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How much electricity am I using?

J. Brad Grieve

It seems last month's article regarding our electrical bills touched a lot of people here in my reading audience. Thank you for you kind comments and questions. I wanted to expand a little more regarding electricity use in this month’s article.

One of the questions I received several times was how to determine the quantity of electricity each of the apparatuses in a typical house uses. I hope to have some small watt meters soon to help some of my clients. However each house here at Lake Chapala already has a wattmeter pre-installed; it is your CFE electricity meter and the bonus is this method is free.

First look at the front of your electric meter and look for the specification “Kh” which is immediately followed by a number. Many of the new meters will have the specification of “Kh 3 1/33,” which means the Kh factor is equal to 3 1/33 or 3.0303. The next thing you look at is the spinning wheel on the front of the meter. This is the silver disk that is rotating like an old LP record or, for those of you who don’t remember LP records, is spinning like a Compact Disc, only slower.

On the top of the rotating disk are a series of numbers but what we want to do is take note of one point on the disk and count the number of seconds it takes to complete one revolution. If you are using a lot of electricity, the disk will be spinning very fast and if you are using a little electricity, the disk will be rotating slowly. You can count the seconds to complete one revolution of the disk using a stopwatch or other time device (wristwatch) to count the number of seconds.

Now comes the time to pull out the calculator and do some math. The best way to demonstrate this is by using an example. The Kh factor for the meter of my office is 3.0303 (as described above). The number of seconds it took to do one revolution is 72 seconds.

First multiply the Kh factor by 3600. Then divide the result of this multiplication by the number of seconds for one revolution. The final result will produce the number watts consumed. Using the above information for my office, the calculation is as follows:

3600 x 3.0303 / 72 = 152 watts

Sounds like a lot however, this accounts for all the office equipment I have connected to all the various outlets in the walls of my office and all together they are consuming 151 watts. This would mean if I left them on all day and all night for two months (61 days), my electricity bill would be 223 kWh (kilowatt hours) however, the reality is my electricity bill is less than half of that since I turn off my computer, etcetera, at night when I leave the office.

What is interesting about this procedure is now I can turn on the lights in my office and, by counting the seconds for one revolution on the electric meter, determine my new rate of electricity consumption. With the lights on, number of seconds for one revolution was 27 seconds. Therefore the new consumption rate was as follows:

3600 x 3.0303/27 = 404 watts with the lights on

Now, knowing the before and after calculations of my electricity consumption, I know that with the lights on I consume (404-152 =) 252 watts more, which means my lights in the office consume 252 watts when turned on. Considering the slight error in measuring the seconds with a small clock and any loses in the electrical distribution in the walls of my old office, it is very close to the total wattage of the five 50 watt bulbs in the fixture, which add up to 250 watts.

You could repeat this experiment with this in your own home by turning on and off various apparatuses in your own home to determine difference in electricity consumption of every apparatus.

Published or Updated on: February 14, 2008 by J. Brad Grieve © 2008
Contact J. Brad Grieve

J. Brad Grieve is a professional civil engineer who has lived and worked in the Lake Chapala area since 1994. He is the owner of Ajijic Home Inspections and you can be reach him by phone: (376) 766-2836 or e-mail.

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