Enter values
Formula and methodology
For DC and single-phase, estimated drop equals 2 × current × one-way length × corrected resistance. Three-phase uses √3 instead of 2. The model starts with NIST annealed-copper resistance at 20 °C and applies its stated temperature correction.
How to use the result
Check that each input uses the intended unit, then compare the displayed result with the assumptions above. Recalculate when the source values or operating conditions change. Do not use an estimate as a substitute for equipment documentation or professional review where safety depends on the result.
Reviewed sources
- Copper Wire Tables, NBS Handbook 100 — National Institute of Standards and Technology; reviewed September 1, 2026.
- NFPA 70, National Electrical Code — National Fire Protection Association; reviewed September 1, 2026.
Method reviewed September 1, 2026. Scheduled review by 2028-08-31.