Ohm's Law:

Ohms = Volts/Amperes (R = E/I)
Amperes = Volts/Ohms (I = E/R)
Volts = Amperes x Ohms (E = IR)

Power-- A/C Circuits:

Efficiency = 746 x Output Horsepower
                  Input Watts

Three-Phase Kilowatts= Volts x Amperes x Power Factor x 1.732
                                          1000

Three-Phase Volt-Amperes = Volts x Amperes x 1.732

3-Phase Amperes =            746 x Horsepower              
                  1.732 x Volts x Efficiency x Power Factor

3-Phase Efficiency =           746 x Horsepower              
                      Volts x Amperes x Power Factor x 1.732

Three-Phase Power Factor =        Input Watts      
                           Volts x Amperes x 1.732

Single-Phase Kilowatts = Volts x Amperes x Power Factor
                                        1000

Single-Phase Amperes =          746 x Horsepower       
                       Volts x Efficiency x Power Factor

Single-Phase Efficiency =             746 x Horsepower       
                             Volts x Amperes x Power Factor

Single-Phase Power Factor =   Input Watts  
                            Volts x Amperes

Horsepower (3-phase) = Volts x Amperes x 1.732 x Efficiency x Power Factor
                                             746

Horsepower (1-phase) = Volts x Amperes x Efficiency x Power Factor
                                          746

Power - D-C Circuits:

Watts = Volts x Amperes (W = EI)

Amperes = Watts  (I = W/E)
          Volts

Horsepower = Volts x Amperes x Efficiency
                         746

Speed - A-C Machinery:

Synchronous RPM = Hertz x 120
                     Poles

Percent Slip = Synchronous RPM - Full-Load RPM  x 100
                      Synchronous RPM

Motor Application:

Torque (lb.-ft.) = Horsepower x 5250
                          RPM

Horsepower = Torque (lb.-ft.) x RPM
                      5250

Time for Motor to Reach Operating Speed (seconds):

Seconds =       WK2 x Speed Change      
          308 x Avg. Accelerating Torque

WK2 = Inertia of Rotor + Inertia of Load (lb.-ft.2)

Average Accelerating Torque = [(FLT + BDT)/2] + BDT + LRT
                                           3

FLT = Full-Load Torque             BDT = Breakdown Torque

LRT = Locked Rotor Torque

Load WK2 (at motor shaft) = WK2 (Load) x Load RPM2
                                  Motor RPM2

Shaft Stress (P.S.I.) =   HP x 321,000   
                        RPM x Shaft Diam.3

Centrifugal Applications:
Affinity Laws for Centrifugal Applications

Flow1 = RPM1
Flow2   RPM2

Pres1 = (RPM1)2
Pres2   (RPM2)2

BHP1 = (RPM1)3
BHP2   (RPM2)3

For Pumps:

BHP = GPM x FT x Specific Gravity
       3960 x Efficiency of Pump

BHP = GPM x PSI x Specific Gravity
       1713 x Efficiency of Pump

Head in Feet = 2.31 PSIG

For Fans and Blowers:

BHP =          CFM x PSF         
       33000 x Efficiency of Fan

BHP =          CFM x PSW       
       6344 x Efficiency of Fan

BHP =        CFM x PSI       
      229 x Efficiency of Fan

Where:
BHP  = Brake Horsepower
CFM  = Cubic Feet per Minute
FT   = Feet
GPM  = Gallons per minute
PSI  = Pounds per square inch
PSIG = Pounds per square inch gravity
PSF  = Pounds per square foot
PIW  = Inches of water gauge
Specific Gravity of Water = 1.0