cables calculator

What this cables calculator helps you estimate

This calculator gives a practical estimate for electrical cable sizing using two common checks: ampacity (how much current a cable can safely carry) and voltage drop (how much voltage is lost over distance). It then recommends the smallest standard cable size that satisfies both.

Inputs explained

1) System type

Voltage drop behaves differently in DC/single-phase versus three-phase systems. The calculator automatically applies the proper multiplier in each case.

2) Conductor material

Copper has lower resistance than aluminum, so it usually allows smaller cross-sectional area for the same performance. Aluminum may still be cost-effective for long runs and larger feeders.

3) Length, current, and voltage

• Length: enter one-way route length in meters.
• Current: expected load current in amperes.
• Voltage: nominal supply voltage at source.

How the calculation works

The calculator first computes the area required to meet the allowed voltage drop using:

• DC / single-phase: Vdrop = (2 × I × L × ρ) / A
• Three-phase: Vdrop = (√3 × I × L × ρ) / A

Then it checks current carrying capacity with a simple temperature derating model and selects the first standard size that passes both criteria.

Why voltage drop matters

Excessive voltage drop can lead to poor motor starting, dim lights, higher losses, and unstable operation for sensitive electronics. Even if a cable is thermally safe, it may still perform poorly if voltage drop is too high.

Good practice before final design

• Verify your local electrical code requirements.
• Check insulation type, installation method, grouping, and conduit fill.
• Confirm short-circuit withstand and protective device coordination.
• For critical systems, have calculations reviewed by a licensed electrician/engineer.

Quick interpretation guide

If your recommended size seems large, reduce the run length (if possible), raise the system voltage, or allow a slightly higher drop within code limits. If no size is found, the load may be too high for a single run, and parallel conductors or a different design approach may be needed.