Electrical Motor Horsepower

Overview

Engineering reference data for Electrical Motor Horsepower in electrical engineering.

Key Formulas

Ohm's Law

$V = IR$

Voltage = Current × Resistance.

Power

$P = VI = I^2R = V^2/R$

Electrical power.

Energy

$E = Pt$

Energy = Power × Time.

Variables

Symbol	Description	Unit
$V$	Voltage	V
$I$	Current	A
$R$	Resistance	Ω
$P$	Power	W

Standard Motor Horsepower Ratings

Standard NEMA horsepower ratings for electrical motors from 1 to 4000 hp are shown below. These motors are rated for nominal voltage not exceeding 600 V AC and nominal frequency of 50 or 60 Hz.

Example: DC Motor Shaft Power Calculation

A direct current motor operates at 36 V, draws 5 amps, and has an efficiency of 85%.

Shaft power in kW:

$P_{shaft} = \frac{\eta_m \cdot U \cdot I}{1000} = \frac{0.85 \times 36 \times 5}{1000} = 0.153 \text{ kW} = 153 \text{ W}$

Shaft power in hp:

$P_{shaft} = \frac{0.153}{0.746} = 0.21 \text{ hp}$

References

• Original Source