Voltage Drop at 208V (Three-Phase AC)
208V is common in commercial 3-phase wye systems. It is often used for HVAC, kitchen equipment, and small motors.
Why 208V Systems Need Attention
At 208V, voltage drop matters on longer runs. A 3% drop on a 120V circuit is only 3.6V, but a load expecting 120V may run noticeably hotter or dimmer at 116V.
Example Calculation
For a 208V Three-Phase AC circuit at 40 A over 120 ft using 8 AWG copper:
Voltage drop = 1.732 x I x R = 1.732 x 40 x (ohms per ft for 8 AWG x 120 ft)
Common Applications at 208V
- Commercial HVAC
- Kitchen equipment
- Small 3-phase motors
Common Questions
What is the acceptable voltage drop for a 208V circuit?
Most engineers target 3% or less on branch circuits and 5% total (feeder plus branch). These are general guidelines, not hard NEC requirements. Check your local code.
What wire gauge should I use for a 208V circuit?
It depends on load current and run length. Use the voltage drop calculator with your specific values. A longer run or heavier load requires a larger gauge.
Does voltage drop affect safety?
Excessive voltage drop can cause motors to overheat, breakers to nuisance-trip, and equipment to malfunction. It is not just an efficiency issue.
Can I use aluminum wire on a 208V circuit?
Aluminum is commonly used for larger feeders (service entrances, subpanel feeds). For small branch circuits, copper is generally required. Aluminum has higher resistance than copper for the same gauge, so voltage drop is worse for the same wire size.