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I'm preparing to add 4 new 12/2 cables for new circuits.

All existing branch cables in my panelboard enter through snap-in grommets grouped near the upper left and upper right. I thought it would be possible to use the top center knockout for new runs, but then I looked in the attic.

Above the wall, all of the smaller circuits are jammed into two 1.5" holes in the header, right next to a third hole for the oven, dryer, and air conditioning. They are not spaced out the same way as in the panelboard.

Above the wall

Is there any realistic chance of fishing 4 more cables in that same stud bay? If I had to guess, I'd say the smaller circuits are up against the left stud, leaving about 6 inches of empty space to the right of the oven circuit.

My alternative idea is to leave all that alone, cut open the wall below the panelboard, drill a couple 3/4" holes through the stud, and do my fishing in the next bay over. The bays left and below the panelboard should be empty other than a ground wire or two.

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So if I understand correctly, you plan on coming down an adjacent bay, go thru the stud and come up in the bottom of the panel. I think that's a great idea. I'd go with 1" holes rather than 3/4". So often I've done 3/4" and regretted it.

There is another issue though. I really doubt (maybe others could chime in) that the bundle of cables so tightly spaced that it was never code legal to start with. So adding to it would be a big mistake. That's why I really like your plan to avoid it entirely. Current code only allows 3 cables (4 if you get an understanding inspector) per hole regardless of size. Nothing to be done about it now. The reason for the code is to avoid heat buildup. I think that code requirement is over-kill, but it has obviously been working for you for some time.

So yeah, keep away from that bundle, run the new cables in the adjacent stud bay and come in underneath on the main panel. GREAT IDEA, GOOD PLAN!

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    Even if it were to code to fish another cable through that mess (which I don't think it is), it would be extremely difficult to do so. I would highly recommend pulling a piece of heavy string/light rope with the new cable(s) in order to facilitate pulling future NM-B in the future. While you've got the wall open, make it easier for future you!
    – FreeMan
    Commented Aug 31, 2022 at 14:16
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    @FreeMan good idea. But how would that work with NM going thru holes? I'd think it'd get hung up. Maybe a chunk of conduit with a 90 at the bottom would be good, or a smurf tube or two. ....thoughts?
    – George Anderson
    Commented Aug 31, 2022 at 14:32
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    Of course, having conduit and pulling THHN (or similar) would be even easier, but that means having a JB at the top of the conduit run where you then transition to NM for the rest of the run through the attic to wherever.
    – FreeMan
    Commented Aug 31, 2022 at 15:22
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    @GeorgeAnderson Just to clarify, MA = male adapter, JB = junction box, and your comment is specifically about NM cable inside conduit. If there's THHN in the conduit, then the box would be needed in the attic, which is probably the easiest part of the whole task.
    – Robert Chapin
    Commented Aug 31, 2022 at 15:44
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    @RobertChapin Yes, if transitioning from NM to THHN/THWN a box would be required and be "permanently accessible". I don't like anymore connections than needed, so that's why I mentioned NM in conduit. BTW, I've had to do exactly what you said on a rental property. I ran THHN/THWN in a conduit along the side of the house, under a deck and transitioned to NM via a rain tight, exterior box into the attic. I didn't want to deal with conduit in the attic when NM is perfectly OK.
    – George Anderson
    Commented Aug 31, 2022 at 16:13

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