When installing insulated conductors of 4 AWG or larger, the minimum dimensions of pull or junction boxes installed in a raceway or cable run must comply with 314.28(A)(1) through (A)(3). The rules apply to “insulated” conductors for a reason. When installing large, insulated conductors, care must be taken to ensure that the conductor insulation is not compromised during the wire pull because the box is too small.

Section 314.28(A)(2) provides the minimum required dimension for an enclosure containing an angle pull, U pull or even splices. For angle pulls, U pulls or splices, the distance between each raceway entry inside the box or conduit body and the opposite wall of the box or conduit body shall not be less than six times the trade size of the largest raceway in a row but the exception below makes a special allowance for conductors that enter the back of an enclosure opposite a removable cover (see image).

“Exception: Where a raceway or cable entry is in the wall of a box or conduit body opposite a removable cover, the distance from that wall to the cover shall be permitted to comply with the distance required for one wire per terminal in Table 312.6(A)” as seen in part below:

NEC Table 312.6(A) provides minimum wire-bending space dimensions at terminals and minimum width of wiring gutters. Table 312.6(A) applies where conductors do NOT enter or leave the enclosure through the wall opposite their terminals which describes the typical installation where conductors enter the back of the enclosure opposite the removable cover.

See the actual NEC^® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to NFPA 70.