Wire Sizing Caveats: Ampacity, Drop, and Why Tables Lie to Beginners
Wire size calculators look definitive. In practice, ampacity tables, termination temperature limits, bundling, and voltage drop all interact. Here’s how our educational estimator thinks—and what it deliberately omits.
Two constraints, one conductor
A candidate AWG must carry the current (ampacity) and keep voltage drop under your planning target. Meeting one without the other is still a fail.
What our table sources mean
Ω/kft values are handbook-style educational resistances near room temperature. Aluminum is approximated as higher resistance than copper. These are not official NEC Chapter 9 reprints.
Safer DIY workflow
Estimate load amps
From watts÷volts or a clamp measurement when safe.
Check drop
Use the voltage-drop calculator for the proposed AWG and length.
Coordinate the breaker
Breaker, wire, and device must match—never upsize only the breaker.
Stop for permits
Permanent building wiring belongs with qualified professionals.