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

The maximum allowable voltage drop for feeder conductors, as stipulated by the National Electrical Code (NEC), is set at 5% for feeders and branch circuits combined. This standard helps ensure efficient operation of electrical systems, as excessive voltage drop can lead to reduced performance of electrical equipment and potential overheating.

In practical terms, this means that when designing and installing circuits, the total voltage drop from the service entrance to the farthest load should not exceed 5%. This figure is often broken down where a maximum of 3% is permitted for branch circuits, which operates under the premise that branch wiring should maintain voltage levels strictly at the point of use. However, when considering feeder conductors, the combined limit allows for a more flexible design while still maintaining overall system efficiency.

This 5% rule of thumb is an essential guideline in electrical design to help mitigate issues arising from high voltage drops, such as flickering lights, inefficiencies, and electrical component failure, ensuring reliability and safety in electrical systems.