312.7 Space in Enclosures.
Cabinets and cutout boxes shall have approved space to accommodate all conductors installed in them without crowding.
312.8 Switch and Overcurrent Device Enclosures with Splices, Taps, and Feed-Through Conductors.
The wiring space of enclosures for switches or overcurrent devices shall be permitted for conductors feeding through, spliced, or tapping off to other enclosures, switches, or overcurrent devices where all of the following conditions are met:
1. The total of all conductors installed at any cross section of the wiring space does not exceed 40 percent of the cross-sectional area of that space.
2. The total area of all conductors, splices, and taps installed at any cross section of the wiring space does not exceed 75 percent of the cross-sectional area of that space.
3. A warning label complying with 110.21(B) is applied to the enclosure that identifies the closest disconnecting means for any feed-through conductors.