What is the point of that? I had understood that it could be closed in a wall.
Not that I was not surprised to learn that one could close it up.
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.
550.15(I) Boxes, Fittings, and Cabinets. Boxes, fittings, and cabinets shall be securely fastened in place and shall be supported from a structural member of the home, either directly or by using a substantial brace.
Exception: Snap-in-type boxes. Boxes provided with special wall or ceiling brackets and wiring devices with integral enclosures that securely fasten to walls or ceilings and are identified for the use shall be permitted without support from a structural member or brace. The testing and approval shall include the wall and ceiling construction systems for which the boxes and devices are intended to be used.
quote; as all the old houses around here used "real" 2"x4" studs with lath and plaster walls.
I worked in a Frank Lloyd Wright house which had 2" and 3" walls, He did not believe in wasting space for walls when it could be used for live in purposes.
What's inside the wall that is preventing the box from sitting flush and how proud does it sit from the wall? A picture of two would be very helpful. If the box is being obstructed by something inessential, like blocking or nailers on an interior wall, I would take a spade bit and drill out some of that material through the cutout for the box until it sits flush. Obviously, you wouldn't be able to do the same thing if the box was butting up against the exterior sheathing.
Also,It's interesting that those splices can be made in RV's and trailers and not homes. Why is this?
Many of the panelized homes also use connectors to join various sections together. No idea why they allow it there, but it would be nearly impossible to build it in a factory otherwise. Doing it on-site defeats some of the purpose of factory built. My guess is that the location and conditions of when they are used when built in a factory may be more well defined rather than random in a stick built house.
RVs and mobile homes are under a completely different set of codes than houses. Modular homes which come in sections are usually considered under the mobile home codes, (governed by the county building department in this area), much to the consternation of local building departments. For example, "houses" in this area require fire protection systems, but modular homes, which look exactly the same after they are finished, do not because mobile homes do not need them.
(1) Is fished between access points through concealed spaces in finished buildings or structures and supporting is impracticable.
(2) Is not more than 1.4 m (4½ ft) from the last point of cable support to the point of connection to a luminaire or other piece of electrical equipment and the cable and point of connection are within an accessible ceiling.