Cable Sizing Calculator

Calculator Inputs

Phase

Load Input Mode

System Voltage (V)

Load Power (kW)

Load Current (A)

Power Factor

Efficiency

Cable Length (m)

Allowed Voltage Drop (%)

Conductor Material

Insulation Type

Installation Method

Ambient Temperature (°C)

Grouping Factor

Demand Factor

Safety Margin (%)

Starting Current Multiplier

Example Data Table

Load	Phase	Voltage	Length	Material	Insulation	Suggested Size
15 kW pump	Three	415 V	35 m	Copper	XLPE	10 mm²
25 kW motor	Three	415 V	45 m	Copper	XLPE	16 mm²
8 kW heater	Single	230 V	28 m	Copper	PVC	16 mm²
60 A feeder	Three	415 V	70 m	Aluminum	XLPE	50 mm²

These rows are illustrative examples. Final selections should follow site standards, local regulations, and manufacturer data.

Formula Used

Three-phase current from power
I = P / (√3 × V × pf × η)

Single-phase current from power
I = P / (V × pf × η)

Design current with margin
I_design = I_base × demand factor × (1 + safety margin)

Required tabulated ampacity
I_tab = I_design / (ambient factor × grouping factor × installation factor)

Three-phase voltage drop
Vd = √3 × I × L × (R cosφ + X sinφ) / 1000

Single-phase voltage drop
Vd = 2 × I × L × R / 1000

The calculator first determines the operating current, adds design margin, applies derating, then selects the smallest standard cable size meeting ampacity and voltage drop targets.

How to Use This Calculator

Choose single-phase or three-phase supply.
Select whether you know load power or load current.
Enter voltage, power factor, efficiency, and circuit length.
Choose conductor material, insulation, and installation method.
Set ambient temperature, grouping factor, demand factor, and safety margin.
Click the calculate button to see the recommended cable size above the form.
Review ampacity, voltage drop, breaker suggestion, and graph results.
Use the CSV or PDF buttons to export the calculated summary.

Frequently Asked Questions

1. What does this calculator actually size?

It estimates a practical cable cross-sectional area using load current, installation derating, voltage drop, and a safety margin. It then maps the result to a standard cable size.

2. Why are power factor and efficiency included?

Motors and many real loads draw more current than ideal power alone suggests. Power factor and efficiency help convert input power into a more realistic current value.

3. Why can voltage drop force a larger cable?

A cable may carry current safely but still lose too much voltage over distance. Increasing conductor area reduces resistance and keeps terminal voltage within acceptable limits.

4. What is the grouping factor?

Grouping factor accounts for nearby loaded cables heating each other. More grouped circuits usually reduce usable ampacity, so larger cables may be required.

5. Is the recommended breaker always final?

No. It is a practical starting point. Final breaker selection should also consider short-circuit level, protective coordination, inrush behavior, and applicable electrical codes.

6. Can I use aluminum instead of copper?

Yes, but aluminum usually needs a larger cross-section for the same duty. It also has different installation, termination, and corrosion considerations.

7. Does this replace code compliance checks?

No. It helps with engineering estimation and comparison. Always verify the result against local standards, equipment ratings, manufacturer tables, and project specifications.

8. Why is my selected cable larger than expected?

Long routes, hot ambient conditions, grouped circuits, low allowable voltage drop, or motor starting requirements can all push the selection upward.