How Voltage Drop Works
Voltage drop occurs when the voltage at the end of a run of cable is lower than at the beginning. Any length of wire has some electrical resistance, and when current flows through it, that resistance causes a drop in voltage, similar to pressure loss in a water pipe.
Four Major Causes of Voltage Drop:
- Material Resistance: Copper is a better conductor than aluminum, resulting in less drop.
- Wire Size: Thicker wires (lower AWG) have less resistance.
- Cable Length: The longer the wire, the greater the resistance and voltage drop.
- Current Load: The more amps flowing through the wire, the more voltage is lost.
Voltage Drop Calculation Formula
The basic Ohm's law formula used is V = I × Z.
- Single Phase: VD = (2 × K × I × L) / CM
- Three Phase: VD = (1.732 × K × I × L) / CM
- *Where K is material resistivity, I is current, L is length, and CM is circular mils.
Typical AWG Wire Sizes
| AWG Size | Cross Section (mm²) | Max Amps (Typ. NEC) |
|---|---|---|
| 14 AWG | 2.08 | 15 A |
| 12 AWG | 3.31 | 20 A |
| 10 AWG | 5.26 | 30 A |
| 8 AWG | 8.37 | 40 A |
| 6 AWG | 13.30 | 55 A |