Common three-phase formula mistakes
Catch phase-count, voltage-basis, unit, power-factor, efficiency, and load-model mistakes before a three-phase calculator result reaches a design or troubleshooting decision.
- Product
- Three-phase electrical calculations
- Level
- Field triage
- Read time
- 9 min
- Reviewed
- 2026-07-15
- Author
- Toolbox editorial team
- Reviewer
- Technical review
What to establish before troubleshooting
Most three-phase mistakes are not difficult algebra; they are mismatched definitions. Label whether voltage is line-to-line, whether power is kW or kVA, and whether efficiency and power factor apply.
A dimensional and boundary check catches many errors: current should fall as voltage rises for the same power, and adding losses should increase required electrical input.
Abbreviated worked example
See the missing sqrt(3) error
A balanced unity-power-factor load consumes 10 kW at 208 V line-to-line.
- 1Correct: 10,000 / (1.732 x 208) = approximately 27.8 A.
- 2Incorrect single-phase treatment: 10,000 / 208 = approximately 48.1 A.
Result: Omitting sqrt(3) overstates this current by a factor of approximately 1.732.
Caution: If phase voltage and per-phase power are used instead, reformulate the entire calculation consistently rather than adding sqrt(3) by habit.
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