Voltage Drop at 277V (Single-Phase AC)
277V is the phase-to-neutral voltage of a 480V 3-phase 4-wire system. It is common in commercial buildings for lighting circuits and some HVAC loads.
Why 277V Systems Need Attention
At 277V, voltage drop matters less on short runs but becomes significant over long feeders in large buildings or industrial plants.
Example Calculation
For a 277V Single-Phase AC circuit at 20 A over 150 ft using 12 AWG copper:
Voltage drop = 2 x I x R = 2 x 20 x (ohms per ft for 12 AWG x 150 ft)
Common Applications at 277V
- Commercial fluorescent/LED lighting
- HVAC controls
- Commercial building circuits
Common Questions
What is the acceptable voltage drop for a 277V 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 277V 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 277V 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.