For a feeder supplying household cooking equipment and electric clothes dryers, how is the maximum unbalanced load on the neutral conductor defined?

The maximum unbalanced load on the neutral conductor for a feeder supplying household cooking equipment and electric clothes dryers is defined as 70% of the load on the ungrounded conductors. This percentage is established based on the considerations of how these appliances operate and the expected current flow.

In a system where both a cooking appliance and dryer might operate simultaneously, their loads can be unevenly distributed across the phases. The 70% rule accounts for the fact that while individual loads might be significant and constant, the actual current returning through the neutral can be substantially less, especially when considering the nature of current draw and phase balancing in a typical residential setting. This limits the amount of current that the neutral conductor will have to carry and allows for some margin of safety and efficiency in the system.

By defining the maximum unbalanced load at 70%, the code recognizes the operational characteristics of these appliances and strives to ensure both safety and functionality in residential electrical systems. The consideration of maximum unbalanced loads is crucial in preventing overheating and maintaining the integrity of the electrical installation.