Voltage Drop in a Facility
It is expected and accepted (in the U.S.) that there will be a voltage drop of 3 to 5% from the point where the electric utility delivers power to the end user (usually at the meter) to the point within a facility where the electricity is finally consumed in an electrical device (the load). Unlike utility voltage levels which may be high or low, the voltage drop due to wiring impedance within a building will always drive voltage levels lower. For example, if the incoming utility voltage is 5% low, the voltage at the point of usage might be 8 to 10% (5%+3% to 5%+5%) below nominal due to the voltage drop within a building.
AC motors are commonly rated at 460V (480V-4%) rather than 480V to address the voltage drop in a facility – and to optimize motor performance.