Voltage Drop Calculator
Calculate voltage drop for copper and aluminum wire. NEC 210.19(A) and 215.2(A) compliance check (3% branch / 5% feeder+branch).
Circuit Parameters
Vdrop = (2 × L × I × R) / 1000 (single phase) | × √3 for three phase
Results
Voltage Drop
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% Drop
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NEC Compliance
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Voltage at Load
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Power Loss
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Min Wire Size
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How this was calculated
Resistance: Based on NEC Chapter 9, Table 8 conductor DC resistance at 75C. Actual AC resistance is slightly higher due to skin effect (significant above 2/0 AWG).
NEC limits: 3% for branch circuits (210.19(A) Informational Note), 5% total for feeder + branch (215.2(A) Informational Note). These are recommendations, not requirements.
Minimum wire: Smallest wire size that keeps voltage drop under 3%.
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Book a free strategy call →Understanding Voltage Drop
Voltage drop is the reduction in voltage as current flows through wire resistance. Excessive voltage drop causes motors to run hot, lights to dim, and electronic equipment to malfunction. The NEC recommends keeping branch circuit drops under 3% and total (feeder + branch) under 5%.
Key factors: longer distance increases drop linearly, heavier loads increase drop linearly, and larger wire gauge reduces drop. Aluminum wire has about 1.6x the resistance of copper, requiring upsizing. For three-phase circuits, the factor changes from 2 to sqrt(3) due to phase geometry.
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