What is the smallest 4" square metal box used for a split-wired receptacle when all incoming cables are #12 MC cables?

The correct choice indicates the use of a 1½ inch rise plaster ring as the smallest acceptable size for a square metal box used to accommodate a split-wired receptacle when all incoming cables are #12 MC cables.

A plaster ring serves a vital role in this scenario. It provides a means to extend the box to the finished wall surface, ensuring that the receptacle is securely mounted and that there is adequate space for the wiring connections. Additionally, when wiring with #12 MC cables, it’s essential to have sufficient space within the box to facilitate proper wire connections while maintaining compliance with electrical codes, which typically require a specific volume for wiring devices.

The 1½ inch height of the plaster ring strikes a balance, providing enough room for the split-wired receptacle and connections while remaining compact enough for a standard installation. Using a box that is either larger or smaller than the required dimensions can complicate the installation and potentially violate electrical box volume requirements.

In summary, the choice of a 1½ inch rise plaster ring is based on ensuring adequate space for connections and supporting the receptacle in a manner that meets safety and code standards. Other options either exceed the necessary size or do not meet the requirements for this specific application.