What is the maximum allowable voltage drop for feeders according to the NEC?

The maximum allowable voltage drop for feeders according to the National Electrical Code (NEC) is typically 3%. This percentage is set to ensure that electrical equipment operates efficiently and safely. A voltage drop greater than this can lead to inadequate voltage at the point of use, which can impact the performance of electrical devices, causing them to operate less efficiently, become damaged, or even fail.

The reasoning behind the 3% guideline is based on balancing the efficiency of the electrical system with the cost of oversized conductors. If the voltage drop is too high, it can result in increased power losses, which is not only inefficient but can also lead to increased energy costs. The NEC aims to maintain a standard that provides reliable power delivery while also being economically feasible.

While lower percentages like 1% and 2% may be suggested for branch circuits and lighting loads to maintain even tighter control on voltage levels, the established threshold for feeders is 3%. This allows for some flexibility while still ensuring that voltage drop does not significantly affect the performance of electrical systems.