New provisions for power distribution blocks in pull and junction boxes have been added.

314.28 Boxes and Conduit Bodies for Conductors 4 AWG and Larger.

(E) Power Distribution Block. Power distribution blocks installed in junction boxes over 100 cu in. must comply with the following (click here to see Fig. 15):

(1) Installation. Be listed as a power distribution block.

(2) Size. Be installed in a box not smaller than required by the installation instructions of the power distribution block.

(3) Wire-Bending Space. The junction box is sized so that the wire-bending space requirements of 312.6 can be met.

(4) Live Parts. Exposed live parts on the power distribution block aren’t present when the junction box cover is removed.

(5) Through Conductors. Where the junction box has conductors that don’t terminate on the power distribution block(s), the through conductors must be arranged so the power distribution block terminals are unobstructed following installation.

Analysis: Power distribution blocks have a history of being used in large pull and junction boxes despite the fact that the Code has been silent on these installations. The only requirements for power distribution blocks were found in Art. 376, which applies only to metal wireways. This left uncertainty regarding the installation requirements for these blocks in boxes. The NEC now addresses this practice and provides clear, concise rules.

Only boxes exceeding 100 cu. in. can contain these blocks, and they must be listed. The values in Table 312.6 can be used for bending space at the terminals, and live parts must be covered just as required for wireways.