4

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).

  • Real question. I won't self-answer. This is where I'm stuck. – Harper - Reinstate Monica Apr 12 at 4:34
  • I'd say that you would be complying with those regulations. I don't know if putting two cables in one clamp is permitted. – Jasen Apr 12 at 6:04
  • some Metal clamps do allow 2 cables , but I believe the 2 cables would have to be in 1 conduit or wireway. I believe the insiders I use that are plastic allow for 2 but only pull 1 through. – Ed Beal Apr 12 at 6:38
2

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."

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  • Since non-metallic cables are implied by 300.3(B)(3), 300.20(B) applies, but only to multiple entries into a metallic box. Same entry or nonmetallic box should comply. – Harper - Reinstate Monica Apr 12 at 19:47
-1

I do not think so and the reason is maybe a little simplistic but 2 Romex in parallel would have 2 whites , I have run 12-2-2 and the inspector let it slide because it was in 1 cable and well identified with red paint pen and said 12-4 or smurf tube in the future. Remember the white in a switch leg we run the hot on the white and reidentify as required by code 200.7.c.1 separate cable with 2 whites would put you in the jeopardy as separate. Inside a raceway or conduit it can be done but that would be silly who would do that. Most of us use smurf tube for 3 & 4 ways now. Because 12-4 cost $$

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  • Wait, the inspector hassled you for 12-2-2 (12/4 with two whites, one with a red stripe) and remarking the white-red???? That is bizarre. – Harper - Reinstate Monica Apr 24 at 3:19
  • After the change requiring a neutral the inspector said we should not be identifying a white as a hot being in separate cable would be worse than the 12-2-2 I did not fight it as many times I do run smurf , my understanding was the. Conductors have to be in the same cable or raceway would be the other reason. – Ed Beal Apr 24 at 14:07

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