Voltage Drop Formula

Voltage Drop is created by internal resistance to the flow of electricity thought electric cable. It is the difference between the voltage at the beginning (source) of a cable run and that at its end. If the Voltage Drop is great enough, there will be a noticeable decrease in brightness of lamps along the cable. Maximum acceptable Voltage Drop is 1.3 to 1.5 Volts. If 60% or more of the fixtures are in the first half of the run, reduce the Voltage Drop figure by 16% or more of the fixtures are in the last half of the run, increase the Voltage Drop figure by 33%.