I have been trying to check the accuracy of my electricity meter, and
have discovered that the last two red numbers following the main meter
reading appears to record tenths, not hundredths. If this is normal,
why not just have one red number? At he moment, every time it goes up
by ten, the main meter reading increases by one.
Is everyone's meter like that, or do I have a dodgy meter?
I have never had a meter that ha any red numbers,
but I can't imagine a kiloWatt-hour meter that
measured closer than 0.1 kiloWatt-hour.
How are you checking the accuracy of the meter
reading? If you are checking it against stated
watt usage of an appliance, you will likely have a
problem, e.g., a 100 watt light bulb. I've never
tested one that used exactly 100 watts. You
probably need an expensive VOM to read actual amps
and voltage to get accuracy.
You can check the watt usage for very short
periods of time if you want to count revolutions
of the meter disk. On the meter face you will see
a K(subH) = (some number) somewhere. This is a
constant for that particular meter.
Watts (not kilowatts) equals ((number of disk
revolutions) x 3600 x K(subh))/ seconds.
By the way this is a Brit meter so that explain it somehow. I'm
encouraged by your remark that you can't imaging a kWh meter measuring
closer than 0.1. I thought about testing it by turning on my 750 watt
microwave for say, 10 minutes and calculating the desired usage. But
there are other appilances in use, fridge, freezer etc that it wouldn't
I couldn't find a K(subH) that you mentioned. Below the meter reading
there is 240v - S 200.31 - 166 2/3 revs/kWh - 1PH 2W - Class 2 0 -
Floton. Beneath 240v, there is 20 80A and 50Hz. It is a Sangamo Western
meter and is the property of South Eastern Electricity Board. Most of
this is double dutch to me George, but it may mean something to you?
Well, that it explains it, British! :) the 50Hz
is a clue it isn't U.S. since all of our stuff is
60 cycles/second. I haven't looked at British
meters so don't know how to interpret the 166 2/3
revs/kWh, but I would bet it means that the disk
turns 166 2/3 revolutions for each kWh. Solving
the equation that I have you for K(Subh) using 166
2/3 revolutions results in a K(Subh) of 6.00
which is well within the range of the meters I
If you do test something, don't use anything that
has a motor, and certainly not a microwave. (btw
was the microwave 750 watts output or input? If
input that is really a weak microwave since output
could be as low as 600 watts. Straight resistance
is best, for example, turn everything else off and
turn on lights with a total wattage of 1000 watts.
You won't be accurate but you should be within a
If I were you, I would call up the electric
company, ask for a technician, and ask him/her
what everything meant and how to check the
accuracy of the meter (they'll probably do it if
you have had excessively high bills). You might
get nowhere, but you also might get all the info
It is a simple Kwh meter. The numbers you provide indicate which meter it
The best thing you can do is call your supplier and ask for some one to come
out and explain it to you. The 80a means that the meter will handle 80 amps.
Hz is self explanatory.
I have not a clue what the 20 is.
Here in the US meters read left to right. That gives you a number. Some
meters are direct read, they actually read correctly. On large users I have
seen multipliers of 1000. I have seen multipliers on homes of 5-10. Each
meter can and may be set by the utility for a specific purpose.
The odds that you will be able to "check" your meter are astrominical. I
have been working on meters for 20 years. You need specific calibrated
equipment. Utilities where I live are allowed by Arizona law to be within
3%. I know a lot of the meter guys and they established plus or minus 0.5%.
I have seen 3 residential meters out of calibration in 30 years. One was low
and the customer was bitching. He really bitched when they fixed the
problem. Commercial demand meters in the old days were subject to some
whims and could wander out of calibration. I know of one that has been
wrong for 10 years and the customer knows it the utility knows it and they
leave it alone. It took me 6 months and well over 100K of equipment to
prove the meter was wrong. The utility just made an adjustment for that
month and lowered the kwh charge for future bills. End result was the same.
If you think your bill is to high look carefully on your side. Something
running more than it should or a new load. Chances are it is on your side of
the meter not their side.
It might be possible for something in the meter to be awry, odds are against
Everything above is referenced from the USA. Should be close enough for
where you are.
Thanks for taking the time to reply in such detailed manner. All makes
very interesting reading, particularly the complications involved in
checking a meter's accuracy. My reason for originally doubting my
meter's accuracy was that quite a few units get clocked up during the
night. I've turned off all appliances that were previously on standby
or on a clock (microwave, video etc), but I have a fridge/freezer AND a
freezer. The freezer frequently freezes up quickly so I now think that
it is inefficient and is probably the reason. Both are half empty so I
plan to move all contents to the fridge/freezer, turn the freezer
permanently off and see if electric usage drops.
Thanks again for such an interesting insight.
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