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Utility meter--always accurate?

Tropical_Helper

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Mar 15, 2021
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I have a curious question... I've been helping a friend research solar and other options for his rural property in Thailand. In the process, I was wondering about a voltage drop that he has on his existing grid feed, so I decided to use a couple of these meters to monitor his power--one connected at his light meter, and the other one at his 100A cutoff switch at his property (more than 1000 yards away). Anyhow, here's the meter I'm using:

1560675742_ScreenShot2021-06-01at12_02_03PM.png.21d17261b4803f6959573d751e084782.png

I put one at both ends of the line because I can see at a glance what the voltage is at either end as well as the load in watts or amps. These meters also have accumulated Kilowatt hours, so naturally I was eager to see how many kilowatt hours we are actually getting at the property versus what we are using straight out of the utility's meter. (Perhaps I should mention, my friend's property is the only one with houses in this 1000-yard distance from the nearby village, and the village is the closest existing place to connect to the utility/grid. Therefore, that's where their light meter is.)

I also noted the utility's meter reading when I began monitoring with my digital meters. After running with these meters for 5 days, I subtracted the difference with all three meters, and here's what I found:

Utility meter: 200 kwh of usage
My digital meter attached to the utility meter: 150 kwh of usage
The meter at my property: 120 kwh of usage

Now 150-120=30kwh, and I was not surprised that we lost 30kwh (20%) on the line from the meter to the property since the wire is too small. What I can't explain is, why is the utility meter reading so much higher than my meter that is hooked up directly to it?

I thought perhaps the induction current detector (the clamp-on device to the right of the meter in the photo above) might be flaky, so I checked the amp reading on that meter against my clamp-on meter, and they basically agreed (within 5% at least).

We actually had someone out here from the utility this morning, and I asked them about the difference. Unfortunately, I don't understand what all they said in Thai, but my translator said it was something about a voltage drop from the light meter to my meter, or something about power being consumed inside the utility meter. Either way, sounds kinda fishy to me since my meter is hooked directly up to the output of theirs. Could my "cheap" meter be that far off?

What do you think?
 
What do you think?

Is your clamp meter also measuring voltage directly? Many clamp meters do not and assume a voltage value. If the voltage assumed by the meter is not the same as actual voltage, the calculated power value will be out.

Does the utility meter also account for variable power factor? Utility meters can often measure both effective and apparent power (which will vary depending on the power factor), and depending on the way energy is billed, either may be used for billing.
 
1. My clamp meter is only reading amps, not watts. So I'm comparing the "amps" on the meter that is wired in (picture shown above) with the amps on my clamp meter.

2. The utility meter (didn't think to show a picture) is the "old style" spinning wheel type, which, I assume, doesn't take into account variable power factors. (We don't have a more modern digital meter, which I assume would be necessary to take the "power factor" into account as well as adjust the billing rates for peak usage, etc.)
 
My clamp meter is only reading amps, not watts. So I'm comparing the "amps" on the meter that is wired in (picture shown above) with the amps on my clamp meter.
If it's not reading watts, how is it generating an energy reading as per the following statement?

My digital meter attached to the utility meter: 150 kwh of usage
If it's providing an energy reading, then it must be measuring, or estimating, power. To measure power requires measurement of current and voltage.

The utility meter (didn't think to show a picture) is the "old style" spinning wheel type, which, I assume, doesn't take into account variable power factors.
That's correct, those older meters will only measure real power. They can lose accuracy but in general are pretty good, within 2%.
 
Sorry for the confusion... I am speaking of three different meters...

1) The utility meter

2) The digital meter with the picture shown above. (This reads volts, amps (using an induction coil), watts, kva, current power factor, and kWh.)

3) My "clamp meter" (didn't know what else to call it), which is a hand-held portable digital clamp-on meter. I used it to try to verify the (amps and volts) readings of meter #2 above. Basically, it seemed to agree with meter #2. I apologize for the confusion.
 
Is your clamp meter also measuring voltage directly? Many clamp meters do not and assume a voltage value. If the voltage assumed by the meter is not the same as actual voltage, the calculated power value will be out.
I think this is exactly what's happening here . . . . and why his Kwh figures are so far off the mark

Don
 
In my experience, I don't know what meter to believe. With respect to DC from my battery to the controller/inverter, I have an analog current meter between the battery and controller. Also the digital meter like yours also between the battery and controller.

When comparing the current between the analog meter, the digital meter, and the Controller LED readout, I get 3 different readings, and also depends if the battery is charging or discharging. I don't know which one is most accurent.

But since most of all my other readings are from the controller LED panel, I use it for all current readings.

Note that in my case, the current readings are as much as 4 amps difference between meters and gain depending if the battery is charging or discharging.

With respect to A/C current, again a get different readings between my controller LED panel and a handheld "True RMS" current meter. The hand gives a study reading while the controller LED readings fluctuate a lot and I just have the guess what I think the average reading is.
 
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