What this cable length calculator does
This calculator estimates the maximum one-way cable run length based on voltage drop limits. In practical terms, it helps you answer: “How far can I run this cable before voltage loss becomes too high?”
It works for low-voltage DC systems, single-phase circuits, and three-phase AC circuits. This is useful for solar installations, battery banks, LED lighting, pumps, motors, and remote equipment where cable runs are long.
How the calculation works
Cable voltage drop is driven by current, conductor resistance, and run distance. Resistance increases when:
- Current is higher,
- Cable area is smaller,
- Conductor material has higher resistivity (aluminum vs copper),
- Distance is longer.
Core relationship used
Lmax = (ΔV × A) / (I × ρ × k)
where:
ΔV = allowable voltage drop (V), A = cable area (mm²), I = current (A),
ρ = resistivity constant (Ω·mm²/m), k = circuit factor (2 for 2-wire, 1.732 for 3-phase).
Input guide
1) System Voltage
Enter nominal supply voltage (for example 12V, 24V, 48V, 120V, 230V, 400V).
2) Load Current
Use expected operating current, not peak surge current, unless you are designing specifically for startup conditions.
3) Allowable Voltage Drop
A common target is 3%. Sensitive electronics may need lower drop. Long feeder runs can sometimes tolerate more.
4) Material and Cable Area
Copper has lower resistance than aluminum. Increasing cable cross-sectional area (mm²) significantly reduces voltage drop.
Example scenario
Suppose you have a 24V system at 15A, a 3% drop target, copper conductor, and 4mm² cable in a 2-wire circuit. The tool computes your maximum one-way run and gives a recommended conservative run after applying your design margin.
Best practices for real projects
- Include a safety margin (this calculator supports that directly).
- Check local electrical code requirements for permitted voltage drop.
- Account for connector, terminal, and joint resistance in critical systems.
- Consider temperature effects, especially in hot environments.
- When in doubt, choose the next larger cable size.
FAQ
Is this “one-way” cable length or total conductor length?
The main result is one-way route length. For purchasing cable, total conductor length depends on how many conductors are used.
Can I use this for data or coax cables?
Not directly. Data and RF cables are governed by impedance, attenuation, and frequency-dependent behavior. This calculator is for power-cable voltage drop estimation.
Is this a substitute for engineering design?
No. It is an accurate planning tool, but final design should be verified against applicable standards and installation conditions.