How are multiwire branch circuits required to operate in relation to loads?

Multiwire branch circuits are designed to supply one-to-neutral loads by utilizing two or more ungrounded conductors that share a single neutral conductor. This configuration enables the circuit to effectively balance the load across the ungrounded conductors while allowing the neutral conductor to carry the unbalanced current.

When loads are connected to a multiwire branch circuit that operates correctly, they should draw power from different phases (or poles) in a multi-phase system. By doing this, it helps minimize the amount of current flowing through the neutral, ensuring efficient operation and reducing the risk of overheating in the neutral conductor.

For example, in a standard residential setup where 120/240 volt service is provided, you'll typically have two 120 volt circuits that can share a neutral. If both circuits are evenly loaded with, say, a 15 amp load on each, the neutral will only carry the difference, which in this case could be zero if the loads are equal, thus optimizing safety and circuit performance.

This principle is crucial in ensuring compliance with the National Electrical Code, which mandates proper load distribution and proper use of neutral conductors in multiwire branch circuits.