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Useful Formulas

Formulas for Electrical Motors

To FindDirect
Current
Single PhaseThree Phase
HorsepowerE x I x EFF
746
E x I x EFF x PF
746
1.732 x E x I x EFF x PF
746
Current746 x HP
E x EFF
746 x HP
E x EFF x PF
746 x HP
1.732 x E x EFF x PF
Efficiency746 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 = VoltsI = Amperes
EFF = Efficiency (decimal)PF = Power Factor (decimal)
HP = HorsepowerR = Ohms

 

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Useful Formulas

Formulas for Electrical Circuits

To FindDirect
Current
Single PhaseThree Phase
AmperesWatts
E
Watts
E x PF
Watts
1.732 x E x PF
Volt-Amperes– – – –E x I1.732 x E x I
WattsE x IE x I x PF1.732 x E x I x PF

 

E = VoltsI = Amperes
EFF = Efficiency (decimal)PF = Power Factor (decimal)
HP = HorsepowerR = Ohms

 

Ohms LawCapacitance 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
MaterialK
Aluminum225
Copper234.5
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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