Voltage Drop Calculator
Compute voltage drop in electrical wires. Select system type and enter values.
DC / Single‑phase
Three‑phase
Leave blank for DC (assumed 1)
Voltage Drop
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Enter values above
Percentage
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Resistance (Ω/km)
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Status
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📌 Related Calculators
Voltage Drop Formulas
DC / Single‑phase: VD = 2 × L × I × R / 1000
Three‑phase: VD = √3 × L × I × R / 1000
L – one‑way length (m)
I – current (A)
R – resistance per km (Ω/km) at 75°C
Divide by 1000 to convert km to m
For AC, use R from tables (account for skin effect at larger sizes)
I – current (A)
R – resistance per km (Ω/km) at 75°C
Divide by 1000 to convert km to m
For AC, use R from tables (account for skin effect at larger sizes)
People Also Ask
⚡ What is acceptable voltage drop?
📏 How do I choose the right wire size?
🔌 Why does voltage drop matter?
📊 Copper vs aluminum: which is better?
🌡️ How does temperature affect resistance?
📐 What is the difference between DC and AC voltage drop?
Understanding Voltage Drop
Voltage drop is the reduction in voltage along a cable due to its resistance. Excessive drop can cause equipment malfunction, overheating, and energy loss. National electrical codes often limit drop to 3‑5% for branch circuits.
Factors Affecting Voltage Drop
• Cable length (longer → more drop)
• Current (higher → more drop)
• Conductor size (larger → less drop)
• Material (copper has lower resistance than aluminum)
• Temperature (resistance increases with temperature)
Typical Conductor Resistances (Ω/km at 75°C)
| Size | Copper | Aluminum |
|---|---|---|
| 14 AWG | 8.28 | 13.6 |
| 12 AWG | 5.21 | 8.56 |
| 10 AWG | 3.28 | 5.38 |
| 8 AWG | 2.06 | 3.38 |
| 6 AWG | 1.30 | 2.13 |
| 4 AWG | 0.815 | 1.34 |
| 2 AWG | 0.513 | 0.843 |
| 1/0 AWG | 0.324 | 0.532 |
| 2/0 AWG | 0.257 | 0.422 |
| 3/0 AWG | 0.204 | 0.335 |
| 4/0 AWG | 0.162 | 0.266 |
| 1.5 mm² | 12.1 | — |
| 2.5 mm² | 7.41 | — |
| 4 mm² | 4.61 | 7.41 |
| 6 mm² | 3.08 | 4.91 |
| 10 mm² | 1.83 | 2.94 |
| 16 mm² | 1.15 | 1.84 |
| 25 mm² | 0.727 | 1.17 |
| 35 mm² | 0.524 | 0.841 |
| 50 mm² | 0.387 | 0.622 |
| 70 mm² | 0.268 | 0.433 |
Values are approximate; actual depend on stranding and standards.
Detailed FAQs
How do I use this calculator for AC circuits with power factor?
For AC, the effective current causing heating is I, but the voltage drop depends on the real component of current if using resistance only. In practice, for power factor near 1 (resistive loads), the simple formula works. For motors with low PF, the drop may be slightly higher due to reactive component; this calculator assumes resistive drop using the given current (which is the total current, including reactive). For precise calculations, use impedance instead of resistance.
What is the “one‑way length” and why multiply by 2?
One‑way length is the distance from source to load. In DC and single‑phase, current travels out and back on two conductors, so total resistance is twice the one‑way resistance. For three‑phase, the factor √3 accounts for the phase relationship and the fact that only one conductor per phase is used (assuming balanced load).