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Estimate conductor voltage drop with the approximate K-method (Table 8) or the exact R/X method (Table 9), then check it against the NEC's recommended 3% branch / 3% feeder / 5% combined guidance.
Estimate conductor voltage drop with the approximate K-method (Table 8) or the exact R/X method (Table 9), then check it against the NEC's recommended 3% branch / 3% feeder / 5% combined guidance.
Electrical systems sized incorrectly can cause fire, explosion, electrocution, or carbon monoxide poisoning. Results are estimates only and must be reviewed by a licensed professional before any work is performed. Do not install based on these results alone. Read full terms.
NEC 210.19(A) and 215.2(A) informational notes recommend a maximum 3% voltage drop on branch circuits and 5% combined on feeder + branch — they are recommendations, not mandates, but most AHJs enforce them.
Use Vd = 2 × K × I × D / CM for single-phase (×√3 for three-phase), where K is conductor resistivity (12.9 copper / 21.2 aluminum), I is load current in amps, D is one-way distance in feet, and CM is conductor circular mils. Increase wire size whenever the result exceeds 3% on a branch circuit.
Yes — NEC 250.122(B) requires the equipment grounding conductor to be increased proportionally when the ungrounded conductors are upsized for voltage drop, so the EGC maintains its fault-clearing capacity.