Voltage Drop Guide
A comprehensive engineering reference covering key concepts, formulas, standards, and best practices.
What Is This Calculator For?
Voltage drop is the reduction in electrical potential along a conductor due to its resistance. Excessive drop causes equipment malfunction and energy waste.
Key Input Parameters Explained
The accuracy depends on quality of inputs. Below are the key parameters.
| Parameter | Symbol | Typical Range | Notes |
|---|---|---|---|
| Current (I) | I | 1–5000 A | Load current ×1.25 |
| Length (L) | L | 1–5000 m | One-way distance |
| Conductor Size | mm² | 0.5–500 | Cross-sectional area |
| Voltage (V) | V | 12–1000 V | System voltage |
Formulas & Calculation Methods
Single-phase: V_drop = 2 × I × L × R_per_m
Three-phase: V_drop = √3 × I × L × R_per_m
Percent: V_drop% = (V_drop / V) × 100
Common Mistakes
- Using one-way length (use circuit length = 2×L)
- Forgetting √3 for three-phase
- Using nominal current without 125% NEC continuous factor
- Ignoring temperature correction (0.4%/°C above 25°C)
Applicable Standards
NEC 210.19 FPN No.4, IEC 60364-5-52, IEEE 141
Frequently Asked Questions
Max voltage drop per NEC?
3% branch, 5% total (feeder+branch) per NEC 210.19.
How to reduce without upsizing?
Increase system voltage, use parallel conductors, or switch to copper.
Why critical for 12V?
1V drop is 8.3% at 12V vs 0.8% at 120V. Low-voltage systems need proportionally larger wire.