Voltage Drop, Three Phase
Also known as three phase VD
Worked example: 50 A, 100 m, 25 mm² copper → 5.96 V drop — press Try an example to run it live, then adjust anything.
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Voltage Drop, Three Phase explained
On a balanced three-phase circuit the three currents sum to zero, so no return conductor carries them home. Each line drops ρLI/A line-to-neutral, and converting that to a line-to-line figure multiplies by √3 — which is why three-phase drop is only 86.6% of the single-phase drop for the same current, length and cable. Running 50 A 100 m on 25 mm² copper gives 1.732 × 1.72e−8 × 100 × 50 / 25e−6 ≈ 5.96 V, about 1.2% on a 480 V system.
This resistive form is what most codes accept for typical building circuits, but it ignores reactance. On large conductors, long runs, or poor power factor, cable inductance adds its own drop and the true answer needs Vd = √3 I (R cos φ + X sin φ). For 4/0 and larger, or anything over a few hundred feet, use the impedance tables — the resistive answer can be optimistic by a third.
Voltage Drop, Three Phase formula
- = Line-to-line voltage drop (V)
- = Conductor resistivity (Ω·m)
- = One-way run length (m)
- = Line current (A)
- = Conductor area (m²)
Missing one of these? Work it out first, then come back
- Line-to-line voltage drop — Three-Phase Real Power, Single-Phase Real Power with Power Factor
- Conductor resistivity — Voltage Drop, Single Phase, Skin Depth
- One-way run length — Voltage Drop, Single Phase, Studs on a Wall at a Given Spacing
- Line current — Three-Phase Real Power, Single-Phase Real Power with Power Factor
- Conductor area — Voltage Drop, Single Phase, Conduit Fill