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Author Topic: How can a disconnected electricity meter still run up a reading?  (Read 965 times)

Offline pmg1410

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Thank you for adding me here.

10 years ago we demolished our property, with the idea that we would eventually rebuild and once the electricity meter was disconnected and the reading was taken, we stored it in our basement.  It was an old type meter, A52 if that means anything to anyone.

My boys are always tinkering, and finding out how things work and unearthed this old box with the meter in it.  I had forgotten it was even there, and the shout immediately went up, "Can we have it" :)

I didn't see any harm, but my husband pulled the plug on their enthusiasm yadda yadda yadda, but when he was repacking it, he noticed that all the little dials, the numbers in the boxes were almost off line, squint, and all of the little boxes had a number.  Weird!!

Being someone who never throws anything away, I fished out the old bills for this meter, (we have a smart now) and realized that indeed the meter seems to have been turning for the last 10 years, while buried in a box.

Before I give the go ahead and let them take it to bits to find out how this is even possible, I thought I would ask here first.

Please phrase all topics as a question, as per site guidelines - moderator.
« Last Edit: 01/12/2015 10:50:04 by evan_au »


 

Offline evan_au

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Please check and correct my numbered assumptions:

(1) I assume that this is a traditional electromechanical electricity meter with a rotating aluminum disk?

From the description of "little dials" or "numbers in the boxes", I can't tell if this is:
- The older type with a series of clock faces side-by-side
- The newer type with an odometer-style display
- You can see examples of both types here: http://en.wikipedia.org/wiki/Electricity_meter

(2) Is it a clock-style meter?

The odometer type always displays a single digit in the window - all except the least-significant digit. These are relatively easy to read.
However, the clock-style display is very easy to misread, because the moving hand is almost always partway between two digits. To make it more complicated, the pointer is driven by gears such that every second clockface goes in the opposite direction(!).
You can get instructions for reading them here: http://www.agl.com.au/residential/help-and-support/how-to-read-your-meter

It is a known problem with electricity meters that if you leave them attached to mains voltage, but with no current flowing through them, the disk will vibrate. If they are not adjusted properly, the disk can actually rotate steadily. (I once had a holiday job repairing and calibrating these electromechanical meters..)

The standards for electricity meters dictate that there is a certain power consumption below which they must not rotate continually. If you have a load which is very reactive (eg a capacitor), you can sometimes get them to rotate despite this requirement.

However, from the description that the house was demolished and the disconnected meter was stored in the basement, (4) I presume that it has had no voltage applied all this time?

Moderately old meters have magnetic bearings, and rotate very freely. However, it would take a very strong external magnetic field to rotate the aluminum disk with no AC voltage applied.

(5) Was it stored up against an electric motor or similar?

Overall, I am guessing that the most likely cause for the difference from your final bill is that you have misread a clock-style meter.
 

Offline pmg1410

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Thank you for your reply.

(1) this is the old type with the rotating disc yes.

(2) Not the clock style, in fact I have a picture of it as my eldest is currently researching online.  Thank you for the links

(4) No power to it since 2004

(5) It was stored at the back of the garage of our now property adjacent to the property that was demolished.  Over the years, the boat was parked in there, and an old car, nothing of a magnetic field that I can think of.

 

Offline evan_au

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Quote from: pmg1410
the numbers in the boxes were almost off line
OK, I see what you mean.
There is a valid occurrence when multiple digits can be out of alignment: When the displayed number wraps around from (say) 9999 to 0000.

However, the image seems to be showing a different transition, with one of the digits between 0 & 1, while the other is between 4 & 5. The two digits to the right seem to be showing "22".

This suggests to me that the meter was subjected to a significant mechanical shock, causing two of the wheels to jump out of alignment, without using the "carry wheels". An explanation of how a mechanical counter works can be seen here:


Where I live, the meter has officially remained the property of the electricity supply company. But if they have gone to electronic meters, I guess they would have little interest in the one in your garage!

These old electromechanical meters allow you to see how things worked, without peering into the microscopic workings of a wristwatch. Modern electronic devices have no moving parts, and the parts that are present are near-microscopic anonymous black prisms.

I think education works better if children occasionally have an opportunity to peer inside the black box.
 
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