24V Voltage Drop Calculator | Cable Loss and Terminal Voltage

Calculator Inputs

System Voltage (V)

Load Current (A)

One-way Length

Length Unit

Conductor Material

Conductor Temperature (°C)

Cable Size Input

Cable Area (mm²)

AWG Size

Parallel Conductors Per Polarity

Return Path Model

Extra Loop Resistance (mΩ)

Target Maximum Drop (%)

Example Data Table

Current (A)	One-way Length (m)	Size (mm²)	Material	Total Resistance (Ω)	Voltage Drop (V)	Terminal Voltage (V)	Drop (%)
5.00	5.00	2.50	Copper	0.071670	0.3584	23.6416	1.493
10.00	10.00	4.00	Copper	0.089588	0.8959	23.1041	3.733
15.00	20.00	10.00	Copper	0.071670	1.0751	22.9249	4.479
8.00	15.00	6.00	Aluminum	0.146994	1.1760	22.8240	4.900

These examples assume a 24V DC system, 30°C conductor temperature, one parallel run, and a dedicated return conductor.

Formula Used

1) Cable resistance at 20°C
R₂₀ = ρ × L / A

2) Temperature-adjusted resistance
R_T = R₂₀ × [1 + α × (T - 20)]

3) Voltage drop
V_drop = I × R_total

4) Power loss
P_loss = I² × R_total

5) Terminal voltage
V_terminal = V_source - V_drop

6) Required conductor area for a target drop
A = (ρ × L × I) / V_allowed

In these formulas, ρ is resistivity, L is total conductor length, A is conductor area, α is temperature coefficient, T is conductor temperature, and I is current.

How to Use This Calculator

Enter the load current and one-way cable length.
Select meters or feet, then choose copper or aluminum.
Set the conductor temperature for a realistic resistance estimate.
Pick cable size in mm² or AWG, then add parallel runs if used.
Select the return path model and include connector resistance if known.
Enter your allowed drop percentage and press the calculate button.
Review voltage drop, terminal voltage, efficiency, and recommended conductor size.
Use the CSV or PDF buttons to save the calculation summary.

Frequently Asked Questions

1) Why is voltage drop important in a 24V system?

Low-voltage systems lose a larger share of supply voltage across cables. Even a small resistance can reduce terminal voltage, cause dim lights, weak motors, controller faults, and wasted power.

2) Why does the calculator use one-way length?

Installers usually measure the route in one direction. The calculator then applies the selected return-path model to estimate the full current loop length automatically.

3) Does temperature really change voltage drop?

Yes. Resistance increases as conductor temperature rises. Warm cables drop more voltage than cool cables, so temperature correction helps avoid undersized wiring in demanding conditions.

4) Should I choose copper or aluminum?

Copper has lower resistivity and usually needs less cross-sectional area for the same drop. Aluminum can still work, but it often requires a larger conductor and careful terminations.

5) What is extra loop resistance?

It models added resistance from connectors, fuse holders, switches, terminals, busbars, or aging contacts. Adding it makes the result more realistic for complete installed circuits.

6) What drop percentage is normally acceptable?

Many designers target 2% to 3% for sensitive loads and short feeder runs. Motors or noncritical loads may tolerate more, but lower drop generally improves performance.

7) Why does parallel wiring reduce voltage drop?

Parallel conductors increase effective cross-sectional area. More area lowers resistance, which lowers voltage drop and heating for the same current and route length.

8) Can I use this for battery-powered equipment?

Yes. It is especially useful for battery banks, vehicles, solar storage, telecom loads, and control panels where 24V DC cable losses strongly affect delivered voltage.