Numbers convince engineers; pictures convince everyone else. Drag the sliders and watch the wire change color, the heat rise, and the bulb dim — the same NEC math as every calculator on this site, made visible.
The wire's color follows the NEC verdict: green within the 3% branch recommendation, amber between 3% and the 5% total budget, red beyond it. The bulb's brightness tracks delivered power — for a resistive load, output falls with the square of voltage, which is why a "small" 6% drop visibly dims it. The heat wisps scale with the watts burned in the conductor: that heat is your electricity bill leaving through the walls.
One honest distinction the colors preserve: a red wire from voltage drop means inefficiency and poor performance — not fire. Fire risk is ampacity, the separate NEC Table 310.16 limit, and the simulator flags that case with its own dashed OVERLOADED treatment so the two are never confused. Showing a client? Drag the distance slider out to their actual run and let the bulb make the argument for the thicker wire.
The bulb models a resistive load held at constant current — a fair illustration for heaters and incandescent lighting. Motors respond to low voltage by drawing more current (see the motor tool), and electronics hold power until they brown out, so real equipment is usually less forgiving than the picture, not more.
Red here means a failed voltage-drop check — wasteful and hard on equipment, but not a fire hazard by itself. The dashed OVERLOADED state is the dangerous one: current beyond the conductor's NEC Table 310.16 ampacity rating.
Resistive output scales with voltage squared: 94% voltage delivers about 88% power — and your eye is very good at noticing a 12% dimmer bulb. The physics is doing the persuading.
Yes — the simulator is freely embeddable with one iframe snippet. See the embed page for the code.