The primary intent of this discussion is to explain how overcurrent protection devices are determined for single motor branch-circuits. References will be taken from the 2020 National Electrical Code (NEC). These references will apply to general single motor applications for a continuous duty NEMA Design B energy efficient motor, unless otherwise noted.
Feeders Part 3 Feeder Conductor Ampacity. The conditions of use must be considered when determining the minimum size of a feeder conductor. A continuous load, such as the lighting load in a store building, generates heat in the feeder conductor that must be compensated for. Ambient temperatures above 86oF or more than […]
The general rule in 215.3 is that a feeder overcurrent device shall have a rating not less than the noncontinuous load plus 125% of any continuous loads supplied by the feeder. Unless permitted for specific applications, such as motor circuits, the rating of the feeder overcurrent device is selected as […]
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