Cable Voltage Drop Calculator
Calculate voltage drop in long cable runs for efficient installations.
Voltage Drop Calculator
Ensure safe and efficient electrical systems
Results:
Voltage Drop (VD): 0.00 V
Percentage Voltage Drop (%VD): 0.00 %
How to Use the Calculator
Step-by-Step Guide
- Gather Details: Input Load Current (A), Cable Length (m), System Voltage (V).
- Select Cable Properties: Choose Conductor Material (Copper/Aluminum) and enter Cross-sectional Area (mm²).
- Specify Phase: Select Single-phase or Three-phase system.
- Calculate: Click "Calculate" to get Voltage Drop (VD) and Percentage Voltage Drop (%VD).
- Review Results: Check if %VD is within recommended limits (e.g., ≤ 3% for lighting, ≤ 5% for power circuits).
Conductor Resistivity
The calculator uses standard resistivity values:
- Copper: 0.0175 Ohm·mm²/m
- Aluminum: 0.0282 Ohm·mm²/m
These values are crucial for accurate voltage drop calculations.
Recommended Limits
Standard recommended voltage drop limits:
- Lighting Circuits: ≤ 3%
- Motor/Power Circuits: ≤ 5%
- Sensitive Systems (Data Centers, Solar Strings): ≤ 2%
Always refer to local electrical codes and standards.
How to Calculate Voltage Drop in Long Cable Runs – Step-by-Step Guide
When dealing with long cable runs—whether on industrial sites, commercial buildings, or solar farms—voltage drop becomes a serious concern. Excessive voltage drop leads to power loss, equipment underperformance, or even system failure.
As an Electrical Engineer with 10+ years of experience, I've used this calculation countless times to ensure safe and efficient installations.
Here’s a step-by-step guide to accurately calculate voltage drop and select the right cable size for long distances:
✅ Step 1: Gather Cable and Load Details
Before calculation, note down:
- Load Current (I) in Amperes (A)
- Cable Length (L) in meters (one-way)
- System Voltage (V)
- Phase type (Single-phase or Three-phase)
- Conductor material (Copper or Aluminum)
- Cross-sectional area (A) in mm²
- Resistivity (ρ) of conductor (Ohm·mm²/m)
Typical resistivity values:
- Copper: 0.0175 Ohm·mm²/m
- Aluminum: 0.0282 Ohm·mm²/m
✅ Step 5: Consider Derating and Site Conditions
Final cable selection should also consider:
- Grouping or bundling of cables
- Ambient temperature (≥40°C = derating)
- Soil conditions (for underground cables)
- Installation method (in air, duct, tray)
Use correction factors as per IEC 60364, NEC, or local standards.
Calculation Formulas
✅ Step 2: Use the Voltage Drop Formula
For Single Phase:
VD = (2 × ρ × I × L) / A
For Three Phase:
VD = (√3 × ρ × I × L) / A
Where:
- VD = Voltage Drop (in Volts)
- ρ = Resistivity of conductor
- L = One-way cable length
- A = Cross-sectional area of cable (mm²)
✅ Step 3: Calculate Percentage Voltage Drop
After calculating VD in volts:
🧮 Formula:
%VD = (VD / System Voltage) × 100
Standard recommended limits:
- ≤ 3% for lighting circuits
- ≤ 5% for motor/power circuits
- ≤ 2% in sensitive systems like data centers or solar strings
✅ Step 4: Example Calculation
Given:
Load Current: 100 A
Distance: 100 meters (one-way)
Voltage: 400V
Copper cable
Area: 35 mm²
Phase: Three-phase
Step-by-Step Calculation:
1. Use resistivity ρ = 0.0175
2. Apply three-phase formula:
VD = (√3 × 0.0175 × 100 × 100) / 35
VD ≈ (1.732 × 0.0175 × 10,000) / 35
VD ≈ 8.66 V
3. Calculate %VD:
%VD = (8.66 / 400) × 100 ≈ 2.17%
✔️ Result: The voltage drop is within limits — cable size is acceptable.
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