What is the maximum number of disconnecting means required for a 240/120-volt three-wire feeder installed underground from a dwelling to a detached garage?

The correct answer is determined by the National Electrical Code (NEC), which sets guidelines for the installation of electrical systems, including the requirements for disconnecting means in feeder installations.

For a 240/120-volt three-wire feeder supplying a detached structure such as a garage from a dwelling, the NEC outlines that there must be a disconnecting means that is easily accessible and capable of disconnecting all ungrounded conductors of the feeder. Typically, when feeders are run to detached structures, it is common to provide a disconnecting means at both the originating location (the dwelling) and at the receiving location (the detached garage).

In situations where additional disconnecting means are allowed or necessary due to the length of the feeder, the specific requirements from the NEC indicate that more than one disconnecting means may be deployed, but it is typically not necessary to have a very high number like six or more unless dictated by unique conditions or configurations in the project.

The regulations prioritize safety and accessibility, ensuring that any person working on or around the feeder has a clear and rapid method to de-energize the circuits if needed. Thus, the requirement of having up to six disconnecting means can arise under certain extra conditions defined in the NEC.