COMMON FORMULAS

 

POWER FORMULAS FOR ELECTRIC MOTORS

TO FIND	DIRECT CURRENT	SINGLE PHASE	THREE PHASE
HORSE POWER	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)        HP = Horsepower         PF = Power Factor (decimal)

 

OUTPUT FORMULAS FOR ELECTRIC MOTORS

HORSEPOWER	Torque (lb.ft) x RPM 5250
KILOWATTS	Torque (N.m) x RPM 9550
TORQUE(lb.ft)	Horsepower x 5250 RPM
TORQUE (N.m)	Kilowatts x 9550 RPM

 

SPEED FORMULAS FOR AC MACHINERY

Synchronous RPM	120 x Frequency (Hz) Number of Poles
Percent Slip	Synchronous RPM - Full-Load RPM     x 100                  Synchronous RPM

 

FORMULAS FOR ELECTRIC CIRCUITS

TO FIND	DIRECT CURRENT	SINGLE PHASE	THREE PHASE
AMPERES	Watts Volts	Watts Volts x Power Factor	Watts 1.732 x Volts x Power Factor
VOLT- AMPERES		Volts x Amperes	1.732 x Volts x Amperes
WATTS	Volts x Amperes	Volts x Amperes x Power Factor	1.732 x Volts x Amperes       x Power Factor

 

OHMS LAW

Ohms = Volts/Amperes     (R=E/I)

Amperes = Volts / Ohms   (I=E/R)

Volts = Amperes x Ohms    (E=IR)