Electric Motor Amp Draw Calculator

Electric Motor Amp Draw Formula:

\[ I = \frac{HP \times 746}{V \times Eff} \]

Estimated Amp Draw (I):

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is Electric Motor Amp Draw?

Electric motor amp draw refers to the amount of electrical current an electric motor consumes during operation. It is a critical parameter for proper circuit sizing, overload protection, and energy efficiency calculations.

2. How Does the Calculator Work?

The calculator uses the amp draw formula:

\[ I = \frac{HP \times 746}{V \times Eff} \]

Where:

\( I \) — Current/amp draw (Amperes)
\( HP \) — Horsepower rating of the motor
\( V \) — Operating voltage (Volts)
\( Eff \) — Motor efficiency (decimal, e.g., 0.85 for 85%)
746 — Conversion factor from horsepower to watts

Explanation: The formula calculates the electrical current required by a motor based on its power rating, operating voltage, and efficiency.

3. Importance of Amp Draw Calculation

Details: Accurate amp draw calculation is essential for proper circuit design, selecting appropriate wire sizes, choosing correct circuit breakers, and ensuring motor protection devices are properly sized.

4. Using the Calculator

Tips: Enter motor horsepower, operating voltage, and efficiency (as a decimal between 0 and 1). All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: Why is 746 used in the formula?
A: 746 watts equals 1 horsepower, so this conversion factor translates mechanical power to electrical power.

Q2: What is typical motor efficiency?
A: Motor efficiency typically ranges from 0.75 to 0.95 (75-95%), with higher efficiency motors being more expensive but consuming less energy.

Q3: How does voltage affect amp draw?
A: Higher voltage results in lower amp draw for the same power output, which is why high-voltage systems use smaller conductors.

Q4: Should I use this for three-phase motors?
A: This formula works for both single-phase and three-phase motors, though three-phase motors typically have additional power factor considerations.

Q5: Why is amp draw important for circuit protection?
A: Circuit breakers and fuses must be sized to handle the motor's starting current (which can be 6-8 times running current) while providing overload protection.