Voltage Drop and Wire Size Guide
Why Voltage Drop Matters
Voltage drop is the loss of voltage along a conductor. It rises when current is high. It also rises when the circuit is long. A large drop can make equipment run hot. Motors may start poorly. Lights may dim. Electronics may act in unstable ways. Good wire sizing keeps the delivered voltage close to the source voltage.
What This Tool Checks
This calculator estimates drop for DC, single-phase AC, and three-phase AC circuits. It handles copper, aluminum, and custom conductors. It also accepts temperature, power factor, conductor reactance, and parallel runs. These options help with feeder studies, branch circuits, solar battery runs, control panels, and long outdoor circuits.
How Wire Size Changes the Result
Smaller conductors have more resistance. More resistance creates more drop and more heat. Larger conductors reduce resistance. They also improve efficiency. The suggested size is based on the target voltage drop. It does not replace ampacity rules. Always compare the result with local code, insulation rating, terminal rating, and installation method.
Material and Temperature Effects
Copper has lower resistivity than aluminum. So copper usually gives less drop at the same area. Aluminum can still be a good choice for large feeders. Temperature also matters. A hot conductor has higher resistance. The calculator adjusts resistance with a temperature coefficient. This gives a more realistic estimate than a cold conductor value.
AC Power Factor and Reactance
AC voltage drop depends on resistance and reactance. Power factor changes the active part of the drop. Low power factor can increase the effect of reactance. This is important for motors, transformers, and inductive loads. For short branch circuits, reactance may be small. For long feeders, it can become useful.
Using Results Safely
Use the result as a design estimate. Check the drop percent first. Then compare receiving voltage, losses, and suggested wire size. Export the CSV or PDF for records. A final design should still include protective devices, short-circuit checks, grounding, ambient correction, conduit fill, and code review.