Like a bad penny, this "urban legend" just keeps coming back. Since a kWh meter, whether mechanical or electronic, measures only "real" power, the addition of a capacitor- which adds capacitive reactance- cannot affect real power. A residential customer will never see a reduction in the amount of real power measured by the meter after adding a capacitor. That said, some electronic meters can display and record reactive power and energy- but that is not real power.
The same is not true for an industrial customer that has a large number of motors. A lightly-loaded induction motor will impose a low power factor on the electrical supply system, which then must supply the reactive currents when needed- even though those reactive currents are returned to the source later in the cycle. As a result, the utility must have larger substations and heavier conductors to handle such loads. To force industrial customers to raise their power factors, utilities impose a penalty for low power factors. Most power utilities want their industrial customers to have PF above 95%. So, in this unique case, adding capacitance downstream of the electric meter WILL reduce the power bill, but only because it reduces or eliminates the low PF penalty and not because it affects the kWh consumed. One of the reasons why this so-called "energy saver" sounds attractive is because the average Joe Citizen may think that he can measure power in an AC circuit by multiplying the voltage across the line by the current flowing through the line. That product is volt-amperes, not watts, and it will go down when a capacitor is added- if the power factor is not unity. The only way to correctly measure real power in watts is to use an instrument that incorporates a four-quadrant multiplier, which determines the instantaneous product of volts and amperes throughout each sine wave cycle. Although commercial wattmeters can cost hundreds of dollars, there is at least one device on the market, called the "Kill-A-Watt" which is marketed by several vendors for less than $25. I bought one of these devices, and was surprised to discover that its power readings were within 5% of those displayed on my digital wattmeter. 73, Eric Lemmon WB6FLY -----Original Message----- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Chuck Kelsey Sent: Friday, August 20, 2010 6:00 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Adding capacitors to lower electric bill A while back, maybe a year or two ago, there was a discussion on here where a list member had success adding a capacitor to his electric service which reduced his bill. It was debated for a while. Anyway, I am wondering if the utility company ever came and replaced the spinning disk meters with electronic versions, and if so, what the outcome was. Could the original poster respond either here or privately? I just today had a similar discussion with another ham who tried essentially the same thing with no success - only his was a commercial model, so it cost him considerably more. Chuck WB2EDV
