Verified Mathematical Model & Formulation
Single Phase / DC: VD = (2 × K × L × I) / Circular Mils Three Phase: VD = (1.732 × K × L × I) / Circular Mils Drop % = (VD / Source Voltage) × 100
Calculates the ohmic resistance loss across conductor length (L in feet) carrying current (I in amps). K is conductor resistivity constant (~12.9 for copper, ~21.2 for aluminum at 75°C).
Configurable Parameters & Standard Units
- Source Voltage (V): (Default: 120 v)
- Load Current (Amperes): (Default: 16 a)
- One-Way Distance (Feet): (Default: 100 ft)
- Conductor (1=Copper, 2=Aluminum): (Default: 1 count)
- Wire Size (14, 12, 10, 8, 6, 4, 2, 1/0): (Default: 12 count)
Standard Worked Example & Practical Verification
Scenario: Running a 20A 120V circuit over 150 feet using 12 AWG copper wire.
Practical Takeaway: Upsize conductor to 8 AWG or 10 AWG to maintain voltage drop below the recommended 3% limit (3.6V).
Frequently Asked Questions
What is the maximum acceptable voltage drop in building wiring?
The National Electrical Code (NEC Article 210.19) recommends that voltage drop should not exceed 3% for branch circuits, and total combined drop across feeder plus branch should not exceed 5%.
Why does excessive voltage drop damage equipment?
Under-voltage forces inductive electric motors and compressors to draw higher current to produce rated mechanical output, generating excessive internal heat that degrades windings and trips thermal breakers.