Definition
Voltage drop is the reduction in voltage between the source and the load caused by the resistance of the conductors carrying the current. Every wire has resistance, so some voltage is inevitably lost as heat along the run. The longer the cable and the thinner its gauge, the larger the drop and the less voltage actually reaches your equipment.
How much is acceptable
The U.S. National Electrical Code does not set a hard limit but recommends, in an informational note, keeping branch-circuit voltage drop at or below 3% and the combined feeder-plus-branch drop at or below 5%. For a single-phase circuit the drop is approximately Vd = 2 x I x R x L / 1000, where I is the load in amps, R is the conductor's ohms per 1,000 feet, and L is the one-way run length in feet; the factor of 2 accounts for the current traveling out and back. Three-phase circuits use 1.732 (the square root of 3) in place of 2.
Why miners should care
ASIC power supplies tolerate a voltage window, but excessive drop wastes energy as heat in the wiring and can pull the delivered voltage low enough to hurt efficiency or trigger under-voltage faults especially on long runs from a distant panel to a shed or container. Running 240V instead of 120V halves the current for the same power and roughly quarters the drop, which is a major reason serious mining circuits are wired at the higher voltage. When a far-flung site is involved, upsizing the conductor a step is cheap insurance against chronic voltage drop.
Plan conductor size against your load factor and total apparent power to keep drop within spec end to end.
In Simple Terms
Voltage drop is the reduction in voltage between the source and the load caused by the resistance of the conductors carrying the current. Every wire…