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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

 

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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

 

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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)

 

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