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3-Phase Voltage Drop

Calculate voltage drop for three-phase electrical circuits using copper conductors per NEC standards.
Volts
Amps
feet

The Square Root of 3 ⚡

In 3-phase power calculations, the multiplier 1.732 (which is $\sqrt3$) accounts for the phase shift between the three alternating current vectors. For a single-phase circuit, the multiplier would be 2 (loop length). For 3-phase, the phase relationship makes it slightly less than double.

Voltage Drop

13.86 Volts
2.89% drop

Volts at Load

466.1 Volts
Estimated delivered voltage
SOURCELOADLOSS OVER DISTANCE
For estimation purposes only. Always consult a licensed professional before beginning work. Full Trade Safety Notice →
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What is 3-Phase Voltage Drop Engineering?

Excessive voltage drop in 3-phase systems can cause motors to run hot, equipment to trip, and overall power inefficiency. Sizing conductors for distance is as critical as sizing them for load.

Mathematical Foundation

3-Phase Drop Formula
Vd=1.732×L×R×I1000V_d = \frac{1.732 \times L \times R \times I}{1000}
VdV_d= Voltage Drop (Volts)
LL= One-Way Length (feet)
RR= Resistance in Ohms per 1000ft
II= Current (Amps)

Laws & Principles

  • NEC 210.19(A) Information Note: A voltage drop exceeding 3% at the farthest outlet leads to inefficient operation.
  • The 1.732 multiplier accounts for the 120-degree phase shift in 3-phase power (sqrt(3)).
  • Resistance (R) should be based on uncoated copper at 75°C for standard calculations.
  • Voltage at Load = System Voltage - Calculated Drop.
  • UPSIZE conductors if the percentage drop exceeds the equipment's tolerance (typically 3-5%).

Step-by-Step Example Walkthrough

" 480V, 100A load at 500ft using 2 AWG Copper. "

  1. 1. Find Resistance: 2 AWG = 0.16 Ohms per 1000ft.
  2. 2. Apply 3-Phase Formula: (1.732 * 500 * 0.16 * 100) / 1000.
  3. 3. Calculation: 13,856 / 1000 = 13.86 Volts Drop.
  4. 4. Percentage: (13.86 / 480) * 100 = 2.89%.
Final Result: 2.89% drop. Within NEC 3% recommendation.

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