Table
Voltage Drop K-Factors for Copper and Aluminum
Voltage Drop K-Factors for Copper and Aluminum reference with assumptions and boundary notes.
Reference boundary
Preliminary voltage-drop resistance factor reference only. It does not set acceptable voltage drop, conductor ampacity, breaker size, or installation approval.
Reference table
Compare copper and aluminum K-factor values used in voltage-drop resistance estimates.
| Material | Conductor temp (C) | K factor (ohm-cmil/ft) | Resistivity (ohm mm2/m) | Use |
|---|---|---|---|---|
| Copper | 20 | 10.37 | 0.01724 | Base resistance temperature |
| Copper | 75 | 12.61 | 0.02097 | Temperature-adjusted voltage-drop resistance |
| Copper | 90 | 13.22 | 0.02198 | Temperature-adjusted voltage-drop resistance |
| Aluminum | 20 | 17 | 0.02826 | Base resistance temperature |
| Aluminum | 75 | 20.77 | 0.03453 | Temperature-adjusted voltage-drop resistance |
| Aluminum | 90 | 21.8 | 0.03624 | Temperature-adjusted voltage-drop resistance |
Use notes
- Use this table for preliminary reference and arithmetic checks only.
- Confirm equipment ratings, product markings, installation conditions, utility requirements, and the local authority requirements before design or field use.