This simulator runs a 120 V circuit out to a load and shows what the wire costs you. Pick the conductor material and size, stretch the run, and raise the load current; the wire fades from source to load as voltage is lost along it, and the load voltage and percent drop update instantly. A banner compares the result with the NEC's informational 3 percent branch-circuit and 5 percent feeder-plus-branch recommendations.
• An animated conductor from a source panel (120 V) to a load, with a neutral return line, a label for the chosen conductor, and a marker showing the voltage drop in volts and percent. • A copper/aluminum switch, an AWG selector with ten sizes, a one-way length slider (10-500 ft) and a load-current slider (1-200 A). • Readout tiles for source voltage, load voltage, percent drop and conductor. • A limit banner that turns green, amber or red as the drop crosses 3 and 5 percent, plus notes, formulas and a worked example.
Voltage drop is K × I × 2L ÷ CM, where K is the resistivity constant of the metal (12.9 ohm-cmil per foot for copper, 21.2 for aluminum), I is the load current, L is the one-way length in feet and CM is the conductor's area in circular mils. The factor of 2 counts the trip out and back. A 20 A load on 100 ft of #12 copper drops about 7.9 V, which is roughly 6.6 percent of 120 V.
Drop rises directly with current and length and falls as conductor area grows, so the usual fixes are a larger conductor, a shorter run or a higher-voltage circuit. Aluminum has only about 64 percent of copper's conductivity, so it must be sized larger for the same drop. This model uses a fixed 120 V single-phase source and DC-style resistance, so it does not include reactance, temperature correction or three-phase √3 factors.
Voltage drop equals K times current times twice the one-way length, divided by the conductor's circular-mil area. K is 12.9 for copper and 21.2 for aluminum. The doubling accounts for current flowing out on one conductor and back on the other.
The NEC gives informational recommendations rather than mandatory limits: about 3 percent for a branch circuit and about 5 percent combined for feeder plus branch circuit. The simulator's banner turns amber above 3 percent and red above 5 percent of the 120 V source.
Aluminum conducts about 64 percent as well as copper for the same cross-section, so its resistance per foot is higher. To get the same voltage drop you must step up to a larger conductor. Switch the material button with everything else fixed and watch the drop jump.
No. It uses a simple resistive calculation at a fixed 120 V. Real designs also consider conductor temperature, reactance on larger sizes and three-phase or 240 V systems. Use it to understand how size, length, current and material interact.