Understanding Voltage Drop Guidelines
All electrical conductors have internal resistance. As electrical current travels through a wire, some of the voltage is lost as heat due to this resistance. The longer the wire, the greater the drop. If the voltage drops too low, electrical equipment will draw more current to compensate, leading to overheating, inefficiencies, and potential equipment failure.
National Electrical Code (NEC) Recommendations
The NEC strongly recommends keeping voltage drop within safe limits to maintain equipment longevity:
- Branch Circuits: No more than a 3% voltage drop.
- Total System (Feeder + Branch): No more than a 5% total voltage drop.
The Calculation Formula
This calculator utilizes standard industry formulas. For Single Phase or DC circuits, the formula is VD = (2 × K × I × D) ÷ CM. For Three Phase circuits, we use VD = (1.732 × K × I × D) ÷ CM.
- K: Direct current constant representing ohms per mil foot (12.9 for Copper, 21.2 for Aluminum).
- I: Current load in Amps.
- D: One-way distance in feet.
- CM: Circular Mils of the wire gauge selected.