Power Supply FAQs
  • Questions about active power factor correction (PFC):

    • So what if I have a poor power factor?

    • Most consumers are charged per kWh (kilowatt hour) by their utility company. Fortunately, for the customer, poor power factor does not typically affect how much wattage your computer uses. But poor power factor does have an affect on how much power the utility companies can deliver. This means that the utility companies either have to increase their grid's capacity to compensate for the increased power load, charge per kVA instead of per kWh (some commercial/industrial accounts are charged per kVA while residential customers are still charged per kWh), charge a "power factor penalty charge" (which can be applied to customers with power factors even as high as .95!) or make it mandatory for all appliances sold in the country to have a power factor of .96 or better. The EU believed the latter of these to be the best solution, so as of January 1st of 2001 the EN61000-3-2 was put into place imposing limits on the harmonic currents drawn from the mains. In other words, if you're in the EU, you are REQUIRED to have a power supply with power factor correction. Power factor correction is not (yet) a requirement in the U.S. .

      Poor power factor can also limit how much current you can draw from a circuit.  If you’re using a 20A breaker and are drawing a total of 15A in “real power” and the power factor is only .70, then you are drawing an apparent 21.4A, thus overloading the breaker.

      Also, one of the requirements for a computer power supply to be considered "Energy Star" compliant is that it has a power factor of at least .90.

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