📖 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
Vdrop = (√3 × R × I × L) / 1000
- √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
- Enter the line-to-line voltage of the system (commonly 208V, 480V, or 600V from the transformer nameplate).
- Type the Full Load Amps from the motor nameplate. For multiple motors on one feeder, add up all the individual FLA values.
- Select wire material. Aluminum is frequently used for long feeder runs in industry to reduce cost and weight.
- Choose the planned wire gauge. Start with the minimum size required by NEC ampacity tables.
- 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.