

This is consistent, most US installs would be split phase so around 240 V L-L, UK installs would be 3 phase over most of that distance so 400 V L-L, the voltage is sqrt(3) higher, the impedance is 3x higher, so you can go 3x the distance for the same power loss.

A very typical suburban setup in the UK would be a 500 kVA, three-phase, delta-star transformer from 11 kV to 400 V, feeding perhaps ten outgoing three-phase cables fused at around ~400 A, each with numerous branches to feed single or three phase customers. There would usually be linkboxes under the pavement allowing interconnection of different LV cables from the same or different substations. This is quite different from the usual US approach with numerous small transformers.

Your analysis seems to be mistaken.  You are claiming the UK line voltage is higher so the current is smaller, etc, but your math is faulty.  The power to any one home is not three phase, it is one leg to the neutral.  So the current drawn for a given load is the same ~240V as in the US.  The voltage between the phases is irrelevant for the feed from the transformer to the home.  You seem to be talking about the higher voltage lines which are three phase in the US as well.