Power factor is ratio of watts to volts-times-amps. It is possible with AC for amps to be more than watts divided by volts. Amps with AC can be broken down among "real", "reactive" and "harmonic". Ideal resistive loads draw only "real" amps. Watts is volts times "real" amps.

Total amps (square root of sum of squares of real, reactive and harmonic) is what heats up wiring, fuses, breakers, and transformers. But electric meters only bill for watts. Non-"real" amps do not increase your electric bill, except by a minor amount for losses of wires carrying them, and then you only get billed for wiring losses downstream of your electric meter.

If you are concerned about fuel consumption by generators and environmental impact, rest assured that non-"real" amps have only a fraction as much impact there as "real" amps do. Also, a compact fluorescent lamp that is not "high power factor" usually draws less total amps than does an incandescent of same light output.

Now, why are "non-real amps" and power factor a concern? Power companies have a need to get income from their investment in wiring and transformers upstream from your electric meter. Wires and transformers heat as much from non-"real" amps as from "real" amps. Electric companies are known to hit commercial and industrial customers with requirements of billability of the supply capacity, and it is somewhat known that a common requirement is power factor at least .8 (billable watts at least 80% of volts times total amps).

Screw-in compact fluorescent lamps not specially made to have "high power factor" often have a power factor of only around .5, sometimes closer to .4. Some with integral electronic ballasts sometimes have "harmonic amps" so high as to have power factor around .35. Some screw-in compact fluorescent lamps even came with advice as to limitation of number of them to use on a 15 amp circuit, with that number being not much more than is the number of incandescents of equivalent light output that a 15 amp circuit can support.

Meanwhile, high power factor compact fluorescent lamps are only necessary for
commercial and industrial electricity customers using a large number of
compact fluorescent lamps, or using a moderate number and otherwise having
a borderline total power factor. Most lighting in most commercial and most
industrial locations is non-compact fluorescent, with ballasts having high
power factor. But if new construction or a major remodel job involves a
large number of compact fluorescent lamps, then it may be necessary to use
ones with high power factor.

(As a side note - major compact fluorescent installations in commercial,
institutional and industrial locations tend to have ballasts as part of the
fixture and in such a case such fixtures take ballastless non-screw-base bulbs
such as 13 watt twintube/PL and 26 watt doubletwintube/PLC. Where there is
such an installation, it is necessary to determine the need for the ballasts
to have high power factor.)

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Written by and copyright 2007 Don Klipstein.

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