Do electric meter show KW rating that house uses at instantenous.

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Designer101

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California
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Solar and ESS Designer
I always had impression that utility meter always shows aggregated values in Kwhr, that means energy usage data is given,
do California SCE/SDGE meter shows KW rating too??
 
Designer101 said:
I always had impression that utility meter always shows aggregated values in Kwhr, that means energy usage data is given,
do California SCE/SDGE meter shows KW rating too??
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Do you mean a display of the instantaneous kW passing through the meter? Of what use would that be?
 
ggunn said:
Do you mean a display of the instantaneous kW passing through the meter? Of what use would that
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some's solar sales rep are not convinced with breaker derate load calcs , they just want to derate the breaker to 150A from 200A. NEC based load calcs doesn't support that derate, they even challenged me to visit home and run all the laods and read that instatenous Kw from meter, i was not sure we could do that at first place.
 
PG&E digital meters display kW on a cycle with other info. It's not a super accurate method (and not code compliant) but if you're mainly trying to prove it to the homeowner and not the AHJ, then yes you can probably read off the meter.
 
Designer101 said:
some's solar sales rep are not convinced with breaker derate load calcs , they just want to derate the breaker to 150A from 200A. NEC based load calcs doesn't support that derate, they even challenged me to visit home and run all the laods and read that instatenous Kw from meter, i was not sure we could do that at first place.
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Very few (if any) utility meters care about truly instantaneous power. It is possible to measure it of course, but the typical granularity that a utility would care to measure, is demand, which is a 15-minute interval power data. That is, when applicable to the service agreement with the utility. This is the most granularity you need to care about for purposes of justifying reducing a main breaker from 200A to 150A. This would ignore the short spikes when motors start-up and draw their inrush current, but that kind of short term load exceeds its own branch breaker trip rating all the time. Breakers take several minutes to trip under moderate amounts of overload, so the standard 15 minute demand interval is realistic to consider for justifying changing your main breaker rating.

However, it is rare that this data will be available at the scale of a residential application, as most meters for services that small will only measure cumulative kilowatt-hours, rather than demand interval data. High power commercial services might have demand data available already, but for most residential applications, the meter isn't sophisticated enough to keep track of that detail of the data. If necessary, you can put your own customer-owned recording meter on the service and log the interval data. There are meters that can measure this data as granular as 5 minutes.
 
jaggedben said:
PG&E digital meters display kW on a cycle with other info. It's not a super accurate method (and not code compliant) but if you're mainly trying to prove it to the homeowner and not the AHJ, then yes you can probably read off the meter.
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What kW value would it be displaying? The kW value in the present minute? The peak kW value in the past hour? When would it have measured the kW value that it would display?

There could've been twice the kW as the rate of consumption two hours ago, and that would be in your blindspot.
 
Carultch said:
What kW value would it be displaying?
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The smart meter LCD cycles through 3 different displays with an ~15s cycle time. The current power display is up for ~5s. It typically varies each time through. So worst case I infer it is a 15s average power. I think I have seen the power valve change during the 5s display time, in which case is a shorter time average, maybe 1 or 2 seconds, not sure about that.

Cheers, Wayne
 
What Wayne said. It's basically the instantaneous kW, although it probably doesn't update more often than every second at the fastest. I am always comparing my battery system meters to it to make sure I've got them configured correctly.
 
jaggedben said:
What Wayne said. It's basically the instantaneous kW, although it probably doesn't update more often than every second at the fastest. I am always comparing my battery system meters to it to make sure I've got them configured correctly.
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kW is just instantaneous. No updating involved.
 
Our meters (and many others I have looked at) store the max kW until it is reset either from the office or from the field. It’s the demand kW. We generally reset ours twice a year to pick up winter and summer peaks.

Some will display “PD” with the number, which is peak demand.


Some, like the one Jaggedben is talking about (I believe) show on the third window, the voltage and present kW.
So the meter may read
88888 (To show all dials work)
02845 (Example only, kWh)
242v .289kW ((voltage level and instantaneous kw)
There MAY also be a demand screen, depending on how the meters are configured at the shop. Soft keys are programmable.
 
Hv&Lv said:
Our meters (and many others I have looked at) store the max kW until it is reset either from the office or from the field. It’s the demand kW. We generally reset ours twice a year to pick up winter and summer peaks.
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Yes, max kW. I've seen those with a 30-minute maximum. Jaggedb used instantaneous kW.
 
many smart meters quite capable of displaying quite a bit of information, though they likely need peripheral connected components to use gain access to a lot of that information. Some I have seen you can hold a magnet to a particular spot and it will go into a mode that shows some additional information that doesn't appear in normal display mode. In particular you can display instantaneous VA, kW or even display the present power factor with ones I seen around here. Maybe most recent peak demand depending on what time periods are configured for comparing.

I know they also tell you phase angles and volts from a particular reference.
 
kwired said:
many smart meters quite capable of displaying quite a bit of information, though they likely need peripheral connected components to use gain access to a lot of that information. Some I have seen you can hold a magnet to a particular spot and it will go into a mode that shows some additional information that doesn't appear in normal display mode. In particular you can display instantaneous VA, kW or even display the present power factor with ones I seen around here. Maybe most recent peak demand depending on what time periods are configured for comparing.

I know they also tell you phase angles and volts from a particular reference.
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Correct. That particular spot is at the four o’clock position on the side of the meter all the way toward the front.
 
jaggedben said:
My point was simply that what it shows appears to be the instantaneous kW whenever the screen updates. And the value displayed might be from as long as a second or two ago, because the screen doesn't seem to update faster than that.
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I can understand that. For instantaneous you would need something like an analogue Watt Meter.
 
Carultch said:
There's probably some degree of time-averaging, at least over the full period of the waveform cycle, rather than measuring the truly instantaneous product of voltage and current.
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With 1/4 cycle sampling (or more) there is no need for any degree of time averaging. It simply samples, gives that value or instantaneous kW.
most meters aren’t configured that way from the manufacturer unless it’s requested.

For some of the GE meters, I can go in with MeterMate software and configure the LCD screen to show the instantaneous kW when the screen comes up. Is it exact for the time the screen comes up? No. BUT any analog or any other meter can’t do that either because the time it takes our brain to register what we are looking at the instantaneous kW has changed. For an analog meter that shows changing values isn’t exact either, but it’s close enough.

For the GE I-210+c, from the specifications for the meter chip:
“The meter chip has a 22-bit delta-sigma ADC with an effective sampling rate of 2520 samples per second.”
 
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