FREE ENGINEERING CALCULATOR

Solar Voltage Drop & Conductor Loss Calculator

Calculate DC string & AC voltage drop, power loss in Watts, and verify NEC 210.19 / NEC 690 3% maximum drop limits for residential & commercial solar permit sets.

📥 Circuit Parameters

Circuit System Type

Nominal Circuit Voltage (Volts)

Circuit Operating Current (Amps)

One-Way Conductor Length (Feet)

Conductor Material

Wire Size (AWG / kcmil)

📊 Engineering Results

Voltage Drop (Volts) —

Voltage Drop Percentage —

End-of-Run Voltage —

Conductor Power Loss —

NEC 210.19 Compliance (< 3%) —

Conductor Resistance (R) —

Annual Energy Loss Est. (5 hrs/day) —

Engineering Calculation Formulas

Single-Phase / DC Circuits: V_drop = (2 × K × I × L) / Circular_Mils Three-Phase Circuits: V_drop = (√3 × K × I × L) / Circular_Mils

Where: K = 12.9 for Copper, 21.2 for Aluminum; I = circuit current in Amps; L = one-way length in feet; Circular Mils = conductor area per NEC Chapter 9, Table 8.

Conductor Power Loss: P_loss (Watts) = I² × R_conductor = V_drop × I Voltage Drop Percentage: % Drop = (V_drop / V_nominal) × 100

NEC Code Rule: The National Electrical Code (NEC 210.19(A) Informational Note 4 & NEC 690) recommends that voltage drop on branch circuits does not exceed 2% for solar PV (to prevent inverter overvoltage trips on 240V/480V lines) and a maximum of 3% for branch circuits / 5% overall.

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