What NEC states for max. voltage drop?
The NEC states in an Informational Note that a maximum voltage drop of 3% for branch circuit conductors, and 5% for feeder and branch circuit conductors together, will provide reasonable efficiency of operation for general use circuits.For sensitive electronic loads, circuits should be designed for a maximum of 1.5% voltage drop for branch circuits at full load, and 2.5% voltage drop for feeder and branch circuits combined at full load.
Four practical approaches can be used to minimize voltage drop problems:
1. Increase the Number or Size of Conductors
Parallel or oversized conductors have lower resistance per unit length than the Code-required minimum-sized conductors, reducing voltage drop and increasing energy efficiency with lower losses than using the Code-required minimum-sized conductor.
In data centers and other sensitive installations,
it is not uncommon to find conductor gauges for phase, neutral, and
ground exceeding Code minimums, and a separate branch circuit installed
for each large or sensitive load.
To limit neutral-to-ground
voltage drop, install a separate, full-sized neutral conductor for each
phase conductor in single-phase branch circuit applications.For three-phase feeder circuits, do not downsize the grounded conductor or neutral. For three-phase circuits where significant non-linear loads are anticipated, it is recommended to install grounded or neutral conductors with at least double the ampacity of each phase conductor.
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