Fine tuning GEM's voltage to match the Electric companies

[Mustang65]

OK, have been noticing that the monthly kW's that the GEM was reporting were not matching the monthly Electric Companies numbers. GEM's numbers were on the low side. So, I purchased (2) 100 watt incandescent light bulbs. I installed them on different legs of the 120VAC supply. No other electrical things were plugged in at the time of the test. GEM was displaying "0" watts for both legs. Installed the light bulbs, and turned them on. Here are the results:

GEM Voltage = 122.2VAC
Kill a Watt = 119.8VAC
Multi-meter = 120.1VAC

With nothing on the circuits, GEM displayed "0" Watts

Leg-1
Gem Watts Bedroom = 91Watts *
Kill a Watt Bedroom = 99.3Watts

Leg-2
Gem Watts Bathroom = 92Watts *
Kill a Watt Bedroom = 100Watts

* I switched bulbs and got the same readings.

Based on the above numbers, I would say that I have to make some adjustments to GEM. I just a have to figure out what they are.

[ben]

Plug the GEM PT into the Kill-a-watt and calibrate the voltage, adjust the PT Type +-1 until it matches. (Use the GEM Live Data page in the Setup Webpage).

Once those match, try the light bulb again.

[Teken]

It should be noted just because an incandescent bulbs indicates X watts it doesn't mean that is what it will consume.

Using a combination of Ohms Law, Accurate DMM, you can identify the true value. Keep in mind each CT has a tolerance / variability.

[Mustang65]

It should be noted just because an incandescent bulbs indicates X watts it doesn't mean that is what it will consume.

Using a combination of Ohms Law, Accurate DMM, you can identify the true value. Keep in mind each CT has a tolerance / variability.

The Kill a Watt is displaying 99.3 watts on Leg 1
The Kill a Watt is displaying 100 watts on Leg 2.

The watts stayed the same even if I switched bulbs.

You can not get much closer to 100 watts that that. I would say that it is close enough for government work.

[GaryFunk]

The watts stayed the same even if I switched bulbs.

You can not get much closer to 100 watts that that. I would say that it is close enough for government work.

And Never assume the meter is accurate. Every meter operates within a tolerance. Balance each circuit then adjust as needed to match the meter. OR prove the meter is over charging and demand a refund.

[Mustang65]

Plug the GEM PT into the Kill-a-watt and calibrate the voltage, adjust the PT Type +-1 until it matches. (Use the GEM Live Data page in the Setup Webpage).

Once those match, try the light bulb again.

Finally, got around to adjusting the PT voltage. Will check numbers next month
Thank you