What Are the Wire Bending Space Requirements for My Conductor Size?
Section 312.6 governs wire bending space in cabinets, cutout boxes, and meter socket enclosures, and it has two tables that do different jobs. Table 312.6(A) sets the minimum width of wiring gutters, meaning the space where conductors run past a terminal. Table 312.6(B) sets the minimum bending space at terminals, and it is the one that actually controls whether a large conductor can be landed without violating its bend radius.
Which table applies
Table 312.6(A) applies to the wire bending space at the top, bottom, and sides of the enclosure where conductors do not enter or leave through the wall opposite the terminal. Think of the vertical gutter alongside a panelboard bus where feeders pass through on their way to a lug.
Table 312.6(B) applies where the conductor enters or leaves the enclosure through the wall opposite its terminal. This is the deep case, because the conductor has to make a full 90 degree bend inside the enclosure to reach the lug. Section 312.6(B)(1) covers conductors not entering or leaving opposite the terminal, and 312.6(B)(2) covers those that do.
Numbers from Table 312.6(B), one conductor per terminal: an 8 AWG needs 1.5 inches, a 4 AWG needs 3 inches, a 2 AWG needs 3.5 inches, a 1/0 needs 5.5 inches, and a 4/0 needs 7 inches. A 250 kcmil needs 8.5 inches. Add conductors per terminal and the required space grows, since the table has separate columns for two, three, four, and five conductors per terminal.
Why this fails on real jobs
A 200 ampere residential panel with 4/0 aluminum service conductors coming in through the back needs 7 inches of bending space in front of the main lugs. Standard load center enclosures are only about 3.75 inches deep. This is why service conductors come in through the top or bottom knockout of a load center rather than through the back wall, since that puts you on 312.6(B)(1) or on Table 312.6(A) instead of the deep 312.6(B)(2) case.
The same rule quietly limits how many large conductors you can pass through a wireway or a gutter. Section 376.22 caps a wireway at 20 percent fill for conductors, and 376.23(A) requires that wire bending space at any point where conductors enter or leave be at least the distance in Table 312.6(A). Where a conductor is deflected more than 30 degrees, 376.23(B) applies the pull box sizing rules of 314.28.
The related rules that travel with it
Section 314.28 governs pull and junction boxes for conductors 4 AWG and larger. For straight pulls, the box length must be at least eight times the trade diameter of the largest raceway. For angle or U pulls, the distance from the raceway entry to the opposite wall must be at least six times the trade diameter of the largest raceway, plus the sum of the diameters of the other raceways in the same wall and row.
Section 110.26 sets the working space in front of the enclosure, which is a different measurement made outside the box: 30 inches wide, 36 inches deep at 120/240 volts, and 6 feet 6 inches of headroom.
And 110.12 ties it together. A conductor forced into a space too small for its bend radius shows kinked insulation and a compressed jacket, which is both a workmanship violation and a real reduction in the conductor's insulation integrity at the exact point where it carries the most current.