392.8 Cable Installation.
(A) Cable Splices. Cable splices made and insulated by approved methods shall be permitted to be located within a cable tray, provided they are accessible and do not project above the side rails.
(B) Fastened Securely. In other than horizontal runs, the cables shall be fastened securely to transverse members of the cable trays.
(D) Connected in Parallel. Where single conductor cables comprising each phase or neutral of a circuit are connected in parallel as permitted in 310.4, the conductors shall be installed in groups consisting of not more than one conductor per phase or neutral to prevent current unbalance in the paralleled conductors due to inductive reactance.
Single conductors shall be securely bound in circuit groups to prevent excessive movement due to fault-current magnetic forces unless single conductors are cabled together, such as triplexed assemblies.
The binding or otherwise grouping of 3-phase circuits is good engineering practice. If properly done, it results in the phase reactances of the conductors being balanced, which reduces the voltage unbalance between the phases of the 3-phase circuit.
