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by quickthrowman
1862 days ago
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Lower power factor means more voltage drop over distance as well as more power consumed per unit of work. For a AC 120v 20A single-phase circuit that is 100 feet long with a power factor of 1 (electric heat is pf 1, purely resistive) you can use #12 wire. For the same circuit with a very inefficient inductive load (a crappy motor) that has a power factor of .5, you need to use #8 wire, which is 4x larger (cross section area) than #12. It also requires more power to extract the same amount of work as a more efficient power factor motor. Low power factor equipment wastes electricity and requires more copper. In practice, motors in the US are generally .75 pf (fractional horsepower) or better, .90 pf by 20 HP, and .95 pf as HP approaches 500. These efficiency standards combined with variable-frequency drives means that new electric motors are pretty efficient at using power to do work. https://www.energy.gov/sites/prod/files/2014/04/f15/amo_moto... |
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