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Therefore, the true definition of Horse Power is: 1 hp = 33,000 ft·lbf/min{Reference:http://en.wikipedia.org/wiki/Horsepower|http://en.wikipedia.org/wiki/Horsepower}

So, in essence, the term "horse power" is simply a standardized measurement of how much work a power source can supply.

The power factor is a number which tells to what extent the motor voltage and current are out of phase from one another. Unlike pure resistive circuits like electric heaters and incandescent lights, motors operate with strong magnetic fields present. The magnetic fields add a new element of magnetic resistance to the motor circuit, which throws the voltage and current out of phase from each other. When the voltage and current are not in phase Ohm's law will not work unless the power factor is used to correct for this phase difference. The power factor listed on a motor must be considered when making motor horsepower and current calculations.

The service factor can also be multiplied times the FLA of the motor to give the absolute highest operating amperage the motor should be allowed to operate with under any conditions.{Reference:http://www.bacharach-training.com/norm/electric.htm|http://www.bacharach-training.com/norm/electric.htm}

Where:

- E = Volts
- I = Amperes
- EFF = Efficiency (decimal)
- PF = Power factor (decimal)
- HP = Horsepower

Example: What is the actual horsepower output of the following motor
if its actual measured current draw is 16 amps?

5 HP, 230 Volts, FLA 20.72

Eff(%) 0.86, PF 0.91, SF 1.15

HP = (E x I x EFF x PF) / 746

HP = (230 x 16 x 0.86 x 0.91) / 746

HP = 2880 / 746

HP = 3.86 Hp

5 HP, 230 Volts, FLA 20.72

Eff(%) 0.86, PF 0.91, SF 1.15

HP = (E x I x EFF x PF) / 746

HP = (230 x 16 x 0.86 x 0.91) / 746

HP = 2880 / 746

HP = 3.86 Hp

The three-phase motor is 73% more powerful than an equivalent single phase motor of the same voltage and amperage. The is reflected by the factor 1.732 in the equations below. The factor 1.732 is the square root of the number 3 representing the 3 phases.

Example: Prove that the actual horsepower output of the following motor
is the same as the manufacturers specifications at FLA?

1 HP, 230 Volts, FLA 2.8

Eff(%) 0.84, PF 0.82, SF 1.25

HP = (E x I x EFF x PF x 1.732) / 746

HP = (230 x 2.8 x 0.84 x 0.82 x 1.732) / 746

HP = 768.293 / 746

HP = 1.03 Hp

1 HP, 230 Volts, FLA 2.8

Eff(%) 0.84, PF 0.82, SF 1.25

HP = (E x I x EFF x PF x 1.732) / 746

HP = (230 x 2.8 x 0.84 x 0.82 x 1.732) / 746

HP = 768.293 / 746

HP = 1.03 Hp