Voltage Drop Calculator estimates voltage loss along electrical conductors based on load current, conductor size, material, length, and phase. It helps electrical and other MEP engineers size conductors for safe and efficient power delivery.
About voltage drop. Voltage drop is the reduction in electrical potential as current flows through a conductor. Excessive voltage drop can cause equipment malfunction, motor overheating, dim lighting, and increased energy losses. Most electrical codes (NEC, IEC) recommend keeping voltage drop below 3% for branch circuits and 5% for feeders.
About conductor size units. Conductor size can be specified in square millimeters (mm²), American Wire Gauge (AWG), or thousand circular mils (kcmil). mm² is standard in IEC-based regions, AWG is used in North America for smaller conductors, and kcmil is used for large conductors in Imperial contexts.
About conductor materials. Copper and aluminum are the most common conductor materials. Copper has lower resistivity (≈0.0172 Ω·mm²/m) than aluminum (≈0.0283 Ω·mm²/m), resulting in less voltage drop for the same cross-sectional area. Aluminum is lighter and cheaper but requires upsizing to achieve equivalent performance.
About phases. In single-phase systems, the current flows through one phase conductor and returns via the neutral, while in three-phase systems current is shared among three phase conductors. Three-phase circuits have lower voltage drop for the same load and conductor size because current is distributed.
Calculation. The tool supports two workflows:
Drop from Size: Given the system voltage (V), current (I), length (L), conductor material (copper/aluminum), phase (single/three), and size (mm², AWG, or kcmil), it calculates voltage drop (Vdrop), percent drop (%), and end voltage (Vend).
Size from Drop: Given the same parameters except conductor size, and with an allowable voltage drop (%), it calculates the minimum required conductor size (mm², nearest AWG, and equivalent kcmil).
The basic voltage drop equation is:
Vdrop = I × R, where R = ρ × k × L / A
— ρ is resistivity (Ω·mm²/m),
— k = 2 for single-phase or √3 for three-phase,
— A is conductor area (mm²).
- Example 1: 230 V, 16 A, 30 m, copper, 1φ, 2.5 mm² → Vdrop ≈ 5.3 V (2.3%).
- Example 2: 120 V, 20 A, 100 ft, copper, 1φ, 10 AWG → Vdrop ≈ 4.2 V (3.5%).
- Example 3: 400 V, 40 A, 50 m, aluminum, 3φ, target 3% → required ≈ 25 mm² (≈3 AWG).
Corresponding tools. To estimate electrical load before sizing conductors, use the Heating Load Calculator and Cooling Load Calculator. To size airflow and ducts for HVAC systems, use the CFM Calculator and Duct Sizing Calculator.
