I wired two circuits for dryer and water heater. I installed an electrical box on the wall right above the electrical panel, fished NM 10/3 and NM 10/2 through the wall, and run 5 THHN #10 wires in a 1/2'' EMT.
Because the wall is between the house and the garage I wanted to avoid making a big opening, installing the box flush to the wall and having a box extension for the EMT conduit. So I decided to install the box on top of the wall, run the NM cables in two holes and fire block just the two holes.
But I forgot to do a box fill calculation so I had to install a box extension after all... Having 10 conducting wires of gauge 10, NM connectors (this which I think counts as internal and this which should count as external), and 2 grounding wires requires 30 cu in. In retrospect I should had installed a deep square box of 30.5 cu in instead of the current one that is 21 cu in. To satisfy the minimum box fill volume I added an extension box and now I'm at 41 cu in so I'm good. But it looks weird and ugly. Am I violating any code with this setup? I'm in California. Are there any other smaller box extensions I could use that would give me the 9 cu in I'm missing?
If you notice any code violations from the pictures below please let me know.
Box above the electrical panel with two NM cables fished behind the wall and EMT conduit going to the next box:
Box above existing dryer outlet with NM cable fished behind the wall going to the outlet below and with liquidtight whip attached on the left for the water heater:
Dryer outlet that replaced a NEMA 10-30R:
Changed the wiring on the dryer to 4 wires:
Electrical sub panel: I capped the 2 hots of the previous dryer wiring with a wire nut, installed two Raco the insider NM connectors for the two orange NM cables, replaced the old handle-tied 30A breakers for the dryer with a new GFCI 30A breaker, and replaced two 15A breakers with a 4-pole quad circuit breaker to get 30A for the water heater.
Electrical sub panel photos before I did any work. I had to move some breakers around to move the tandem breakers at the bottom and also make space for the water heater breaker.
For completeness, main panel from top to bottom: solar, EVSE, air handler, heat pump, service disconnect, surge protector, power meter for EVSE load management, subpanel, driveway lights and plug.