3-Phase Motor Full Load Current Calculator

3-Phase Motor Current Formula:

\[ I = \frac{P}{\sqrt{3} \times V \times PF \times \eta} \]

Power (P):

watts

Voltage (V):

volts

Power Factor (PF):

(0-1)

Efficiency (η):

(0-1)

Full Load Current (I):

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is 3-Phase Motor Full Load Current?

The full load current is the current drawn by a 3-phase motor when operating at its rated power, voltage, and frequency. It's a crucial parameter for selecting proper wire size, circuit breakers, and overload protection.

2. How Does the Calculator Work?

The calculator uses the 3-phase power formula:

\[ I = \frac{P}{\sqrt{3} \times V \times PF \times \eta} \]

Where:

\( I \) — Full load current (amps)
\( P \) — Motor power rating (watts)
\( V \) — Line voltage (volts)
\( PF \) — Power factor (0-1)
\( \eta \) — Motor efficiency (0-1)
\( \sqrt{3} \) — Constant for 3-phase systems (≈1.732)

Explanation: The formula accounts for the apparent power (considering power factor) and actual power delivered (considering efficiency) in a balanced 3-phase system.

3. Importance of Current Calculation

Details: Knowing the full load current is essential for proper motor protection, preventing overheating, and ensuring efficient operation. It helps in selecting appropriate starters, contactors, and thermal overload relays.

4. Using the Calculator

Tips: Enter motor power in watts, line voltage in volts, power factor (typically 0.8-0.95 for motors), and efficiency (usually 0.85-0.95 for standard motors). All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between line current and phase current?
A: For delta connections, phase current = line current/√3. For star connections, phase current = line current.

Q2: How does voltage affect the current?
A: Current is inversely proportional to voltage. Higher voltage systems require less current for the same power.

Q3: What are typical power factors for motors?
A: Induction motors typically have 0.8-0.9 PF at full load, lower at partial loads. Synchronous motors can achieve unity (1.0) PF.

Q4: Why include efficiency in the calculation?
A: Efficiency accounts for losses (heat, friction). The actual current drawn will be higher than theoretical due to these losses.

Q5: Can I use this for single-phase motors?
A: No, single-phase motors use a different formula: I = P / (V × PF × η).