Calculator inputs
Plotly graph
Compare voltage drop percentages and loss values across common standard cable sizes.
Example data table
| System Voltage | Current | Length | Material | Allowed Drop | Suggested Size |
|---|---|---|---|---|---|
| 12 V | 15 A | 5 m | Copper | 3% | 6 mm² |
| 24 V | 20 A | 12 m | Copper | 3% | 10 mm² |
| 48 V | 35 A | 18 m | Aluminum | 2% | 35 mm² |
| 24 V | 8 A | 7 m | Copper | 5% | 2.5 mm² |
Formula used
Voltage drop area: Adrop = (2 × L × ρ × I) ÷ Vdrop
Ampacity area: Aamp = Idesign ÷ (J × Ftemp × Fgroup)
Final required area: Arequired = max(Adrop, Aamp)
Loop resistance: R = (2 × L × ρ) ÷ A
Actual drop: Vactual = I × R
Here, L is one-way length, ρ is conductor resistivity, I is design current, J is current density, and the factors derate capacity for heat and grouping.
How to use this calculator
- Choose whether your load is entered as current or power.
- Enter the DC system voltage and one-way cable length.
- Select copper or aluminum for the conductor material.
- Set the allowable voltage drop percentage for your design goal.
- Adjust parallel runs, ambient temperature, grouped circuits, and safety factor.
- Optionally add a custom current density for your own design standard.
- Press calculate to view the recommended size above the form.
- Use the chart and exports to review or share results.
FAQs
1. Why does the calculator use one-way length?
DC current travels to the load and back, so the formulas internally double the one-way distance. That keeps the input simpler while still accounting for the full loop resistance.
2. Why can voltage drop require a larger cable?
Long runs create more resistance. Even when a cable can safely carry the current, the voltage arriving at the load may fall too much. The calculator checks both limits and keeps the larger size.
3. Should I choose copper or aluminum?
Copper usually allows smaller sizes because it has lower resistance and higher practical current density. Aluminum can reduce cost or weight, but it often needs a larger cross-sectional area for the same job.
4. What safety factor should I use?
A common planning value is 125%, especially when loads may grow or run continuously. Use your project standard, equipment guidance, or applicable code requirement if a specific margin is required.
5. What does grouped circuits mean?
Grouped circuits share heat. When several loaded cables run together, cooling becomes less effective, so allowable current drops. The grouping factor reduces effective ampacity to reflect that condition.
6. Can I use this for solar, battery, or vehicle wiring?
Yes. It works well for general DC applications such as solar arrays, battery banks, RV systems, boats, control panels, and low-voltage equipment, provided you verify final selections against your installation rules.
7. Why offer a custom current density field?
Different organizations use different design rules. The custom field lets you apply your own current density assumption while still using the same voltage drop and derating workflow.
8. Does this replace electrical design review?
No. It is a fast planning and screening tool. Final cable choice should still consider insulation type, terminal ratings, conduit fill, fault levels, code rules, and manufacturer data.