I have always presumed that currents must be equal in the same cable or conduit, and one shouldn't use multiple cables for 4-5 conductors because of eddy current heating, induced vibration causing metal fatigue, etc.
However, then I closely examined the following Code:
300.3(B) Conductors of the Same Circuit. All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors and bonding conductors shall be contained within the same raceway, auxiliary gutter, cable tray, cablebus assembly, trench, cable, or cord, unless otherwise permitted in accordance with 300.3(B)(1) through (B)(4).
300.3(B)(3) Nonferrous Wiring Methods. Conductors in wiring methods with a nonmetallic or other nonmagnetic sheath, where run in different raceways, auxiliary gutters, cable trays, trenches, cables, or cords, shall comply with the provisions of 300.20(B).
300.20(B) Individual Conductors. Where a single conductor carrying alternating current passes through metal with magnetic properties, the inductive effect shall be minimized by (1) cutting slots in the metal between the individual holes through which the individual conductors pass or (2) passing all the conductors in the circuit through an insulating wall sufficiently large for all of the conductors of the circuit.
Provided that you either a) use a plastic box, b) enter both cables on the same cable clamp, or c) slot the box as discussed…
Is that authorizing the use of two /2 cables in lieu of a /4, e.g. in a 3-way switch loop where neutral is needed?
Edit: I've italicized the relevant snippets, and here they are alone:
300.3(B) Conductors of the Same Circuit. All conductors of the same circuit shall be contained within the same cable, unless otherwise permitted in accordance with 300.3(B)(1) through (B)(4).
300.3(B)(3) Nonferrous Wiring Methods. Conductors in wiring methods with a nonmetallic sheath, where run in different cables, shall comply with the provisions of 300.20(B).
Best Answer
No.
The language in 300.20(B) refers specifically to a single conductor, not a single cable.
300.3(B) mentions "in a single cable" unless otherwise allowed, and I don't read 300.3(B)(3) or 300.20(B) as allowing otherwise.
I would guess the exceptions are intended for where you need to run a pair of conduits to physically accommodate large feeder wires; Which are "individual conductors."