Can subpanel be mounted on the backside of the main panel wall?

Question

I'm wondering if it's against code to mount a subpanel directly on other side of the wall to the main panel. The main panel is surface mounted and I'm hoping the subpanel would be flush mounted.

Answer 1

I see no reason that would be a problem. They are different rooms (though the same room, often the same wall side-by-side, is fine too) so the main panel and the subpanel are each treated as a separate installation. Key things to keep in mind:

• Each panel needs a space in front of it 30" wide (panel does not need to be centered in this space) x 36" deep x 78" tall for working space. That is where two panels side-by-side can sometimes have an advantage.
• The usual subpanel rules apply - neutral and ground separate, no disconnect needed (though you can use a "main panel" as a subpanel if the price is right, as long as you separate neutral and ground).
• No ground rod needed for the subpanel because they are in the same building, even if the main panel is on an outside wall and the subpanel on an inside wall. The main panel should already have ground rod(s).
• Wire bending space might be an issue for the subpanel feed, particularly if your subpanel has a very large (e.g., 200A) feed. If it has a small feed (< 100A) then that is normally not a concern even back-to-back.
• Even if everything else is using cables, it may make sense to run conduit between the panels for (a) the feed and (b) moving circuits between panels.
• If you expect to move a bunch of circuits from the main panel to the subpanel then getting a compatible panel (brand (Square D, GE, Eaton, Siemens, etc.) and type (e.g., QO vs. Homeline or CH vs. BR) so that you can swap breakers between panels. But that is not a requirement in any way - the electrons don't care.