Calculator Inputs
This page uses a single-column content flow. The calculator fields below switch to three columns on large screens, two on medium screens, and one on mobile.
Voltage Drop by Standard Cable Size
The Plotly graph compares expected drop percentages across common conductor sizes using your submitted assumptions.
Example Data Table
| Scenario | System | Voltage | Load Current | Length | Area | Material | Typical Result Trend |
|---|---|---|---|---|---|---|---|
| Lighting Circuit | Single Phase | 230 V | 12 A | 25 m | 2.5 mm² | Copper | Usually modest drop over short runs. |
| Workshop Feeder | Three Phase | 400 V | 48 A | 60 m | 16 mm² | Copper | Often acceptable with balanced loading. |
| Battery Circuit | DC Two-Wire | 48 V | 80 A | 18 m | 35 mm² | Aluminum | Low voltage systems need larger conductors. |
| Pump Motor | Three Phase | 415 V | 72 A | 95 m | 25 mm² | Copper | Long runs sharply increase drop and losses. |
Formula Used
Temperature-adjusted resistance: RT = R20 × [1 + α × (T − 20)]
Resistance at 20°C per meter: R20 = ρ / A
Single phase AC: Vdrop = I × [(2RL × cosφ) + (2XL × sinφ)]
Three phase AC: Vdrop = √3 × I × [(RL × cosφ) + (XL × sinφ)]
DC two-wire: Vdrop = I × (2RL)
Drop percentage: Drop % = (Vdrop / Vsupply) × 100
Power loss: Ploss is estimated from I²R using the loop or phase resistance applicable to the selected system.
In these formulas, ρ is resistivity, A is conductor area, α is temperature coefficient, T is conductor temperature, R is resistance per meter, X is reactance per meter, L is one-way length, and φ is the phase angle.
How to Use This Calculator
- Select current based or power based mode.
- Choose single phase, three phase, or DC two-wire operation.
- Enter the supply voltage and either load current or load power.
- Fill in power factor, efficiency, route length, conductor area, and material.
- Add conductor temperature, cable reactance, parallel runs, allowable drop, and future load margin.
- Press the calculate button to display the results above the form.
- Review voltage drop, percentage drop, load voltage, power loss, and recommended cable size.
- Use the chart and export buttons to document your design review.
Frequently Asked Questions
1. Why is voltage drop important in low voltage systems?
Excessive drop can reduce equipment performance, increase heating, and cause startup or control issues. Low voltage installations are more sensitive because even small absolute losses become large percentages.
2. Why does the calculator ask for conductor temperature?
Resistance rises with conductor temperature. Warmer cables produce more voltage drop and more losses, so the temperature adjustment improves design realism.
3. What is the difference between operating current and design current?
Operating current is the present calculated or entered load current. Design current includes the future load margin, giving a more conservative basis for cable sizing.
4. When should I use power based mode?
Use power based mode when you know the load power but not the current. The page estimates current from voltage, efficiency, and power factor before calculating the drop.
5. Why does three phase usually show lower drop than single phase?
Three phase circuits distribute power more efficiently for the same conductor size. The formula uses a different geometric factor, so drop is often lower than comparable single phase runs.
6. Does reactance matter for short low voltage cables?
For many short runs, resistance dominates. However, reactance still matters in longer runs, larger conductors, and lower power factor loads, especially in AC feeders.
7. How is the recommended cable size chosen?
The calculator checks common standard sizes and returns the smallest one whose predicted percentage drop stays within your allowable limit under the entered conditions.
8. Can I use this result as a final code compliance decision?
Use it as a design aid, not the only decision basis. Final cable selection should also consider ampacity, installation method, insulation rating, grouping, and local electrical rules.