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I have an Efergy Elite unit that measures the watts used for any circuit its connected to. Right now I'm using it to monitor the circuit with our fluorescent light over the kitchen sink and something puzzling is happening. With just this light on, and the clock on the microwave on, it reads 73 watts. If the light is turned off, it measures 3 watts. So, logically the light is using 70 watts. But here's the thing: the bulb is a 24 inch, 20 watt fluorescent. So how could it be using 70 watts? Could it be the ballast? Or, could it be the bulb. I know this is kind of esoteric, but I'm wondering if anyone has encountered this before, and can explain it. I'm considering opening the wall switch up for the light and putting my ammeter on the hot wire to verify the Efergy reading.

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marked as duplicate by BMitch Oct 10 '13 at 12:50

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While trying to post this question I got directed to a similar question re a Kill-a-watt meter that answers my question too. The bottom line seems to be that these inexpensive meters, like the Kill-a-watt, Reliance Controls THP103, and Efergy Elite will not accurately measure the watts for a CFL because they compute the watts by multiplying amps times volts whereas the power company meter measures watts directly. The former does not take into account the power factor, whereas the latter does.

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