Doug gets the prize. It is not a part 1 code rule it is a part 2 code rule. Part 2? Electricians install electrical products to the part 1 standard. Code book! So what code does a manufacturer use? They use Part 2. Part 2 has hundreds of code books. One such standard is the installation of underground systems, Another might be the C22.2 N0. 18 OUTLET BOXES, CONDUIT BOXES, AND FITTINGS where we might learn about sectional boxes and how they are to be made.
So the sectional boxes are attached together with a screw that is not tested for bonding continuity between sections so when field assembled the EC must ensure bonding continuity between sections.