I've heard stories about people having old kWh meters and have eiter lower/higher bills than they should. I can understand how an old meter will show up short on kWh, my question is, how can the meter "overcharge" you.... with the parts inside moving faster

Josh,
A kWh meter is a pretty simple sort of a thing, using only a Current (Series) coil and a Voltage (Parallel) coil to excite an Aluminium disc, in the crude form of a motor.
The only real thing that will cause an upset is a shorted winding or two, in the Voltage coil.
It can happen, but very rarely.
What's the problem you have?.

Take a look at this link, which describes how meters work and how to test them.
http://www.utec.com/PDF/Bul_102.PDF

A meter has two coils: the current and the voltage coil. Each of these produces magnetic flux proportional to the respective component, and the composite flux produces _torque_ on the meter disk, proportional to the power flow. This torque would tend to accelerate the meter disk. In order to make the _speed_ of the meter disk proportional to power, some drag is added. The torque reacts against the drag, and you get speed, which you then measure.

If something happened to the drag magnets, the meter would run much more quickly than it should.

-Jon

It is important to note that meters are not "true RMS" meters. What this means is that anything that affects the waveform can result in the meter reading incorrectly- usually "fast."
An example of this is "power factor." If the power factor of a load is low, then the meter will register more watts than are actually used. Correct with capacitors, and the power bill goes down!

Most things that can go wrong with a meter will cause them to read "low." Some customers have been known to do all sorts of things in the area around the meter to effect a lower reading. (I won't give examples, as I'm not running a class for cheats).

winnie:

Great link! A must-read for anyone curious about watthour meters.

Here's another site with lots of meter pics and info:
http://www.themeterguy.com/

Some interesting installations and photos of amazing things related to meters. The site also has photos of portective apparel after a meter bank explosion.

[This message has been edited by mxslick (edited 08-06-2005).]

I have worked 12+ years in on site meter testing, calibration of electromechanical kWh meters and electronic ones.

Running fast, not often but is due to the weakening of the brake magnet. Around 1998 we still took out in Devonport, Auckland NZ, Ferranti FDb meters and Chamberlain & Hookham 10 Amps LR meters which were last tested in 1926. These had an average error of around 7 % at 10 Amps Inom. Considering the normal peak house loads of 40 to 60 Amps + @ 230 Volts the meter would be on overload anyway and the current coil in saturation with a meter error of - 20%. I have proven that on a test bench.

A lot of current coils had shorted turns where the varnish and insulation had burnt of and the metal cased meter was live at mains potential.

On older meters the weakening of the brake magnet and the wearing out of the rotor bearings tend to cancel out each other a little.

The Floton bearing meters 1970's ( Sangamo series ) did not have any major problems at all except Jamming jumping dials.

Most meters up to 50 years old are in general very accurate and overall errors are well wirhin the ±2½ % margin.

Some electronic meters do run fast, we had certain batches of meters around 1994 with capacitors on the circuitboards going faulty and the meter taking off. errors of 600% were found. This affected 1Ø and 3Ø meters. It was quite visible on the meterdial that the meter had a problem with hardly any load the led was blinking like crazy and the numbers of the dial rolling over. :

There was one that made the paper a few years back here in Windsor Ontario Canada.Apparently a family purchased an abandoned house that had outrages electrical bills.They complained to the poco for a few months but like everyone already said it's very rare for a meter to fail like this so they didn't believe him.Before they could come test the meter the special tactical unit showed up and kicked his door in looking for a grow op.Turns out a contract meter reader had turned them in.The write up in the paper said he forgot to lock the door before going to bed so he woke up staring up the barrels of quite a few automatic weapons and a bedroom full of cops in full assault gear.Can you imagine!They also said the poco was inundated with calls to check meters and that for a meter to fail like this is extremely rare.LOL

As noted, meters can run fast, although it is rare compared to how many run slow.

The braking magnet can be weakened by lightning hits. The worst I saw was 30% fast...but the lightning also fried everything in the house as well. The newer (>40 years old) alnico magnets are hard to mess up and the electromechanical meter is one of the most dependable, accurate mass produced products there is.

Considering bearing failure, register drag, debris on the disk, fire ants, fire ants, FIRE ANTS and (did I mention??) fire ants, there are lots more reasons for it to run slow. So look for a reason for the high bills BEFORE you call the POCO, because if the meter turns out to be slow, they WILL speed it up.

Can't comment yet on the electronic ones. They don't have that much of a track record yet in my neck of the woods.

Qoute:
"If the power factor of a load is low, then the meter will register more watts than are actually used. Correct with capacitors, and the power bill goes down!"

I'll have to contest that. The single phase house meter is a Kwh meter. It will read watts accurately regardless of powerfactor. I think you are confusing Kva with Kw. There are meters that log Kvah and, in that case, you are correct that the Kva could be lowered by powerfactor correction. But not watts.

Quote:
"Around 1998 we still took out in Devonport, Auckland NZ, Ferranti FDb meters and Chamberlain & Hookham 10 Amps LR meters which were last tested in 1926. These had an average error of around 7 % at 10 Amps Inom. "

Curious as to whether they averaged fast or slow.

[This message has been edited by WFO (edited 12-25-2005).]

In our area, the meters are all being converted to the digital read out type. Its no fun anymore, I used to love watching the disc spin in the meter on heavy user apps. I take it these are more accurate or harder to tamper with?

[This message has been edited by Sandro (edited 12-26-2005).]

We are going to smart meters next year i guess we will have to either literally swipe the meter with our debit card or go to the local convince store(7-11) and buy a card like the like the pre pay phones.oh joy...

to WFO

Average time from datalogging experience on houses is that the Ave load is around 2 Amps for 20 hrs / day The other 4 hours it can be anything from 2.1 up to 60 Amps.

In general I would conclude that the Ave error is probably around the 3 to 4 % mark which is not too bad cosidering those meters were 70 + years old. The higher loads > 30 Amps are usually drawn around cooking times when ranges and hotwater demands are higher. Winters in Auckland are not that cold and maybe over a 2 month period some form of electric heating is needed to keep the houses warmer and dryer.

Some shorted turns in the current coil counteracted the increase in speed of the disc too.

Remedie: Probably 99 % of these meter have been replaced by now. There might be the odd one around. Because they had cyclo type dials the meter readers didn't complain too much. Usually these were in the old homestaed houses , sometimes on a marble switchboard high up in the dark corners of the hall.

I gor one in my collection and will post a piccie, and ask one of the moderators to insert it.

2 pictures as promised by RODALCO:







BTW Ray, we've still got a lot of them Ferranti's down here, but they aren't quite that old.
Be a while before we get anything electronic here as far as metering goes, we've only just finished installing all the ABB ripple control relays.

Thanks Trumpy for posting the piccies.

Nothing is more reliable long term than the ferraris disc meter, Accuracy wise also they are the best meter available as far as I'm concerned.

Unless you are brainwashed by sales talk what all these electronic meters can do besides recording power usage.

Man, you sure got your money's worth out of them!

I know what you mean about the electronic meters. They'll probably get better, but I'm a little leary about them still. I had one of the meter manufacturers tell me, "Sure, electronic meters are more accurate and have morre features.....but face it. You'll be lucky to get 15 years out of one."

Considering they already cost 3 to 4 times as much, that's not very comforting.

But here's why you'll see them. Deregulation
(or "Re-regulation" as we call it here in Texas) is raising another part of its ugly head. The U.S. Energy Act of 2005 is trying to force everyone to offer TOU (time of use)metering or some equivalent form to all customers within the next two years.
Unfortunately, you just can't get that kind of data from the older disk meters.

[This message has been edited by WFO (edited 12-27-2005).]

Hey, with all the talk about 'standby' power consumption in electronics and how they collectively suck up precious hydro over the long run, how much consumption does the actual meter use and add to the power users bill?

I just had a case where the homeowner was complaining about excessive billing for the 2 years they were in the house. Utility changed out meter once...no change in bills and they told him removed meter was OK. A smoked HVAC fan motor prompted a call to an electrician who discovered a line-to-neutral imbalance of voltage...like 90-130 or so at the moment. Classic open/bad neutral situation although the homeowner hasn't noticed the other symptoms such as dim/bright lights, etc. Electrician contacts the utility who comes out and does a lot of work. Problem solved...bills down to what the homeowner thinks is reasonable. Now, I am told that the typical Form meter used in single phase 3 wire residential applications is non-Blondel compliant and reads all line-neutral usage at 1/2 the current and twice the voltage. Therefore, an imbalance in line voltages will undermeter some loads and overmeter others...the net effect depends on the load distribution and the imbalance. 240 volt loads will always be metered correctly. Anyone ever heard of this effect?

You are correct.

Each current element of a form 2 meter is designed to produce 1/2 the flux proportionate to the current going through it. The left hand half of the element being wound opposite to the right hand element. And, as you mentioned, the potential coil is connected across each leg (240 volts).
If a 120 v load is pulling "A" amount of current (and for simplicity assuming Watts = Volts x Amps and ignore PF), then 240 x 1/2 A = Watts.

Which of course, is the same as 120 x A = Watts.

For a 240 volt load, the "A" current is returning in the other leg of the meter current coil in the opposite direction. But since the coil is wound in reverse, the flux fields "coming and going" are cumulative.

So 240 volts x (1/2 A + 1/2 A) = Watts.

Which of course, is the same as 240 x A = Watts.

So take an unbalanced load....100 amps on one leg and 10 on the other; and assume a 4 volt drop in the service wire on the heavier loaded leg.

Actual watts,
(116 volts x 100 amps)+(120 volts x 10 amps)=12800 watts or 12.8 Kw.

The meter sees,
236 volts x (1/2 of 100 amps + 1/2 of 10 amps) = 12980 or 12.98 Kw

Or a 1.4% overcharge (if I did my math right). It pays to be balanced for more than voltage drop. Of course, I'm just grabbing arbitrary values at random here.

Hey RODALCO...how about checking my math. Did I blow it?



[This message has been edited by WFO (edited 12-27-2005).]

Your maths look right there WFO.

Under these very unbalanced conditions that meter still does a very good job considering that a class 2 meter is allowed a ± 2.5 % error and is well within its specs.

In general the bit over and under measurements will cancell each other out longer term.

In case of broken neutrals there are usually a lot of problems with blowing lightbulbs if exposed to a high voltage for too long or appliances not working properly.

HAPPY NEW YEAR !! Ray.

Is that also true for electronic meters?

I recently used Hager electronic meters in the tenancies of a shopping centre. One tenant managed to reduce his bill considerably by changing the C/T ratio setting. It didn't occur to me when I selected them that there was nothing stopping anyone from doing so.

Were these direct reading electronic meters or did they have a multiplier attached ?

Direct reading on some tenancies, connected to C/Ts on others. The C/T meters have a button on the front for setting it to the ratio you are using so that the meter shows actual usage instead of having to multiple
the reading.

[This message has been edited by briselec (edited 01-01-2006).]

These tenants must have been able to change the CT ratio via that button or "ZAP" the meter by means of an HV surge nearby.

In my years in CT metering I have found the odd CT meter ( electromechanical ) with the wrong multipler, eg. X 30 ( 150 / 5 Amps )while the CT's were at X 80 ( 400 / 5 Amps ). The meters we used at WEPB were mostly --/5 Amp ( blank 5 )meters and the readings needed a multipler attached to it.
These were on multitap CT's 150/250/400/5 Amps.
Can't prove wheather it was an utility error or changed CT tappings at a later stage by persons unknown.
A lot of CT chambers have seals missing in tenancy buildings.

Links left closed at testblocks or blown potential fuses were more common findings at CT checks in the field, or the transposed phase to current circuit.

JES
I have heard of this happening recently. It cut the Home Owners bill in Half after the utility fixed the problem on the pole. But i don't know what the problem was or what they did to solve it. He didn't notice any dim lights or any other symptoms.

Quote biselec:
"Is that also true (meters not being RMS) for electronic meters?"

No, I believe all (most?) of the electronic meters are true RMS.

Germany has a TV show about meter tampering and power theft discovered by the PoCos... the most funny episode I remember was about a family from Turkey... the guys from the PoCo found a case of electricity theft and the tenant ratted about some other people stealing power too. Getting there the guys were greeted by a woman with several children in the hallway (you know, classic cliché here). They opened the meter closet, only to find a hole drilled into the meter and a needle inserted to keep the disc from spinning... now here comes the funny part. The woman said: "Meter broken! Had fix it!" with a strong accent. To thee PoCo guy's blank faces she added: "Was broken! Always turn!" with a motion of turning her hand to imitate the spinning disc...

Here the way most common way to steal power is simply tapping into the wiring ahead of the meter. In most old multifamily buildings that wiring is easily accessible and can be isolated by means of main fuses that everybody can operate.

The oldest meters I've seen in use date from the mid 1960ies and are swapped for checking every 15 years. If they test ok they're reinstalled for another 15 years.

Digital meters didn't really catch on here. I've seen only one in all my time and that was a huge 60A three-phase meter (that's the largest direct meter available here, everything above 400V 3ph 60A is on a CT).