Purpose

Calculate balanced three-phase voltage drop using the three-phase table column and declared power-factor basis.

Learning objectives

• Select three-phase data
• Avoid duplicate root-three factors
• Handle r/x data
• Check line voltage

Three-phase table coefficients normally embody the stated balanced line-to-line relationship. Adding another √3 to a combined mV/A/m coefficient can double-count it.

Core theory

When using a combined three-phase mV/A/m column, follow its formula directly. When using separate r and x components, apply the current Appendix 4 expression with load power factor and phase convention.

Unbalanced loads, neutral drop and triplen harmonics are not proven by a balanced line-voltage calculation. Assess the actual conductor loading and load type.

Motor starting and large step loads may produce a temporary voltage depression far greater than the steady-state result; coordinate with starting method, source impedance and equipment limits.

Assumptions: Coefficient already embodies the table's three-phase relationship; Balanced steady load.

1. Calculate: ΔV = 1.6×80×55/1000 = 7.04 V.
2. Percent: On 400 V, 100×7.04/400 = 1.76%.
3. Do not duplicate: No extra √3 is inserted into this combined-coefficient method.

Illustrative line-voltage drop is 7.04 V or 1.76% of 400 V.

Reasonableness check: The table coefficient is already smaller than comparable single-phase values.

Knowledge check

Answer: When the selected combined three-phase mV/A/m coefficient already includes the relationship. Follow the exact table formula.

Practical exercise

Compare a combined-coefficient result with a supplied r/x and power-factor calculation on the same declared basis.

Summary

• Use the three-phase column
• Do not double-count √3
• Balanced steady drop has limits