300.15(F) Fitting.
Code Change Summary: Revised code language on concealing fittings.
There are many listed transition fittings that work as an extension of a raceway. Transitioning from flexible metal conduit (FMC) to electrical metallic tubing (EMT) is one example (see image).
In the 2017 NEC®, using a listed FMC to EMT fitting was a code violation unless the fitting was accessible after installation. It may have been ok to install such a fitting above a suspended grid ceiling where removal of a ceiling tile could grant access to the fitting but to use the same fitting inside a finished wall would violate Section 300.15(F).
In order to pass inspection, some electricians have had to resort to installing access panels to grant access above hard lid ceilings where these fittings were used.
In the 2020 NEC®, a public input (code change proposal) was accepted to allow such fittings to be concealed if they are listed for concealment.
Below is a preview of the NEC®. See the actual NEC® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the 2020 NEC® edition of NFPA 70.
2017 Code Language:
300.15(F) Fitting. A fitting identified for the use shall be permitted in lieu of a box or conduit body where conductors are not spliced or terminated within the fitting. The fitting shall be accessible after installation.
2020 Code Language:
300.15(F) Fitting. A fitting identified for the use shall be permitted in lieu of a box or conduit body where conductors are not spliced or terminated within the fitting. The fitting shall be accessible after installation, unless listed for concealed installation.