To maintain accessibility of connections inside an outlet box, the NEC permits a surface extension to be made by installing ___.

The correct choice regarding maintaining accessibility of connections inside an outlet box is the installation of an extension ring. An extension ring serves to provide additional space for wiring and makes connections more accessible by allowing devices or fixtures to be mounted more securely without compromising the ability to access the wires inside the junction box.

When using an extension ring, it ensures that the outlet box remains accessible according to the National Electrical Code (NEC) requirements. The NEC emphasizes that boxes must have enough volume and space to accommodate wiring devices, ensuring safety and functionality in electrical installations. Therefore, utilizing an extension ring not only satisfies the NEC’s accessibility mandate but also provides a neat and professional installation.

While other options may appear relevant on first glance, they do not align with the specific requirement of maintaining direct accessibility for connections in outlet boxes. An external box could complicate access by creating unnecessary boundaries, and conduit fittings, while useful for conduit connections, don’t offer the depth or accessibility that an extension ring does. A wiring harness focuses on organization but doesn’t address the need for direct access to simplified wiring inside the outlet box.