3 Phase Voltage Drop.

What Is a 3 Phase Voltage Drop Calculator?

A 3 phase voltage drop calculator is used to accurately size industrial and commercial feeders, preventing you from using single-phase formulas that will oversize your wires. In a balanced three-phase system, the current returns through the other two phases rather than a separate neutral wire. The mathematical relationship between the three conductors, which are 120° apart, gives rise to the factor √3 (1.732) instead of the factor of 2 used in single-phase and DC circuits.

Using a standard single-phase calculator for three-phase circuits would significantly overestimate the voltage drop, leading to unnecessarily expensive oversized wire.

3 Phase Voltage Drop Formula

• √3 = 1.732 (the three-phase multiplier)
• R = NEC resistance per 1000 ft for the selected wire gauge
• I = Full Load Amps
• L = One-way wire distance in feet

How to Use This 3 Phase Calculator

1. Enter the line-to-line voltage of the system (commonly 208V, 480V, or 600V from the transformer nameplate).
2. Type the Full Load Amps from the motor nameplate. For multiple motors on one feeder, add up all the individual FLA values.
3. Select wire material. Aluminum is frequently used for long feeder runs in industry to reduce cost and weight.
4. Choose the planned wire gauge. Start with the minimum size required by NEC ampacity tables.
5. Enter the one-way distance from the panel or MCC to the motor.

The NEC strongly recommends keeping 3-phase feeder voltage drop under 3% to prevent motor stalling during startup surges.