Voltage Drop Calculator

Calculate Voltage Drop, Wire Size, Cable Length & Compliance

🔌 Voltage (V)

⚡ Current (A)

📏 Cable Length (meters)

📐 Wire Size (mm²)

🧪 Conductor Material

⚡ System Type

💡 Voltage Drop Formula: VD = (√3 × I × L × R) / 1000 (3-phase) | VD = (2 × I × L × R) / 1000 (single-phase)

VD = I × R × L × (1 or √3) / 1000 | %VD = (VD / V) × 100

📖 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

📊 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

Standard	Max Voltage Drop	Application
NEC (USA)	3% (branch), 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

❓ Frequently Asked Questions

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.

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 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.