Maximum Wire Length Calculator - Voltage Drop and Cable Length Tool
Calculate maximum cable length for DC, single-phase, two-phase, and three-phase systems while respecting voltage drop limits and insulation temperature ratings. Supports copper/aluminum, parallel conductors, and IEC 60364 & NEC Article 215 compliance.
When You Need This Calculation
- Determining how far a 24V DC solar panel can be from its charge controller
- Sizing feeders for a 480V three-phase motor located 500 m from the main panel
- Verifying if a 230V lighting circuit can extend to the end of a long corridor without flickering
- Designing low-voltage DC distribution in a data center with strict efficiency targets
- Checking if existing wiring can support a new high-power load without exceeding temperature ratings
How Maximum Length Is Determined
The tool solves the inverse of Ohm's Law:
L_max = (V_drop × A) / (ρ × I × N)Where:
- L_max: Maximum allowable length (m)
- V_drop: Allowable voltage drop (V)
- A: Conductor cross-sectional area (mm²)
- ρ: Resistivity at operating temperature (Ω·mm²/m)
- I: Load current (A)
- N: Number of parallel conductors
Note: For AC systems, the formula includes power factor and phase configuration.
Temperature & Insulation Rating
Conductor temperature affects both resistance and insulation life. This calculator uses temperature-corrected resistivity based on:
| Insulation Type | IEC/CEI | NEC | Typical Applications |
|---|---|---|---|
| PVC | 70°C | 60–75°C | General wiring, indoor circuits |
| XLPE/EPR | 90°C | 90°C | Outdoor, buried, industrial |
| Mineral Insulated | 105°C | 90°C | High-temperature environments, fire-rated |
| THHN/XHHW | 90°C | 75–90°C | Commercial buildings, wet locations |
Industry-Specific Applications
| Field | Use Case | Why It Matters |
|---|---|---|
| Solar PV | String-to-combiner box distance | Excessive drop reduces system efficiency and MPPT performance |
| Industrial Motors | Feeder from panel to motor | Low voltage causes torque reduction and overheating |
| Lighting Systems | Long runs in corridors or tunnels | 3% max drop ensures consistent brightness and lamp life |
| Data Centers | DC power distribution units (PDUs) | Efficiency loss directly impacts PUE and cooling load |
| EV Charging | From transformer to charging station | High currents require careful length planning to avoid voltage sag |
Reference Standards
- IEC 60364: Electrical installations in buildings — limits voltage drop to 3% for lighting, 5% for motors
- NEC Article 215: Requires voltage drop not exceed 3% for branch circuits, 5% total from source to outlet
- IEEE 141: Recommended practice for electric power distribution in industrial plants
- UL 486A/B: Wiring device standards including temperature ratings
Frequently Asked Questions
Why is cable length limited by temperature?
Conductors heat up under load. If temperature exceeds insulation rating (e.g., 70°C PVC), it can degrade over time. This calculator ensures both voltage drop and thermal safety are met.
Can I use this for underground cables?
Yes, but ensure you input the actual operating temperature. Underground cables may run hotter due to soil resistivity and lack of airflow.
What is the difference between % and V voltage drop?
Percentage drop is relative to supply voltage (e.g., 3% of 230V = 6.9V). Use % for general design; use V when specifying exact tolerance (e.g., motor starter requires ≤10V drop).
Does this support multi-core cables?
Yes—select 'Multipolar' or specific types like Tripolar, Quadrupolar, etc. The tool assumes all conductors are identical in size, material, and length.
