ELECTRICAL TOPIC
Three-phase voltage, current and neutral: a practical route
A three-phase answer depends on where voltage and current are measured. This route starts at the conductors and ends with the limits of the balanced model.
A number to keep in view
20,000 W ÷ (√3 × 415 V × 0.80) = 34.78 A
This is line current for a balanced 20 kW electrical-input load at 415 V line-to-line and PF 0.80. It says nothing about motor starting current or an individual winding until the equipment connection is known.
1. Name the voltage before using √3
Line-to-line voltage is measured between two supply lines. Line-to-neutral voltage is measured from one line to neutral. In an ideal balanced star system, 415 V line-to-line corresponds to about 240 V line-to-neutral; in delta, a load branch is across two lines. Write down the measurement points before entering a calculator value.
2. Keep line current separate from winding current
The balanced power formula returns supply line current. In star, that equals current in each load phase. In delta, line current is √3 times each branch current. Neither relationship tells you how to connect a motor; that must come from its actual rating and terminal information.
3. Treat imbalance and harmonics as separate questions
Equal sinusoidal phase currents at 120° cancel in the neutral. Unequal fundamentals leave a vector residual. Nonlinear loads can add harmonic neutral current that the simple three-current formula does not include. Keep the three measured phase readings instead of averaging them into an apparently balanced load.