For feeder circuits with no motor loads, how is the overcurrent protective device sized?

The sizing of overcurrent protective devices for feeder circuits without motor loads requires consideration of the continuous and noncontinuous loads present. The correct approach is to size the overcurrent protective device at 125% of the continuous load plus 100% of any noncontinuous loads.

This method ensures that the circuit can handle continuous loads without tripping while also accommodating noncontinuous loads that may intermittently draw more current. Continuous loads are expected to run for three hours or more, while noncontinuous loads do not have this running duration requirement and can be more demanding at times. By applying the 125% rule to the continuous load, it provides a buffer to prevent nuisance tripping due to the prolonged nature of those loads.

As a result, this sizing strategy aims to achieve reliability and safety in the electrical system, accommodating variations in demand while also protecting the electrical infrastructure from potential overcurrents. Each component of the load is carefully considered to ensure that the protective device can manage the overall load characteristics effectively.