Formula for Motor Current

Motor Current Formula:

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

Horsepower (HP):

Voltage (V):

Efficiency (η):

Power Factor (PF):

Motor Current (I):

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1. What is the Motor Current Formula?

Definition: This calculator computes the current drawn by an electric motor based on its horsepower, voltage, efficiency, and power factor.

Purpose: It helps electrical engineers and technicians determine the proper current requirements for motor circuits.

2. How Does the Calculator Work?

The calculator uses the formula:

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

Where:

\( I \) — Current (amps)
\( HP \) — Horsepower
\( V \) — Voltage (volts)
\( \eta \) — Efficiency (decimal, 0-1)
\( PF \) — Power Factor (decimal, 0-1)

Explanation: The formula converts horsepower to watts (746W per HP), then divides by the product of voltage, efficiency, and power factor to get current.

3. Importance of Motor Current Calculation

Details: Proper current estimation ensures correct wire sizing, circuit protection, and prevents equipment damage from overload.

4. Using the Calculator

Tips: Enter HP, voltage, efficiency (default 0.9), and power factor (default 0.85). Efficiency and power factor must be between 0 and 1.

5. Frequently Asked Questions (FAQ)

Q1: Why 746 in the formula?
A: 1 horsepower equals 746 watts, which converts mechanical power to electrical power.

Q2: What's a typical power factor for motors?
A: Induction motors typically have power factors between 0.8-0.9 when fully loaded.

Q3: How do I find motor efficiency?
A: Check motor nameplate or manufacturer specifications. Typical values range 0.8-0.95.

Q4: Does this work for three-phase motors?
A: This formula is for single-phase. Three-phase requires an additional factor of √3 (1.732).

Q5: Why calculate motor current?
A: To properly size conductors, overload protection, and starters for safe operation.