When calculating the total demand for a 3-phase feeder with both continuous and noncontinuous loads, what factor should be applied?

In calculating the total demand for a 3-phase feeder that includes both continuous and noncontinuous loads, the appropriate demand factor to apply to the continuous loads is 125%. This is in accordance with the National Electrical Code (NEC) that stipulates how to handle both types of loads when determining feeder sizing.

Continuous loads are defined as loads that are expected to run for three hours or more, whereas noncontinuous loads do not have such a time constraint. To ensure that the feeder is adequately sized to handle the continuous load without exceeding its rating, the NEC requires that you take 125% of the continuous load as part of your calculation. This adjustment is crucial for maintaining safety, preventing overheating, and ensuring reliable operation under load.

Applying the 125% factor allows for a margin of safety that anticipates possible fluctuations and provides for reliable performance. Noncontinuous loads can be taken at 100% of their demand, but the 125% factor specifically addresses the continuous loads, ensuring both the system's safety and functionality.