Electricity Meter spinning disc & Meter "creep"

[IsleofWightPete]

For historic reasons that predate our occupation of our house, our garage has its own separate electricity supply.
Even though there is a games room over, we use very little electricity - electric door openers, few power tools, occasional lights, and looking at the bill I was a little puzzled that we seem to get through about 35 kWh per month - not a lot, but more than i would have thought.

So I decided to check there wasn't some "erroneous" consumption by turning things off at the consumer unit. I discovered a light had been left on in the wc, but it was low energy, and probably hadn't been on for long, so not the issue.

Then I noticed that when EVERYTHING had been turned off, the meter disc was still creeping round. Not much, but definitely moving even with the CU master switches turned off. I calculated it is moving at a rate of one turn every 6 minutes.

So two questions:
1) Does anyone know how much electricity consumption is represented by one turn of the spinning disc? The main display shows consumption down to 1/10th of a unit, so might the disc be one revolution per 100th of a unit? That would imply one turn per 6 minutes is 240 turns per day or 2.4 units per day, but that would be more than the ~1 unit a day we are actually using. So maybe it is 1000th of a unit?

2) Meter "creep" seems to be a known effect, but I can't find out what is acceptable and what is excessive. Does anyone know that?

TIA

[csearle]

So two questions:
1) Does anyone know how much electricity consumption is represented by one turn of the spinning disc? The main display shows consumption down to 1/10th of a unit, so might the disc be one revolution per 100th of a unit? That would imply one turn per 6 minutes is 240 turns per day or 2.4 units per day, but that would be more than the ~1 unit a day we are actually using. So maybe it is 1000th of a unit?

2) Meter "creep" seems to be a known effect, but I can't find out what is acceptable and what is excessive. Does anyone know that?

My meter has the writing 1662/3 rev/kWh written next to the disc. Does yours not have something similar?

I think your disc should be absolutely still if no current is flowing. Not sure about the creep you mention but all the meters I have ever had/seen have remained stationary when the main switch is off. I think you have a circuit somewhere that is still connected.

Chris

[IsleofWightPete]

My meter has the writing 1662/3 rev/kWh written next to the disc. Does yours not have something similar?

By jove, it does! Not written close to the disc, but I still don't know how I missed that!
Mine says 200 revs per kWh, so my estimated 6 mins per revolution = 10 revs per hour = 240 revs per day = 1.2 kWh per day, or damn near our entire consumption! (I'll check it again tomorrow when it isn't a) dark and b) so damn cold!).
But if my measurement and my maths are both correct, this isn't some tiny leakage, this is actually running at 50w. Is that right?

I think your disc should be absolutely still if no current is flowing. Not sure about the creep you mention but all the meters I have ever had/seen have remained stationary when the main switch is off. I think you have a circuit somewhere that is still connected.
Chris

Hmmmm, I can't see how there can be a circuit connected, as the tails clearly come out of the meter and straight into the CU, and as far as I know it isn't possible to wire anything to the "wrong" (supply) side of the master switch on the CU? (I haven't actually opened the CU to check, though). And I can't see that anything should be drawing a current when the master switch is turned off. Are you aware of any other way that there could be leakage?

I did find this:
https://www.gov.uk/government/uploads/s ... 3-2014.pdf
which suggest acceptable tolerances are +2.5% to -3.5%. But as these are percentages, it implies that under no load, the error should be zero, so no creep allowable at all.

[csearle]

But if my measurement and my maths are both correct, this isn't some tiny leakage, this is actually running at 50w. Is that right?

Sounds right to me.

Hmmmm, I can't see how there can be a circuit connected, as the tails clearly come out of the meter and straight into the CU, and as far as I know it isn't possible to wire anything to the "wrong" (supply) side of the master switch on the CU? (I haven't actually opened the CU to check, though). And I can't see that anything should be drawing a current when the master switch is turned off. Are you aware of any other way that there could be leakage?

It is possible to wire things to the wrong side of the main switch. It should not normally* be done though. But in your case I think it possibly has been. If I were you I'd switch off, unscrew the lid, and check.

I wonder if perhaps you have another CU connected directly to the meter (via the CU) or perhaps a doorbell transformer or similar.

Chris
* Were there to have been an isolation switch between your meter and your CU then it would be in accordance with the Wiring Regs to connect another CU in parallel from the input of the CU's main switch.

[quelquod]

Now that would really be a lossy transformer!

[Lootman]

I think your disc should be absolutely still if no current is flowing. Not sure about the creep you mention but all the meters I have ever had/seen have remained stationary when the main switch is off. I think you have a circuit somewhere that is still connected.

Could there be some kind of short circuit, perhaps a leakage to ground/earth?

Or could there be recharging of a capacitor somewhere in the system?

Old wiring buried in a wall that dissipates charge through heat?

I don't know about creep but I've noticed the same thing. If I turn off the power, the wheel stops. But if I instead just turn off all the devices and appliances, the wheel still turns slowly.

Back at Uni I shared a flat with a physics undergrad and he rigged something up with magnets that would make the wheel stop. It was read quarterly and so we would go "forward" for one month out of three. We were never discovered.

[csearle]

Now that would really be a lossy transformer!

I was clutching at straws!

[quelquod]

Back at Uni I shared a flat with a physics undergrad and he rigged something up with magnets that would make the wheel stop. It was read quarterly and so we would go "forward" for one month out of three. We were never discovered.

That really astonishes me.

In the dim and distant past I did some work for GEC Meters (Stone) who at the time were the largest UK meter manufacturer. They demonstrated that the meter maintained its accuracy at field levels that realistically couldn't be achieved outside of a laboratory setup. I've not checked, but I doubt if modern meters are worse in this respect.

When I was a penniless undergrad the standard technique was to push a needle through the seal, slide the tie along and undo it, then disconnect the voltage coil to stop the meter. How would I know?

[bungeejumper]

I've heard of the magnet trick, but that was getting on for fifty years ago. I think you needed a powerful electromagnet to make it work - but then, how else could you afford the electricity needed to run it? Can't imagine that any remotely recent meters would be susceptible.

IoWP, you implied (I think) that the garage hadn't always belonged with your property. I don't suppose there's somebody on the other side of the wall who's still running a light off your circuit? (An outside wall light maybe?) But yes, it's possible to tap into mains supplies beyond the meter if you're skilled/stupid enough to do it. Domestic cannabis farmers couldn't make an honest living any other way.

BJ

[woolly]

You don't have solar panels connected by any chance? If there is nothing else switched on the wheel will spin backwards when the PV installation is generating...

[IsleofWightPete]

Curiouser and curiouser.

I have dome some more checking, and today, when I turn off the main consumer unit switch, the disc does stop dead. It definitely did NOT do that yesterday.

I have opened the CU. There is nothing live in there when the CU master switch is off, except the incoming tail, as you would expect. There is nothing connected direct to the tails on the supply side of the master switch. I can clearly see the tails from the meter to the CU, and nothing could be connected anywhere in that part, so no dodgy abstraction anywhere, and certainly not between the meter and CU.

The system was completely rewired by Southern Electric in mid 90's, when we bought the place, and a new replacement CU was installed when we built an adjacent additional garage to provide extra ways to supply power to lights & sockets in there. I can clearly see where that cable is fed from one of the ways in the main CU, so it is not bypassing the master switch. That anyway was installed by a competent electrician, and no one could possibly have tampered with it since.

There is no Solar or similar.

So now we seem to have an intermittent dodgy meter?????
Great! There's only one thing worse than a dodgy meter, and that is, of course, and intermittently dodgy one, because you can be sure it won't be dodgy when you need to demonstrate it to someone!!

[csearle]

So now we seem to have an intermittent dodgy meter?????

Crikey. That sounds unlikely. Just as unlikely is the possibility that you have a dodgy main switch in the CU, such that is doesn't always switch off. But if I've understood you correctly, as the disc unexpectedly rotated, you not only had the mains switch switched off but all of the MCBs too. I don't understand it, unless the tails are damaged in some way? Neutral tail touching Earth and causing a small current to flow? Unlikely as the tails are obviously double insulated.

Might be worth exercising the main switch and seeing if it appears to be reliably turning the power off? I'm running out of ideas!

Chris

[bungeejumper]

Only the other day, a friend was telling me about an old schoolfriend who could stop any electrical device just by being near it. Cookers, computers, clocks, boilers, televisions. His usual response when it happened was to turn his head over his shoulder and say, "stop that, granddad". Whereupon, on at least one occasion witnessed by my friend, it did.

A garage, you say? You've seen Poltergeist, I take it?

BJ

[IsleofWightPete]

the possibility that you have a dodgy main switch in the CU, such that is doesn't always switch off. But if I've understood you correctly, as the disc unexpectedly rotated, you not only had the mains switch switched off but all of the MCBs too.

Yup, that's right..... mind you, I am beginning to doubt myself, so will definitely double check that if i catch the meter at it again.

I don't understand it, unless the tails are damaged in some way? Neutral tail touching Earth and causing a small current to flow? Unlikely as the tails are obviously double insulated.

Might be worth exercising the main switch and seeing if it appears to be reliably turning the power off? I'm running out of ideas!

Chris

Tails definitely not damaged and no stray strands (not that the strands in the tails are anywhere near flexible enough or thin enough to curl out without it being obvious, but nothing from any of the other lighter weight wires anywhere near).

I'll certainly jiggle the switch a bit and check that - as you say, it is the only other thing remaining, IF i had left one of the MCB's on when i operated the master switch.

[IsleofWightPete]

I've just been out there again.
Shut off every MCB & RCD, but left master switch on - disc still turning slowly.
I then turned off master switch - disc still turning slowly.
Took video of all switches in off position and disc moving to reassure myself I am not barking mad.

Then played with master switches & mcb's and rcd's on and off a few times in different combinations, then turned all off. Disc then stopped dead with everything off. I then thought it MUST be a dodgy Master switch, AND some internal leakage in the CU. But switching ON the master switch again, (with all the MCB's and RCD's still off) didn't start the disc spinning. So any mysterious leakage through one of the MCB's/RCD's had suddenly vanished ???? I can't believe there are two intermittent failures on both the master switch AND something else.

I just don't get it.

And incidentally, the rate of rotation, when it was still spinning with everything off, was much slower today than yesterday - a rate of 1 rev every 26 minutes or so, rather than yesterday at 1 rev per about 6 mins.

I guess the fault must lie in the meter somehow, it is too long a shot that it could be two separate intermittent faults in the CU combining, but can't work out how different combinations of "off" in the CU could make the meter start and stop, either.

[csearle]

Took video of all switches in off position and disc moving to reassure myself I am not barking mad.

Ok, Pete, glad we've ruled that out.

I can't believe there are two intermittent failures on both the master switch AND something else.

Yes the already small probabilities multiply toward the infinitesimal.

I just don't get it.

Neither do I

I guess the fault must lie in the meter somehow...

I'm begining to agree with you. Have you tried hitting it? No, seriously, when it rotates inexplicably try subjecting the meter to a little bit of, er, sudden mechanical stress to see if this affects the disc rotation. Obviously it shouldn't, but if it does, then that might help support your defective meter hypothesis.

In the meantime I'm going to see if I can get some help from a more experienced electrician.

Cheers,
Chris

[jfgw]

I happened upon this which, while American, should be largely relevant,

https://www.usbr.gov/power/data/fist/fi ... ol3-10.pdf .

The maximum creep specified in this (American) reference is one revolution every 10 minutes. Th number of revolutions per kWh is not taken into consideration.

From page 5 (pdf page 12),

3.4.
FRICTION.
To compensate for friction, additional torque must be in­troduced. This usually is accomplished by placing a movable short-circuited turn of large cross section in part of the field of the voltage (potential) coil. This also serves as a "light-load" adjustment.

6.3 (page 23 (pdf page 30)) lists a number of sources of error. Some (such as dirt) could be intermittent. I suspect that it is possible for gummy oil to have a variable effect dependent upon temperature.

8.3 (pages 32,33 (pdf pages 39,40)) state:

Meter disks usually have holes or slots punched in them to stop creep when the holes or slots reach a position directly under the potential coil pole. Observation of creep should, therefore, be based upon at least one complete revolution.

Julian F. G. W.

[csearle]

Clearly you are not the only poor soul to suffer from this problem. This is another such unfortunate. I wouldn't bother reading it all though as I did as they haven't really mentioned anything different to us.

Interesting that this creep can happen without a load though! Maybe it's a "simple" as that?

Chris

[dspp]

If the meter is indeed duff, which it is increasingly sounding as if it is, then your evidence should get the DNO / meter supplier out fairly quickly to replace it with a new meter. The main problem will be arguing the toss about when it went duff.

As the linked Whirlpool Aus forum said the next thing to do is to tong test it. Put a current clamp on one phase wire going into the meter. What does it say ? Interpreting this will be awkward as we do not know the possible failure modes for the meter but at least it will be a tad more info.

regards, dspp

[IsleofWightPete]

Thanks for all the considered input, and the time spent helping me puzzle this out.

I don't have a clamp meter so can't do that final test, and although I normally seize opportunities to add to my tool collection, I think on this occasion, I'll pass on that one (must be getting old!)

I have emailed the supply company, including the video of the meter spinning and a slow pan shot showing every switch in off position, so we will see what they come back with.

I have certainly added to my knowledge a lot from this thread, but have probably spent rather too much time on this problem (and too much of your time probably!).

But I will keep you posted on any developments.

Thanks again to the (Lemon) Fool community! It is great to be able to share perplexing things like this, and do some systematic logic checks and analysis.