Solid vs stranded wire: Gauge and length matter more than strand count

The resistance difference between solid and stranded copper wire of the same gauge is negligible at 60 Hz AC. What actually kills performance is using too-long or too-thin extensions — a 50-foot 14-gauge cord will drop noticeable voltage under a 15-amp load regardless. Stranded wire wins for flexibility and durability in extension cords; solid wire would crack from repeated coiling. Worry about length and gauge, not strand count.