Low Voltage Drop Calculator

Calculator Inputs

Circuit Type

Supply Voltage

Load Current

One-Way Cable Length

Length Unit

Conductor Material

Conductor Size Mode

Manual Area mm²

AWG Size

Conductor Temperature °C

Power Factor

Reactance Ω/km

Parallel Conductors Per Phase

Allowable Drop Percent

Custom Resistivity Ω mm²/m

Custom Temperature Coefficient

Example Data Table

System	Voltage	Current	Length	Material	Area	Typical Limit
DC	12 V	10 A	10 m	Copper	2.5 mm²	3%
Single Phase AC	230 V	18 A	35 m	Copper	4 mm²	3%
Three Phase AC	400 V	40 A	80 m	Aluminum	25 mm²	5%

Formula Used

DC voltage drop: Vd = 2 × I × L × R

Single phase AC voltage drop: Vd = 2 × I × L × (R × PF + X × sinθ)

Three phase AC voltage drop: Vd = √3 × I × L × (R × PF + X × sinθ)

Resistance from area: R/km = ρ × 1000 ÷ conductor area

Temperature correction: ρt = ρ20 × [1 + α × (T - 20)]

The calculator treats length as one-way distance. It adjusts resistance for conductor material, conductor size, operating temperature, and parallel runs.

How To Use This Calculator

Select DC, single phase AC, or three phase AC.
Enter the supply voltage and load current.
Add the one-way cable length and length unit.
Select conductor material and size method.
Enter temperature, power factor, and reactance when needed.
Set the allowed voltage drop percentage.
Press the calculate button to view results above the form.
Use CSV or PDF buttons to save the result.

Low Voltage Drop Planning Guide

Why Voltage Drop Matters

Low voltage systems need careful conductor planning. A small supply voltage leaves little room for loss. A 12 volt circuit can become weak after only a short run. Motors may start slowly. Lights may dim. Control devices may reset. The problem often appears after installation, when changes cost more. This calculator helps estimate the drop before cable is purchased.

Main Inputs

The key inputs are voltage, current, cable length, conductor material, and conductor size. Current has a strong effect because voltage drop rises directly with load current. Length also matters because a longer conductor adds more resistance. Smaller conductors create larger losses. Copper usually performs better than aluminum for the same area. Aluminum can still work well when sized correctly.

Advanced Electrical Factors

AC circuits may include resistance and reactance. Power factor changes how these values affect the drop. A three phase feeder uses a different multiplier than a single phase circuit. Temperature also matters. Conductors become more resistive when they heat up. This page adjusts resistivity with a temperature coefficient. That makes results more practical for real installations.

Reading The Results

The voltage drop value shows lost voltage in the cable. The percentage compares that loss with supply voltage. The load voltage shows the voltage remaining at the equipment. The loss value estimates heat wasted in the conductors. The status line compares the result with your selected limit. If the result fails, increase conductor area, reduce length, reduce current, or use parallel conductors.

Good Design Practice

Use this calculator as a planning aid. Always compare results with local electrical rules. Check insulation rating, installation method, ambient temperature, grouping, short circuit limits, and protective device requirements. Voltage drop is only one part of conductor selection. A safe design also needs correct ampacity, grounding, termination rating, and mechanical protection. For critical loads, add a safety margin.

FAQs

What is voltage drop?

Voltage drop is the voltage lost as current flows through a conductor. It happens because every conductor has resistance. In AC circuits, reactance may also affect the result.

Does cable length mean one-way length?

Yes. Enter the one-way distance from the source to the load. The calculator applies the correct circuit multiplier for DC, single phase, or three phase systems.

Why does low voltage drop matter more in 12 volt systems?

A small voltage loss is a larger percentage of a low supply voltage. A one volt loss is minor at 230 volts, but very large at 12 volts.

Can I use aluminum conductors?

Yes. Select aluminum from the material list. Aluminum has higher resistivity than copper, so it usually needs a larger cross sectional area for the same drop.

What is a good voltage drop limit?

Many designs target 3% for branch circuits and 5% for feeders. Local rules, equipment needs, and project specifications may require different limits.

Why is temperature included?

Conductor resistance increases when temperature rises. Including temperature gives a more realistic result for loaded cables, warm locations, and enclosed installations.

What does power factor change?

Power factor affects AC voltage drop when resistance and reactance are considered. It is mainly important for motors, transformers, and other inductive loads.

How can I reduce voltage drop?

Use a larger conductor, shorten the run, reduce current, improve power factor, increase supply voltage when allowed, or use parallel conductors where permitted.