Wiring two sub panels together via panel lugs with one fed from main panel via circuit breaker

[ptavares]

Here's my scenario. Currently have a 100A sub properly installed, fed by a 50A breaker in the main that is connected to the sub lugs. I'd like to add a generator backfeed to the sub with properly interlocked breakers. To do this, I need to move the lug connection to a new 50 breaker in the sub, install my generator backfeed breaker (30A) right next to it, and add my interlock. This will eat up four of my breaker slots, leaving me only four left (can't use tandems as the remaining circuits (and others I'd like to be able to power with my genny) are AFCI protected. The easiest solution would be to replace my sub with a much larger panel... but the problem is the wall cavity where my sub is located isn't a full 16" OC and I've yet to find any larger main panels with a shorter width that would fit my space. The think the next easiest way would be to add an additional sub panel to give me more breaker space but I'd like to maximize my space across both sub panels.

So my question: Since I will be protecting my feed from the main panel with an interlocked breaker setup, is it possible (doesn't violate code, any required labeling used, doesn't exceed amp limits of either sub panel, un-bonded neutral and ground, etc) to connect the two sub panels via their lugs to effectively create a single large sub panel and have them both fed by the interlocked breaker setup in the first sub panel?

I've searched all over this forum, others, and the NEC code book but haven't come across anything the prohibits this. Thought I'd try posting the question here.

Thanks in advance!

 

[ptavares]

Moderator: since I don't have a way of communicating after a thread is closed... I am an electrical engineer that assists in selling electrical equipment. Does that not qualify me to post on this board?

 

[Dennis Alwon]

Moderator: since I don't have a way of communicating after a thread is closed... I am an electrical engineer that assists in selling electrical equipment. Does that not qualify me to post on this board?

Unfortunately we cannot allow diy threads unless you are an electrician. There has been much debate about this as we have many moderators who are ee's and they cannot ask diy questions.

This has been the rule of the forum since before I came onboard. Sorry