Power factor measures the phase angle between the instantaneous voltage and the instantaneous current in a circuit. Voltage (E) leads current (I) by 90° in an inductive (L) circuit and voltage (E) lags current (I) by 90° in a capacitive (C) circuit. A popular mnemonic is ELI the ICE man since E is leading (coming before) I in ELI, and E is lagging (coming after) I in ICE. power factor ( Pf ) = cos ( q ) | 
| Apparent Power ( P ) = I * V | True Power = P | I = Current | q = Phase angle | V = Voltage |
Power Formulas | Apparent Power P = I * V P = I2 * R P = V2 / R
| True Power P = I * V * cos (q) P = I2 * Z * cos (q) P = V2 * cos (q) / Z P = Pa * Pf
| Impedance Z = V2 * cos (q) / P Z = P / [I2 * cos (q)]
| Current I = P / [V * cos (q)] I = sqrt {P / [Z * cos (q)]}
| Voltage V = P / [I * cos (q)] V = sqrt [P * Z / cos (q)]
| | where
| P = power in Watts V = Voltage in Volts I = current in Amps R = resistance in Ohms (Ω) Z = impedance in Ohms (Ω) q = phase angle between I and V in degrees Pa = apparent power in Volt·Amps (VA) Pf = power factor |
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