DC Cable Voltage Drop Calculator
Calculate cable voltage drop from material, conductor size, length and current. Formula, worked example and a table of typical values.
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Estimate only. Not engineering or safety advice. Check the result against the applicable standard and the equipment data, and have a competent engineer review it before it is relied on. Terms of use.
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Formula
Worked example
| Input | Value |
|---|---|
| Load current | 50 A |
| One-way length | 50 m |
| Conductor material | Copper |
| Conductor size given as | Cross-section (area) |
| Conductor cross-section | 10 mm² |
| Conductor temperature (°C) | 20 |
| System voltage | 230 V |
| Circuit | Two-wire (DC or single-phase AC) |
- A = 10 mm² (given)
- ρ(20 °C) = 1.724e-8 × (1 + 0.00393 × 0) = 1.724e-8 Ω·m
- R = ρ L / A = 0.08621 Ω (one way)
- Vd = 2 × 50 × 0.08621 = 8.6205 V
- Vd % = 3.748 %
Typical values
| One-way length (m) | Voltage drop (V) | Drop as % of system voltage |
|---|---|---|
| 10 | 1.724 | 0.75 |
| 25 | 4.31 | 1.87 |
| 50 | 8.62 | 3.75 |
| 100 | 17.241 | 7.5 |
| 200 | 34.482 | 14.99 |
Other inputs are the same as in the worked example above.
Assumptions
- Resistive load, reactance ignored
- ρ20 (Ω·m): copper 1.7241e-8, aluminium 2.8264e-8, silver 1.59e-8, gold 2.44e-8, nickel 6.99e-8, nichrome 1.10e-6
- α (per °C): copper 0.00393, aluminium 0.00403, silver 0.0038, gold 0.0034, nickel 0.006, nichrome 0.0004
- Round solid conductor when size is given as AWG or diameter
- A custom resistivity is taken as the value at 20 °C
Copper and aluminium use the annealed-copper (IACS) and commercial-aluminium values, which are slightly higher than pure-metal handbook values (copper 1.68e-8 and aluminium 2.65e-8 Ω·m would give a drop about 2.6% and 6.2% lower). The resistivity used is shown beside the result. Stranded conductors have more resistance than a solid wire of the same diameter. For AC circuits with significant reactance or low power factor use the Voltage Drop calculator with R and X from a data sheet.
Frequently asked questions
How is DC Cable Voltage Drop calculated?
Vd = k × I × L × ρT / A; ρT = ρ20 × (1 + α(T − 20)); k = 2 (two-wire) or √3 (three-phase); AWG: d = 0.127 mm × 92^((36 − n) / 39), A = π d² / 4. Worked example: Load current 50 A, one-way length 50 m, conductor material Copper, conductor cross-section 10 mm² gives Voltage drop: 8.62 V · Drop as % of system voltage: 3.75%.
What do I need to enter?
Enter load current, one-way length, conductor material, conductor cross-section, conductor temperature (°C), system voltage and circuit. Change the unit of a value with its selector and the result stays the same.
Why does the formula use a factor of 2?
On a two-wire circuit the current flows out and back, so the current travels twice the one-way length and k = 2. Three-phase uses √3 instead.
What voltage drop is acceptable?
The limit comes from the wiring rules you work to and varies by circuit type and country. The calculator flags a drop above 3% as a common limit for final circuits; confirm against your standard.
Is this suitable for AC cables with large conductors?
It treats the load as resistive and ignores reactance. For AC circuits with significant reactance or a low power factor, use the AC Voltage Drop calculator in Elecmetric.
How accurate are the results?
Every figure comes from the same tested engine as the Elecmetric calculators and is meant for estimating. Check design values against the standard and the equipment data you work to.
Related
Next steps in a design: Cable Power LossVoltage DropWire Gauge (AWG)
Formula guides: Voltage Drop Formulas for CablesDC Lighting Voltage Drop FormulasConductor Resistance Formulas and Temperature
All 78 conversionsVoltage Drop from Conductor Size in Elecmetric