Formula variables
- K is material resistivity in ohm mm2/m.
- I is load current in amperes.
- L is one-way length in metres.
- A is conductor area in mm2.
Assumptions
- Distance is one-way circuit length.
- The result uses conductor area and material resistivity as a preliminary estimate.
- The calculation does not check ampacity, conductor temperature rating, derating, short-circuit current, breaker sizing, or final code compliance.
- Confirm the actual system voltage, local authority requirements, utility rules, and product instructions before using results for design or installation.
Examples
Residential-style 240 V load. A 20 A load at 240 V over 30 m using copper 10 AWG estimates about 3.93 V drop, or 1.64 percent.
Commercial 600 V three-phase load. A 600 V three-phase load should use the line-to-line voltage when the load is connected line-to-line. Confirm the actual service and equipment voltage before calculating.