Voltage drop helper
Voltage Drop Percent Calculator
Convert between dropped volts and percent voltage drop for feeder, branch-circuit, and DC run documentation.
Convert Voltage Drop Percent
Translate between dropped volts and percent voltage drop when the nominal circuit voltage is already known.
Result
Voltage drop
3.00%
Result notes. Keep inputs, assumptions, and result together before using this value in project records.
Keep the entered values, assumptions, and result together when adding this calculation to job notes or submittal records. Final installation choices should align with the applicable code edition, equipment listing, manufacturer instructions, local amendments, and AHJ requirements.
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Single-phase and three-phase voltage-drop checks for feeders and branch circuits using run length, conductor resistance, and load current.
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Formula and field context
Convert between dropped volts and percent voltage drop for feeder, branch-circuit, and DC run documentation.
Formula context
Voltage Drop Chart
Voltage drop is a design-performance check, not a simple wire-size lookup. A 3% target equals 3.6 V on a 120 V circuit, 7.2 V on 240 V, and 14.4 V on 480 V; a 5% target equals 6.0 V, 12.0 V, and 24.0 V. After choosing the target, use the calculator with one-way distance, actual load current, conductor material, conductor size, and phase before changing a conductor size.
Formula
Single phase: Vdrop = 2 x K x I x D / cmil. Three phase: Vdrop = 1.732 x K x I x D / cmil.Variables to keep with the result
- K is the conductor material constant used by the calculator.
- I is the expected load current, not automatically the breaker rating.
- D is one-way circuit distance including real route length.
- cmil is conductor area in circular mils.
Formula and variables
Voltage drop percent equals dropped volts divided by nominal voltage, multiplied by 100. The reverse calculation multiplies nominal voltage by the allowed percent drop. Always keep the voltage base with the result because 3% of 120 V is not the same number of volts as 3% of 480 V.
Field example
If a 240 V circuit drops 7.2 V, the drop is 3%. If a 480 V feeder has a 2% planning limit, that limit equals 9.6 V. The conversion is helpful after a measurement, estimate, or drawing note already provides either dropped volts or a percent target.
When to use the full calculator
Use the full voltage-drop calculator when conductor material, length, load current, phase, and conductor size must be considered. This conversion does not choose wire size or approve a design.