# Utility meter nameplates, decoded.



## MDShunk (Jan 7, 2007)

Ever wondered what all those numbers, letters, and codes mean on standard utility kilowatt-hour meters? I have. 









Photo courtesy of GE

Here's a little better view of a typical nameplate, with some explanation:









Illustration courtesy of GE

1. The meter serieal number, by the meter manufacturer.
2. Utility information and bar code area. This can be anything the utility company wants.
3. AMR identification number (for automated meter reading)
4. Month and two-digit year of manufacture
5. Assembly location

A little more:









Illustration courtesy of GE

Now, it gets a little more complicated.
1. "Multiply by" constant. With digital meters, the value that you need to multiply the kilowatt reading shown in the digital readout by to get the amount of kilowatt hours. 
2. Current class (continuous rated current)
3. Voltage transformer ratio. Value of the voltage transformer used in digital meters.
4. Current transformer ratio. Value of the current transformer used in digital meters.
5. Nominal voltage.
6. Number of wires for the metered service
7. ANSI C12.10 Form number. Normal plug on meters are called "S" form meters for short, and the old style are call "A" form meters for short. There are many subtle variances within each form class.
8. Watthour test constant. In digital meters, this is the number of watthours metered per digital pulse of the optical pickup.
9. Primary watthour constant. In analog meters, this is the number of watthours metered per revolution of the disk. 
10. Test amp rating. This is the current value, when used at the rated voltage of the meter, to conduct the "full load" and "lag" calibrations.

50 amps for class 320
30 amps for class 200
15 amps for class 100
2.5 amps for class 20
11. Nominal frequency.
12. Catalog number.


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## Paul_NJ (Mar 28, 2007)

The older, analog meters (spinning disc) have a meter factor (typically 7.2 around here in Northern NJ) that could be used to calculate electrical useage in conjunction with a stopwatch. Which I found as a handy way to avoid jamming an Amprobe into a crowded box to track load per circuit when a customer claims their electric bill is way too much. Is there any way to do the same with these newer digital meters?


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## MDShunk (Jan 7, 2007)

Paul_NJ said:


> Is there any way to do the same with these newer digital meters?


Yes, but it requires a special tool. There is an infrared LED on the digital meters that sends information to a small, handheld device for that purpose. It does some other stuff too.


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## MDShunk (Jan 7, 2007)

I might have spoken too soon. Some of the digital meters aparently have an LED that will 'flash' every "disk revolution". There's no disk, obviously, but the flash happens once per revolution as if you did have an analog meter. Every time the LED flashes in a timed minute (for instance), multiply that by the "kh" number on the face of the meter to find the number of kilowatt hours of electricity consumed in that timed minute. Then do the math for amps or watt-minutes whatever else you're solving for.


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## Paul_NJ (Mar 28, 2007)

Wow, I didn't know that. Most meters around here are still the old style, but it's good to know you can do a quick usage "audit" on the digitals as well simply flipping breakers, and using a stopwatch. Thanks!


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