 Useful Formulas

Formulas for Electrical Motors

 To Find Direct Current Single Phase Three Phase Horsepower E x I x EFF 746 E x I x EFF x PF 746 1.732 x E x I x EFF x PF 746 Current 746 x HP E x EFF 746 x HP E x EFF x PF 746 x HP 1.732 x E x EFF x PF Efficiency 746 x HP E x I 746 x HP E x I x PF 746 x HP 1.732 x E x I x PF Power Factor – – – – – Input Watts E x I Input Watts 1.732 x E x I

 E = Volts I = Amperes EFF = Efficiency (decimal) PF = Power Factor (decimal) HP = Horsepower R = Ohms

Useful Formulas

Formulas for Electrical Circuits

 To Find Direct Current Single Phase Three Phase Amperes Watts E Watts E x PF Watts 1.732 x E x PF Volt-Amperes – – – – E x I 1.732 x E x I Watts E x I E x I x PF 1.732 x E x I x PF

 E = Volts I = Amperes EFF = Efficiency (decimal) PF = Power Factor (decimal) HP = Horsepower R = Ohms

Ohms Law Capacitance in Microfarads at 60 Hz
Ohms = Volts/Amperes (R = E/I)
Amperes = Volts/Ohms (I = E/R)
Volts = Amperes x Ohms (E = IR)
 Capacitance = 26500 x Amperes Volts Capacitance = 2.65 x kVAR (Volts)2

Useful Formulas

Temperature Correction of Winding Resistance

Rc = Rh x

(K + Tc)
(K + Th)

 Value of K Material K Aluminum 225 Copper 234.5
Rc = Resistance at temperature
Tc (Ohms)
Rh = Resistance at temperature
Th (Ohms)
Tc = Temperature of cold winding (°C)
Th = Temperature of hot winding (°C)
Rh = Rc x

(K + Th)
(K + Tc)