Voltage Drop Calculator | Wire Size, Cable Length, Current

📖 Voltage Drop Calculator

Voltage drop is the reduction in voltage along a circuit due to cable resistance. Excessive voltage drop can cause equipment malfunction, overheating, and energy loss. This tool calculates voltage drop, percentage, and recommends the correct wire size for single-phase and three-phase systems.

📐 Voltage Drop Formulas

Single Phase: VD = (2 × I × L × R) / 1000
Three Phase: VD = (√3 × I × L × R) / 1000
Voltage Drop %: %VD = (VD / V) × 100

Where:
VD = Voltage Drop (V) I = Current (A) L = Cable Length (m)
R = Resistance (Ω/km) - Copper: ~17.2 Ω/km, Aluminum: ~28.3 Ω/km

📊 Wire Resistance Values

Wire Size (mm²)	Copper (Ω/km)	Aluminum (Ω/km)
1.0	17.2	28.3
1.5	11.5	18.9
2.5	6.9	11.3
4.0	4.3	7.1
6.0	2.9	4.7
10	1.7	2.8
16	1.1	1.8
25	0.69	1.1
35	0.49	0.81
50	0.34	0.57

📌 Voltage Drop Standards (NEC & BS 7671)

Standard	Max Voltage Drop	Application
NEC (USA)	3% (branch circuits), 5% (total)	120V / 240V systems
BS 7671 (UK/India)	3% (lighting), 5% (power)	230V / 415V systems
IEC 60364	3% (lighting), 5% (power)	International standard

💡 Tips for Reducing Voltage Drop

Increase wire size (larger cross-section reduces resistance)
Shorten cable length where possible
Use copper instead of aluminum (lower resistance)
Use higher voltage (e.g., 415V instead of 230V)
Split load across multiple phases
Use parallel cables for very high current

🔧 How to Use This Calculator

Enter voltage - 230V (single phase) or 415V (three phase)
Enter current - load current in Amperes
Enter cable length - one-way length in meters
Select wire size - from 1.0mm² to 120mm²
Select material - Copper or Aluminum
Select system type - Single Phase or Three Phase
Results show voltage drop in volts, percentage, and compliance status

❓ Frequently Asked Questions (FAQ)

❓ What is voltage drop? ▼

Voltage drop is the reduction in voltage along a cable due to resistance. It causes equipment to receive less than the nominal voltage, affecting performance and efficiency.

❓ What is the acceptable voltage drop limit? ▼

NEC recommends 3% for branch circuits and 5% total. BS 7671 recommends 3% for lighting and 5% for power circuits. This calculator shows compliance with these standards.

❓ How to calculate voltage drop for single phase? ▼

Single phase voltage drop: VD = (2 × I × L × R) / 1000. The factor 2 accounts for the return path (live + neutral).

❓ How to calculate voltage drop for three phase? ▼

Three phase voltage drop: VD = (√3 × I × L × R) / 1000. The √3 factor accounts for the 120° phase difference.

❓ Does wire size affect voltage drop? ▼

Yes! Larger wire size (mm²) has lower resistance, which reduces voltage drop. Doubling the wire size roughly halves the voltage drop.

❓ Copper vs Aluminum - which is better? ▼

Copper has lower resistance (about 60% of aluminum) and better conductivity. Aluminum is lighter and cheaper but requires larger sizes for the same current.