Calculator
Enter one-way length, current, system voltage, and cable details. For DC systems, include both positive and negative conductors (round trip) automatically.
Example Data Table
These examples show typical marine and shore-power scenarios. Results are approximate and depend on real cable construction and temperature.
| Type | Voltage | Current | One-way length | Material | Size | Drop (V) | Drop (%) |
|---|---|---|---|---|---|---|---|
| DC two-wire | 12 V | 15 A | 20 ft | Copper | AWG 10 | 0.599 | 5.00% |
| DC two-wire | 24 V | 30 A | 25 m | Copper | AWG 6 | 1.944 | 8.10% |
| AC single-phase | 120 V | 20 A | 50 ft | Copper | AWG 12 | 3.176 | 2.65% |
Formula Used
Voltage drop is modeled using conductor resistance and circuit length. Resistance increases with temperature.
- Temperature correction: R(T) = R(20) × (1 + α × (T − 20))
- DC / single-phase (two-wire): Vdrop = I × RperLength × (2 × L)
- Three-phase: Vdrop ≈ √3 × I × RperLength × L
- Percent drop: %drop = (Vdrop / Vsystem) × 100
- Power loss: Ploss = I² × Rtotal (three-phase uses 3 conductors)
How to Use This Calculator
- Select your circuit type (DC, single-phase, or three-phase).
- Enter the one-way cable length and choose feet or meters.
- Enter the expected load current and your system voltage.
- Select conductor material and wire size (or choose custom resistance).
- Set temperature and parallel conductors if applicable.
- Choose an allowed drop percent, then press Calculate.
- Review volts, percent, pass/fail, max length, and losses.
- Use CSV or PDF export to save your report.
FAQs
1) Why does the calculator use round-trip length for DC?
DC circuits normally use two conductors. Current leaves on the positive and returns on the negative, so resistance includes both paths.
2) What allowed drop percent should I choose?
Many installers target about 3% for critical loads and 10% for general loads. Always follow your vessel, equipment, and local marine guidance.
3) Does temperature really change voltage drop?
Yes. Conductor resistance rises with temperature, increasing drop and losses. Hot engine rooms and bundled cables may run warmer than ambient.
4) Can I use custom resistance instead of AWG?
Yes. If you know the cable’s resistance from a datasheet, enter it as Ω/1000 ft or Ω/km. The calculator will convert units for you.
5) Why is three-phase handled differently?
Three-phase line-to-line voltage drop is often approximated with √3 × I × R × L. This simplified model ignores reactance and power factor details.
6) What do parallel conductors mean here?
Parallel conductors are multiple identical cables sharing current. Effective resistance drops roughly in proportion to the number of parallel runs.
7) Are the example results exact?
They are illustrative. Real voltage drop depends on cable construction, strand count, termination quality, corrosion, and actual operating temperature.
8) What should I do if my drop fails the limit?
Try a larger wire size, shorten the run, reduce current, increase voltage if possible, or use parallel conductors. Recheck after changes before installation.