My usual practice when placing an outlet box (e.g., Raco 8232 quad
) near a service panel is to mount the box on the same backboard about an inch away from the panel. I then run the Romex cable through clamp connectors (e.g., Halex 3/8" no. 20511
) mounted in the knockouts in the panel and the box.
I recently came across a video
where rigid box spacers (e.g., Halex no. 91641
) were used between the panel and box. While this makes for a very neat installation, shielding the Romex cable from damage, one concern I would have is the lack of clamps preventing the movement of the cable when working in the panel or the box, notwithstanding the rigidity of the Romex. Of course, additional clamps (plastic, metallic) could be used in conjunction with the rigid box spacer, but that would make for one or two additional components in already tight quarters. I haven't tried this so it's not clear whether the back of the box would be flush with the backboard or is supported by the box spacers.
I welcome any comments including whether the code addresses this configuration (I was not able to find any provisions directly addressing the issue).