Advanced Cable Size Calculator
Formula Used
Single phase current: I = P ÷ (V × PF × η)
Three phase current: I = P ÷ (√3 × V × PF × η)
DC current: I = P ÷ (V × η)
Design current: Id = I × safety factor
Area by ampacity: A = Id ÷ effective current density
Single phase or DC voltage drop area: A = 2 × ρ × L × I ÷ Vd
Three phase voltage drop area: A = √3 × ρ × L × I ÷ Vd
ρ is conductor resistivity. L is one way length. Vd is allowed voltage drop.
How to Use This Calculator
- Enter the load value and select watts, kilowatts, or horsepower.
- Choose the system type, voltage, power factor, and efficiency.
- Enter the one way cable route length.
- Select copper or aluminium conductor material.
- Choose the installation condition and correction factors.
- Set the allowed voltage drop percentage and safety factor.
- Press the calculate button to view the suggested cable size.
- Use the CSV or PDF button to save the result.
Example Data Table
| Load |
System |
Voltage |
Length |
Material |
Drop Limit |
Common Result |
| 5 kW |
Single phase |
230 V |
30 m |
Copper |
3% |
6 mm² or higher |
| 15 kW |
Three phase |
400 V |
60 m |
Copper |
3% |
10 mm² or higher |
| 25 kW |
Three phase |
400 V |
90 m |
Aluminium |
5% |
35 mm² or higher |
Why Correct Cable Size Matters
Cable size affects safety, cost, and performance. A cable that is too small can heat during normal use. Heat damages insulation and raises fire risk. A cable that is too large may work well, yet it can waste money and space. Good design balances load current, voltage drop, material, route length, and installation conditions.
What This Tool Checks
This calculator estimates the load current first. It then increases that current by the selected safety factor. The tool compares that design current with a simple ampacity method based on current density. It also checks voltage drop over the cable run. The final suggested size is the first standard area that meets both checks.
Copper and Aluminium Choices
Copper has lower resistance than aluminium. So copper often needs a smaller area for the same load and distance. Aluminium is lighter and can cost less. It usually needs a larger area to carry the same current. The calculator lets you compare both choices before selecting a final cable.
Voltage Drop in Long Runs
Long cable runs create more resistance. More resistance creates a higher voltage drop. High voltage drop can make motors start poorly. It can also reduce lighting output and waste power. That is why the voltage drop limit is important. Many general designs use a limit near three percent or five percent. Always follow the project rule or local code.
Using Results Wisely
The result is an engineering estimate, not a final certification. Real installations also depend on insulation rating, ambient temperature, soil condition, conduit fill, cable tray spacing, harmonics, protective devices, and local regulations. Use the answer as a planning guide. Then verify the chosen size with the applicable wiring standard and a qualified professional.
Better Planning Tips
Enter the real route length, not only the straight distance. Use the correct system type. Select three phase only when the load is balanced across phases. Use realistic power factor and efficiency values. Motors and compressors often need extra starting consideration. Keep records by exporting the result. Compare examples before buying cable. Small checks at the design stage can prevent costly changes later. Label circuits clearly, and keep spare capacity for future maintenance or minor load growth.
FAQs
What is cable size calculation?
It is the process of selecting a conductor area that can carry current safely while keeping voltage drop within the required limit.
Why is voltage drop important?
Voltage drop reduces the voltage reaching the load. Too much drop can cause poor motor starting, dim lights, wasted power, and unstable equipment operation.
Is copper better than aluminium?
Copper has lower resistance and usually needs a smaller size. Aluminium is lighter and may cost less, but it often needs a larger area.
What does safety factor mean?
The safety factor increases the calculated current. It gives extra allowance for normal variation, future load growth, and practical installation uncertainty.
Can this replace electrical code tables?
No. This tool gives an estimate. Final cable selection should follow local wiring rules, protection requirements, insulation ratings, and professional review.
What length should I enter?
Enter the one way route length from supply to load. Include real routing bends, rises, drops, and cable tray distance.
Why do correction factors matter?
Heat and cable grouping reduce safe current capacity. Correction factors lower the effective ampacity so the selected cable is more realistic.
Why is three phase formula different?
Three phase systems share power across phases. The formula uses √3 because line voltage and phase relationships affect current and voltage drop.