Understanding Voltage Drop

Voltage drop happens because every wire has some resistance, and current flowing through that resistance uses up some voltage before it reaches the load. This calculator uses the formula: drop equals two times the one-way distance times the wire’s resistance per foot times the current.

Why It Matters

Excessive voltage drop can cause lights to dim, motors to run hot, and equipment to underperform. Electricians generally try to keep voltage drop under 3 percent for branch circuits.